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REFERENCE

;39

Properties and interactions of

Oral Structures and Restorative

Materials

J. iesk, J. Antonucci, G. Brauer, J. McKinney, R. Penn, J. Stansbury,

W. de Rijk. S. Venz, H. lizuka, S. Lee and K. Asaoka

U.S. DEPARTMENT OF COMMERCE

National 3ureau cf Standards

institute for Materials Science and Engineering

Polymers Division

Dentai and Medical Materials

Gaithersburg, MD 20899

Annual Report for Period

October 1, 1985 to September 30, 1986

issuea March 1987

Interagency Agreement

Y01-DE30001

-QC

100

.1156

# 87-3539

1987

j for

al institute of Dentai Research

»da, MD 20205

NBSIR 87-3539

MBS

RESEARCH

INFORMATION CENTER

PROPERTIES AND INTERACTIONS OF

ORAL STRUCTURES AND RESTORATIVE

MATERIALS

&aoo

J. Tesk, J. Antonucci, G. Brauer, J. McKinney, R. Penn, J. Stansbury,

W. de Rijk, S. Venz, H. lizuka, S. Lee and K. Asaoka

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Institute for Materials Science and Engineering

Polymers Division

Dental and Medical Materials

Gaithersburg, MD 20899

Annual Report for Period

October 1, 1985 to September 30, 1986

Issued March 1987

Interagency Agreement

Y01-DE30001

Prepared for National Institute of Dental Research

Bethesda, MD 20205

U.S. DEPARTMENT OF COMMERCE, Malcolm Saldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

CONTENTS

ABSTRACT . . . i

FY 86 SIGNIFICANT ACCOMPLISHMENTS ii

STAFF BIOGRAPHICAL SKETCH iii

INTRODUCTION iv

PART I - COMPOSITES, CEMENTS, AND ADHESION (Brauer, Stansbury,

Antonucci, Venz , Iizuka, and Lee)

Section A through D - Brauer

A. High-strength Eugenol-free Adhesive Cements

and Restoratives .1

References 4

B. Changes in Esthetic Properties of Dental

Resins on Aging 6

C. Development of Radiopaque Copolymeric Denture

Resins 7

References 10

D. Study of Adhesion and Adhesion Promoting Agents

to Dentin 11

References 21

Publications 22

Manuscripts Under Review or Accepted for Publication .... 22

Invited Talks 22

Contributed Talks 22

Section E - Stansbury

E. Monomers Which Polymerize with Expansion 23

References 27

Publications 27

Manuscripts Under Review or Accepted for Publication .... 27
Contributed Talks 27

Section F - Antonucci

F. Improvement of Dental Composites, Sealant Cement

and Adhesive Materials. 28

I. Improvement of Dental Resin Systems for

Composites and Sealants 29

II. Improvement of Dental Cements. ......... 34

III. Improvement of Interfacial Bonding Systems and

Fillers for Composites and Cements . 37

IV. Bonding of Low Surface Energy Resin Systems

to Tooth Structure 41

References 44

Patents 47

Publications 48

Manuscripts Accepted for Publication 48

Manuscripts Approved by VERB 48

Manuscripts Under Review by VERB 48

Invited Talks 48

Contributed Talks 49

PART II - WEAR RESISTANCE AND DURABILITY ASSESSMENT OF

OF DENTAL COMPOSITE RESTORATIVE MATERIALS

(McKinney, Antonucci, Penn, de Rijk and Venz)

A. Wear and Durability Assessments of Composite

Restoratives 57

B. Glass-Transition Temperature (Tg) of Matrix Polymers. .61

C. Wear Instrumentation 62

D. Clinical Examinations Employing Removable Partial

Dentures 63

References 65

Publications 66

Manuscripts Under Review 66
Manuscripts Approved by WERE . . . . 66

Manuscripts Submitted to WERE- . . . . . . . . . . . . . . . 66

Contributed Talks. ..................... 66

PART III DENTAL ALLOYS , CERAMICS, AND METROLOGY

(Tesk, Penn, de Rijk and Asaoka)

A. Porcelain-alloy Compatibility (Thermomechanical Stress) .................. .68

B. Porcelain-alloy Compatibility. ............ .69

C. Castability (Filling of a Mold with Cast

Dental Alloy) ..................... .72

D. Castability (Accuracy of Fit of Dental Castings) . . . .75

E. Metrolggy and Clinical Performance. .......... 76

References. ......................... 81

Publications. ........................ 81

Manuscripts Under Review or Accepted for Publication. .... 82

Invited Talks .............. .... 82

Contributed Talks ...................... 84

ABSTRACT

The research program described herein is designed to achieve a number of

objectives leading to improved dental restorative materials, techniques and

applications of dental materials science for improved dental health care in

general. Some of the research in dental composites is directed toward

developing generic polymer science potentially useful for composite

applications, e.g., durable resin matrices and stronger more durable coupling

between fillers and resins. Improved reinforcement is sought by defining the

type, and percentages of fillers which will result in improved performance of

composites. Methods for reducing polymerization shrinkage and attendant stress

and marginal leakage are also explored. Cements are investigated and basic

formulations developed for lower solubility, higher biocompatibility, higher

strength, greater toughness and adhesion to various substrates including enamel

and dentin. Analysis techniques include IR spectroscopy, chromatography, x-ray

analysis, mechanical testing, and dilatometry. Another major effort is

directed at elucidating the fundamentals involved in wear and degradation of

dental composites and restoratives. Wear and hardness measurement techniques

are pursued as well as by identification of the origins and sources of flaws

leading to failure. Weibull statistical analysis is expected to provide useful

information for this task. In this regard an objective is to investigate

improved correlations between clinical results of wear and failure of

composites with laboratory test data via time-to-f allure analysis. Metrology

and analysis constitutes the underlying theme of investigations into porcelainmetal systems, casting of dental alloys and the expansion of dental casting

investments

.

"The activity covered by this agreement consists of work which requires

the definition of measurement methods, materials property data, and

standards of basic scientific and engineering units and the application

of primary standards to insure equity and comparability in U.S. commerce,

international trade, and technical activities. As such it complies with

OMB Circular A-76, revised under paragraph 5f (Activities classified as Government responsibilities or are intimately related to the public

interest) .

i
FY 86 SIGNIFICANT ACCOMPLISHMENTS

o Cooperative studies with other institutions on the

biocompatibility of Zinc Oxide Hexyl Vanillate Cements indicate

that their biological performance is acceptable.

o An NBS - American Dental Association collobrative effort on evaluation of Syringate -Vanillate -EBA-ZNO cements indicates that

this material is suitable for clinical evaluation.

o A radiopaque denture base formulation employing pentabromophenyl

methacrylate as a polymerizable radiopaque agent was shown to be

color stable.

o Adhesive formulations with the potential for use in dentin bonding

and repair of manillofacial fractures were prepared and showed

promise for continued research after early testing.

o Effects of film thickness and power/liquid ratios on retention of

dental cements showed that composition of the brand was more influential than the type of cement.

o The use of expanding monomers in dental adhesives was found to

result in increased bond strength. This is attributed to lower

residual stress due to less shrinkage during curing.

o Silyl ether derivitives of Bis-GMA were found to import a variety

of desirable properties to experimental dental composites.

o Amine salts and complexes were found to import improved color

stability to resin based dental system.

o Resin-modified dimer-acid cements were shown capable of producing

high tensile strength materials which may have utility as intermediate restoratives, bases, and liners.

o A modified glass - ionomer cement formulation was developed and shown

to be stronger in tension with less susceptibility to hydration

during setting.

o Dual silanization of composite fillers showed promise of yielding

more durable composites. The use of a newly synthesized

multifunctional silane coupling agent improved the hydrolytic

stability of an experimental dental composite.

o Res in- toughened glass ionomer cement-composites were found to

exhibit only slightly increased wear and without the brittle

failures normally associated with conventional glass - ionomer

cements

.
o The effects of various elements on the castahilitv of Ni-Cr alloys

was determined as a function of alloy and mold temperatures. A synergistic effect between Si and Be was found.

o Continued experimentation on the internal setting expansion of

dental phosphate-bonded investment showed internal setting strain

of only .15%, between directions perpendicular to each other.

o Weibull statistical analysis has shown that some dental composite

restoratives may be more prone to marginal failure than others.

o Confidence limits for Weibull statistical analyses were obtained by

numerical methods.
'

.
DENTAL AND MEDICAL MATERIALS GROUP

J.A. Tesk, Group Leader

Research Associates

NBS Personnel Paffenbarger Res. Ctr. NIDR Industry

J.M. Antonucci R.L. Bowen, Director E.D. Eanes S. Venz,

G.M. Brauer W.E. Brown, Dir. Em. B.O. Fowler Dentsply

N.C. Chapwick R e L c Blosser A.W. Hailer R. Muller,

W.G. deRijk C.M. Carey Astron Co: J.E. McKinney M.W. Chalkley

R.W. Penn L.C. Chow

J.W. Stansbury N. Eidelman

F. Eichmiller

A. A. Giuseppetti

T.M. Gregory

A.D. Johnston ° D. Kirkpatrick

A. Ly

M. Mathew

D.N. Misra

E.F. Prestemon

N.V. Rupp

C.T. Schreiber

B. Sieck

S. Takagi

B.B. Tomazic

M.S. Tung

G.L. Vogel

R.M. Waterstrat

Guest Scientists Consultants

K. Asaoka, Tokushima Univ R. Natarajan, U. of Illinois

E. Asmussen, Copenhagen, R • D.C. P. Sung, U.S. Food 4 Drug Adm

T. Chen, U.S. Food & Drug Adm. G. Widera, U. of Illinois

E. Cobb, Georgetown Univ.

R'. Engler, U.S. Navy

W. Grant, A.D.A.

B. Heywood, NIDR

H. Iizuka, Nihon Univ.

C. Lee, W. China U. of Medical Sci.

M. Markovic, Hebrew Univ.

J. Meyer, NIDR

A. Sugawara, Nihon Univ.

•V. Thompson, Univ. of Maryland

M. Waterman, U.S. Navy
PROPERTIES AND INTERACTIONS OF ORAL

STRUCTURES AND RESTORATIVE MATERIALS

INTRODUCTION

The following pages contain reports on work involved with the development

of basic generic science and engineering which is expected to be useful in the

development or control of dental materials used for restorative or treatment

purposes. Some of the developments involve investigations into new dental

resin formulations (Part I) which might improve the performance of dental

composites. Cements and adhesion to filler particles or tooth structure are also addressed in this part.

Part II deals with examination of the basic parameters affecting the wear

and durability of materials with particular emphasis on dental composites. The

resultant information is used to help guide developments in Part I.

Parr III is concerned with dental casting alloys, and the strength of,

veneered dental systems, in particular, porcelain fused-to-metal . Factors

affecting the castability of alloys and how to measure and define aspects of

castability are addressed. Mathematical methods are employed to reveal effects

of individual elements as well as other parameters. The strength of veneered

systems is the characteristic receiving the most attention for the porcelainf used-to-raetal studies. Special emphasis is being placed on measurement

rechnigues and flaw analysis.
I COMPOSITES, CEMENTS AND ADHESION

A. High-strength Eugenol-free Adhesive Cements and Restorations

Overview

Cements are used in over 50 percent of all dental restorations. Zinc

oxide-eugenol type cements, because of the excellent biocompatibility of

the hardened material, are employed for such diverse applications as cementing media for crowns and bridges, sedative and insulating bases,

temporary restorations, pulp capping agents, root canal sealers, soft

tissue packs and as impression pastes.

Cements in current use are far from ideal. Their relatively low

mechanical properties, high solubility and lack of resistance to wear and

disintegration deters their more extensive use, especially for

cementation for permanent protheses or for their use as intermediate

restoratives

.

Non-eugenol containing cements based on vanillate esters, o- ethoxybenzoeic acid (EBA) and zinc oxide, have been developed in this

laboratory [1-7] . These cements have the following advantages compared

to the presently used Zinc Oxide Eugenol (ZOE) or EBA cements: (1)

excellent strength, (2) much lower solubility than zinc oxide-eugenol

cements, (3) do not inhibit free radical polymerization and can be used

in conjunction with composite filling materials to which they adhere, (4) are compatible with acrylic monomers and can be formulated in conjunction

with them, (5) adhere strongly, even on prolonged water exposure, to non- precious metals, porcelain and composites. The cements exceed greatly

requirements of ANSI/ADA Specification No. 30 for Types II, III, and IV

restoratives

.

Objective

The initial objective of this study was to synthesize and evaluate these

cements for various dental applications. To achieve this objective the

following tasks were undertaken: (1) synthesis and evaluation of

aivanillates and polymerizable vanillates such as methacryloylethyl

vanillate and addition of these compounds to hexyl vanillateethoxybenzoic acid (HV-SBA) cements to improve mechanical properties; (2)

quantitative measurements of the adhesive properties of HV-EBA cements;

(3) formulation of intermediate restorative materials (IRM) incorporating

monomers and reinforcing fillers with cement ingredients and

determination of their mechanical properties; (4) synthesis of cements

containing the potentially caries-reducing syrmgic esters and evaluation

of properties of the resulting cements; (5) modification of the cements

by addition of small concentrations of additives such as acids, metals or fluorides to improve their properties and (6) to furnish assistance and

guidance to conduct investigations of the biocompatibility and toxicity

of the cement and its ingredients and to collaborate in studies of the

pulp irritation and in clinical studies at various dental research

centers

.

1
Accomplishments

Objectives 1-5 have been completed. Results of these studies have been

summarized in References 1-16. They have lead to a number of cements and

intermediate restoratives of potentially great usefulness for clinical

dentistry.

Present objectives will be directed to (1) further improvements of the

vanillate or syrxngate cements by addition of modifying agents, (2)

increase the scope of the usefulness of these materials for clinical

dentistry, (3) completion of studies of the biocompatibility of syringate

cements and cement-composites containing acrylic monomers.

PROGRESS REPORT

Phase I. Further improvement of properties of vanillate and related

cements

Because of the emphasis placed on other portions of research

conducted under this interagency agreement, no studies were carried

out on these phases (la, lb, lc) during the year.

Phase II. New applications of these materials (Id and le)

No studies were conducted on these phases (Id and le) during the

year due to emphasis on other portions of the research.

Phase III. Study of the Biocompatibility and Clinical Usefulness of

Vanillate and Syringate Base Restoratives

(1) Biocompatibility

(a) Biological Performance of Zinc Hexyl Vanillate Cements.

Studies conducted by J.C. Keller and co-workers of the Dental

School, University of South Carolina of cements furnished by

this laboratory were presented at the annual AADR meeting.

They showed that the cellular and connective tissue reactions

of the vanillate cement approximated those of zinc phosphate

and ZOE cements. (Overall cell counts were lowest for the

vanillate cement; however, the differences were not

significant.) The investigators concluded that the vanillate

cement had acceptable biological performance as compared to

the clinically acceptable phosphate or ZOE cements.

(b) Biocompatibility of Syringate-Vanillate-EBA-ZnO cements.

The biological safety evaluation of syringic acid ester

cements has been conducted by Dr. Siew and co-workers at the

American Dental Health Foundation. Oral LDso for 2-

ethylhexyi syringate (EHS) is approximately 5.3 g/kg, that is even lower than that of hexyl vanillate. Red blood cell

hemolysis, cloning efficiencies and Ames mutagenicity tests

2
with four bacterial strains of EHS or the cement extract were negative. Although these toxicity and mutagenicity tests are

not exhaustive, the data indicate in both procaryotic and

eucaryotic (mammalian) cell systems along with whole animal

studies that this cement is neither toxic nor mutagenic.

Thus, clinical testing of this cement is justified.

(c) Biological evaluation of vanillate-intermediate

restoratives. Three formulations synthesized in this

laboratory containing dicyclopentenyloxyethyl methacrylate or cyclohexyl methacrylate which have much better mechanical

properties than commercial intermediate restoratives and bond

well to composites, non-precious metal or porcelain are being

evaluated for biological characteristics at the American

Dental Association Health Foundation, the University of Texas

at San Antonio and University of Tennessee Dental School.

(2) Assistance in Clinical Evaluation. A very limited clinical

study of the cement has been initiated at the University of

Louisiana School of Dentistry. Mo undesirable behavior has

been reported after the four-month clinical observation

period.

3
References

[1] Brauer, G.M., Argentar, H. and Stansbury, J.W. Cementitious Dental

Compositions Which Do Not Inhibit Polymerization, U.S. Patent 4,362,510,

December 7, 1982.

[2] Brauer, G.M. and Stansbury, J.W. Development of High-Strength, Acrylic

Resin Compatible Adhesive Cements, J. Dent. Res. 62 366-370 (1983).

[3] Stansbury, J.W. and Brauer, G.M. Divanillates and Polymerizable

Vanillates as Ingredients of Dental Cements, J. Biomed. Met. Res. 19 715-

725 (1985).

[4] Brauer, G.M. and Stansbury, J.W. Intermediate Restoratives from n-Hexyl

Vanillate-EBA-ZnO-Glass Composites. J. Dent. Res. 63 1315-1320 (1984).

[5] Brauer, G.M. and Stansbury, J.W. Cements Containing Syringic Acid

Esters-o-Ethoxybenzoic Acid and Zinc Oxide. J. Dent. Res. 63_ 137-140

(1984).

[6] Brauer, G.M. and Stansbury, J.W. Biocompatible Cementitious

Compositions. U.S. Patent 4,486,179 Dec. 4, 1984.

[7] Brauer, G.M., Stansbury, J.W. and Flowers, D. Modification of Cements

Containing Vanillate or Syringate Esters. Dent. Mat. 2 21-27 (1986).

[8] Stansbury, J.W. and Brauer, G.M. Properties of Vanillate and Syringate

Cements Containing Various Fluorides. IADR Prog, and Abst. 64, No. 314

(1985) .

[9] Slew, C., Gruninger, S.E., Hsu, R., Brauer, G.M. and Tesk, J.A.

Biological Safety Evaluation of a Newly Developed High Strength Acrylic

Resin Compatible Adhesive Cement. IADR Prog, and Abst. 64 No. 1473

(1985) .

[10] Siew, C., Gruninger, S.E., Brauer, G.M. and Tesk, J.A. Biological Safety

Evaluation of Syringic Acid Ester Cements, IADR Prog, and Abst. 65 No.

1337 (1986)

.

[11] Miller, E.G., Washington, V.H., Zimmerman, E.R. and Bowles, W.H. IADR

Prog. Abst. y No. 1273 (1984).

[12] Kafrawy, A.H. and Phillips, R.W. Pulp Reactions to Hexyl VanillateEthoxybenzoic Acid Cement. IADR Prog, and Abst. y No. 2 (1984).

[13] Rubinoff, C.H. and Greener, E.H. Physical Properties of an experimental

Dressing Material. Dent. Mat. 1 3-6 (1986).

[14] Glickman, G.N., Goldberg, H., Loevy, H., Gross, R.L. and Greener, E.H.

Sealing and Biocompatibility of an Experimental Endodontic Sealer. IADR

Prog, and Abst. 6A No. 77 (1985).

4
C15] Stansbury, J.W. and Brauer, G.M. Bonding of Vanillate and Syringate

Cements to Various Substrates. IADR Prog, and Abst. 64 No. 393 (1984).

[16] Keller, J.C. Hammond B. and Kowalyk, K. Biological Performance of Zinc

Hexyl Vanillate (ZHV) Cements. IADR Prog, and Abst. 65^ No. 1343 (1986) .

C
B. Changes in Bathetic Properties of Dental Resina on Aging

Overview

Although the color stability of the presently employed dental resins is

quite satisfactory, some discoloration of these materials can often be

observed clinically. Under oral conditions, these restorations are exposed to the combined effects of light, moisture, stains and mechanical

wear resulting in visibly detectable, and aesthetically undesirable color

changes. Many of these changes are the results of photochemical

reactions of ingredients of the composite caused by exposure of the

restoration to various energy sources. Since clinical studies to

determine color stability of restoratives are time-consuming, accelerated

aging tests have been suggested to correlate laboratory findings and

clinical performance. Most of these tests are based on short-term (24

hour) exposure of the materials to light sources or heat, often in an aqueous environment.

Objective

The objective of this study was to (1) investigate the color changes of a wide variety of dental resins resulting from the exposure to different

radiation sources or to thermal exposure, under diverse environmental

conditions for various periods of time, and (2) to try to correlate the

experimental in vitro results with the composition of the materials as well as with their clinical performance. Results of this investigation

should establish which ingredients of composites are responsible for

color instability. Such data should assist in the development of more color stable resins.

Accomplishments

The results of the color stability of composites on exposure to

irradiation by (1) a 150 Klux Xenon lamp, (2) a standard RS light source

and (3) elevated temperature at 60 °C, in air or water and under

different experimental conditions for various time periods were reported

in last year’s report.

PROGRESS REPORT

Phase I. Characterize minor components of the composites. Correlate

aging behavior with presence of specific ingredients

Thermal exposure studies of the chemical or light cured, hybrid or microfillea, composites were extended for up to one year.

Composites kept in the dark at 37 °C for one year showed no color

changes. Materials stored in an oven at 60 °C did not discolor

appreciably for at least six months except for the chemically cured

Adaptic and Silar. Mere rapid and severe discoloration occurred in

water with most specimens undergoing changes in the color ratings

after one month. Color changes were observed by nearly ail

observers on viewing of all composites stored in water for six

6
months. All materials gave perceptible or very perceptible color

changes on 12 month storage in this medium.

The pastes of a number of brands were dissolved and subjected to

high pressure liquid chromatography. Many ingredients present in

the pastes could be identified from the chromatograms. A complete

identification of all major and minor components in composite

pastes will only be possible with a preparative chromatograph.

These studies were discontinued until such time when equipment

becomes available to separate, for further identification, larger

quantities of ingredients.

A manuscript summarizing these studies was prepared and is now

under editorial review. It includes comparison of our laboratory

data with clinical studies of color changes of two of the

chemically cured composites. The data indicate that these two

restoratives, which pass the ANSI/ADA or ISO specification tests, cause discoloration in clinical use after two to three years.

Phase II. If clinical experience with modern composites is favorable,

then formulate new composites with improved color stability and aging

characteristics

.

No work on this phase is anticipated in the near future.

C. Development of Radiopaque Copolymeric Denture Resins

Overview

The ever increasing use of plastics, in dentistry makes it desirable and

often even mandatory that such materials have adequate radiopacity to

detect their presence in various environments [1] . Radiopacity is an important requirement for medical and dental implants or devices that may

be ingested accidentally. The commonly available high molecular weight

plastics are composed of elements of low atomic number. The low crosssectional electron density of the polymer chain makes them radiolucent to

x-ray imaging techniques. Attempts to render plastics radiopaque have

taken the following approaches: (1) incorporation of radiopaque metals

such a lead foil, gold or silver alloy, [2-4] (2) addition of heavy metal

salts such as barium sulfate, barium fluoride, barium acrylate, or bismuth subnitrate as fillers, [5-8] or (3) incorporation of an element

of relatively high atomic number into a silanized glass used as reinforcing filler of a composite resin, [9-12] (4) addition of

halogenated saturated or unsaturated compounds such as tetrabromoethane

or aliphatic bromoacrylates or methacrylates to the uncured resin.

[13,14] All these modifications have certain disadvantages. Addition of

metal or metal salts causes stress concentrations at the interface

between the insert and the resin which will weaken the materials and may

eventually result in fracture. It also lowers the mechanical properties

(transverse-, impact-, compressive- and tensile strength) . Translucency

of such radiopaque plastics is usually lower than those containing no

7
additives. Plastics with radiopaque glass ingredients are difficult to

polish. Resins with halogenated aliphatic ingredients discolor with time

and are unsuitable for many applications where esthetic characteristics

are important. The state of the art of radiopaque plastics for dental

applications has been reviewed. [1 , 2]

A desirable radiopaque plastic should have a homogeneous composition,

with excellent mechanical, thermal and optical properties and high

imaging characteristics so that its outline (including details) is

readily visible in various environments on minimum exposure to x-ray

radiation or ultrasonic waves. These properties should not deteriorate

on aging in the surrounding environment.

Introduction

At present, plastics used for most dental appliances and materials

including removable dentures and temporary crown and bridge materials are radiolucent. Radiopaque denture base materials combining adequate

physical and esthetic properties with ease of processing similar to the

well accepted radiolucent acrylic plastics are not available

commercially.

Monomers with a high percentage of atoms of high molecular weight such as pentabromophenyl or tniodophenyl methacrylate are compatible with methyl

methacrylate. [15] The pentabromophenyl methacrylate is commercially

available and the triiodo derivative has been synthesized in this

laboratory. The rate and kinetics of polymerization of monomer-polymer

dough is not altered greatly by the addition of these halogenated

compounds. Addition of 10 to 15 percent of the brominated monomer to

methyl methacrylate results in radiopaque polymers. Such compositions

are more homogeneous than filler containing compositions and have higher

strengths than commercial bone cements with barium sulfate [15]

.

Objective

To develop a clinically useful radiopaque denture resin based on halogenated aromatic methacrylate copolymers.

PROGRESS REPORT

Phase I. Using commonly accepted testing procedures, study the curing

characteristics, physical, chemical, esthetic and radiopaque properties

of self-curing denture base materials prepared from copolymers of

pentabromophenyl and triodophenyl methacrylate and methyl methacrylate

copolymers

.

Compositions containing 10% and 15% pentabromophenyl methacrylate

(PBPMA) or triiodophenyl methacrylate (TIPMA) in the liquid were mixed with commercial polymer powder. Resins with 15% halogenated

monomers showed good radiopacity. Water sorption or water

solubility of the cured resin was not changed on addition of

halogenated monomer. The PBPMA containing resin passed the color

3
stability test whereas material with TiPMA gave a perceptible color

change. Storage stability of liquids prepared with some batches of

PBPMA did not pass the 60 °C storage stability test.

To overcome this problem, poly(methyl methacrylate) (90%) - pentabromophenyl methacrylate (10%) suspension copolymer powder has

been synthesized in cooperation with Esschem. The radiopacity of

mixtures containing this copolymer exhibited satisfactory

radiopacity. Procedures to synthesize and characterize copolymers

with a higher concentration of PBPMA are under active

investigation.

Phase II. If properties of formulations studied in phase I pass all

requirements of the ADA/ANSI, specification for denture base resins,

have adequate working properties and good esthetic characteristics, then

determine the biocompatibility of the added monomer and of the cured

denture base copolymer resin.

Work on this phase may be initiated at a later date.

9
References

[1] Council on Dental Materials, Instruments and Equipment (prepared by G.M.

Brauer) . The Desirability of Using Radiopaque Plastics in Dentistry: A

Status Report. J. Am. Dent. Assoc. 102 347-349 (1981).

[2] Bursey, D.C. and Webb, J.S. Incorporation of Radiopaque Materials into

Denture Plastics. U.S. Armed Forces Med. J. 11 561-566 (1960).

[3] Atkinson, H.F. Partial Denture Problems: The Lack of Radio-opacity in

Methylmethacrylate. Aust. J. Dent. 58 349-351 (1954).

[4] Holden, M.H. The Radiolucent Plastic Foreign Body. Dent. Pract. Dent.

Rec. 18 209-211 (1968) .

[5] Alvares, L.C. Radiopacity of Acrylic Resins. Oral Surg. 22 318-324

(1966).

[6] Saunsbury, P. Radiopaque Denture Resins. Dent. Pract. 14 243-244

(1964)

.

[7] Combe, E.C. Further Studies on Radiopaque Denture Base Materials. J. Dent. 1 93-97 (1972) .

[8] Elzay, R.P. Pearson, G.O. and Irish, E.F. Clinical and Histologic

Evaluation of Commercially Prepared Radiopaque Denture Material. J. Prosthet. Dent. 25(3), 251-257 (1971).

[9] MacCulloch, W.T. and Stafford, G.D. Radiopaque Denture Base Materials.

Br. Dent. J. 131 22-24 (1971).

[10] Chandler, H.H., Bowen, R.L. and Paf f enbarger , G.C. Development of a Radiopaque Denture Base Material. J. Biomed. Mater. Res. 5 253-265

(1971).

[11] Chandler, H.H., Bowen, R.L. and Paf f enbarger , G.C. Physical Properties

of a Radiopaque Denture Base Material. J. Biomed. Mater. Res. 5 335-157

(1971).

[12] Chandler, H.H., Bowen, R.L. and Paf f enbarger , G.C. J. Biomed. Mat. Res.

5 245-251 (1971) .

[13] Molnar, J.E. (To COE Laboratories, Inc.) U.S. patent 3,715,331, Feb. 6,

1973 .

[14] Combe, E.C. Studies on Radiopaque Dental Materials. Dent. Pract. 22 51-

54 (1971)

.

[15] Brauer, G.M. , Steinberger, D.R. and Stansbury, J.W. Modified Radiopaque

3one Cement, with Low Exotherms. Biomaterials 84, Transactions, Vol. 7,

p.347.

10
D. Study of Adhesion and Adhesion Promoting Agents to Dentin

Overview

The main disadvantage of most dental restorative materials is the lack of

adhesive bonding to tooth structures in the oral environment. These

materials are kept in place solely by mechanical interlocking to the

cavity preparation. A restorative that chemically bonds to tooth

structure should inhibit the formation of secondary caries since it would

prevent percolation of microorganisms and liquids by sealing the marginal

areas of the restoration. With such a material, sealing of incipient

carious lesions could be realized. An adhesive cement could lead to less

invasive cavity preparations resulting in decreased loss of sound tooth

substance.

Introduction

Many procedures to obtain permanent bonding to enamel or dentin have been

suggested. Pretreatment of enamel with dilute acid enhances adhesion of

restorative resins to enamel, but this is contraindicated for dentin.

There are many constraints inherent in the long term bonding to dentin

[1-4] and the present adhesives have found limited clinical use for this

application. Surface grafting of monomers to mineralized tissues such as bone can be accomplished with persulfate [5] and to dentin with tri-nbutylborane oxide as initiator . [6 , 7] Zinc polyacrylates and glass

ionomer cements adhere to enamel but only weakly to dentin. Excellent

adhesion to dentin by acrylic resins is obtained with isobutyl 2-

cyanoacrylate , but the bond strength decreases on water exposure. [8] A

mixture of a phosphorus ester of 3IS-GMA and diluent monomer polymerizable by peroxide, tertiary amine and sulfinic acid salt has been

introduced commercially as a dentin-composite bonding agent. [9] Monomers

with hydrophobic and hydrophilic moieties such as 4-methacryloxyethyl

trimellitic anhydride (4-META) and the diadduct of hydroxyethyl

methacrylate and pyromellitic anhydride (PMDM) bond dentin to acrylic

resins . [10 , 11] Most effective are successive treatments of the dentin

surface with ferric oxalate, a 5 to 10 percent acetone solution of a glycine derivative (adduct of N-phenyl or N-p-tolylglycine and glycidyl

methacrylate) followed by a 5 percent solution of PMDM in acetone. [11]

Another good bonding agent to dentin is the mixture of 2-hydroxyethyl

methacrylate and glutaraldehyde . [12-14] Thus, investigations during the

last five years have developed luting agents that adequately bond to

dentin. Major disadvantages of the presently recommended dentin bonding

systems are (1) the tooth surface must undergo a number of pretreatments

which are time-consuming and may limit the clinical usefulness and cost

effectiveness of the process, (2) strict adherence to the protocol such

as removal of excessive monomer and water from the treated tooth surface

in the drying cycles of the most efficient procedure [11] are mandatory

to obtain optimum bonding, (3) the biocompatibility of the various

regents and compounds used in many of these tooth treatment procedures

has not been fully explored.

11
Objectives

Efforts, in this proposal, are directed to develop film-forming surfaces

that could serve as adhesives or sealants and to synthesize compounds and

formulations containing functional groups that are effective adhesion

promoters to mineralized tissues. Specifically these studies will (1)

determine the grafting efficiency of oligomers and polymers of isocyanatoethyl methacrylate having either functional isocyanate and

methacrylate groups with the aim of obtaining a durable polymer coating

on the dentin surface, (2) synthesize and evaluate the adhesive

properties of methacrylate esters from a homocylic tetracarboxylic

dianhydride which is closely related to the aromatic dianhydride, used to

prepare PMDM, and (3) study the forces needed to fracture cemented

surfaces and the relationship between retention of cemented crowns and

the film thickness of the cement layer.

PROGRESS REPORT

Phase I. Synthesize and evaluate adhesive properties of oligomers of 2-

isocyanatoethyl methacrylate or other isocyanate containing monomers to

dentin.

Phase la. Synthesize oligomers with pendant isocyanate groups.

2-Isocyanatoethyl methacrylate (IEM) and m-isopropenyl-0 , (S- dimethylbenzyl isocyanate (TMI) (Fig. 1) are difunctional monomers

with reactive isocyanate (NCO) groups and a polymerizable vinyl

double bond. Reactions with either function can be carried out

independently of the ocher group.

Oligomers (low molecular weight) polymers were synthesized using

IEM, TMI, ethyl acrylate (EA) , butyl methacrylate (3MA) or hydroxyethyl methacrylate (HEMA) as shown in Fig. 2. Liquid

products resulted after evaporation of the solvent. Monomers used

in the preparation of the respective oligomers, mole ratios of monomers used, and refractive indices, no, of the liquid products

are given in the following table.

12
MONOMERS WITH ISOCYANATO GROUPS

H C

2

cA

0

II C-C-O-CH -CH -N«C«0

2 2

2- Isocyanatoethvl methacrylate

I EM m-Xsopropenyl-® ,«=dime thy 1 benzyl Isocyana'

m-TMI

FIGURE 1

CHch

3

c - coch

2 ch2 nco

6

1 % 2 ,2^ -Azobi s~

i sobutyroni tri 1

e

in 2-Ethoxyethy

1

acetate at 120°C

Synthesis of poly (alkyl methacrylates)

with pending Isocyanate groups

CH- i o

c~~

c=o I 0

CH- 1 2

CH

N

ii C

ii o

2

CH

C

3

C^O I 0

CH- 1 2

?

H

2

N

II c

II O

cn2

2

CH3 C-COCH

2 CH2 NCO + HO- R

6

Dibutyl tin

dilaurate

CATALYST

in CH 0 C1 9

Synthesis of urethane methacrylate monomers

R

i 9

c=o

NH

ch2

ch2

o

c=o

C-CHii 0

ch2

13

FIGURE 2
MONOMER USED IN PREPARATION OLIGOMERS

Oligomer Mole Ratio of Resnective Monomer

no 23

of Oligomer

IEM-EA 1:1.5 1.4719

IEM-BMA-EA 1:1. 3:1.

8

1.4593

TMI-EA 1:2 1.5065

TMI-BMA 1:1.4 1.5161

IEM-SA-TMI 1 . 3 : 1 :

1

1.5083

IEM-BMA-TMI 1.8:1. 4:1 1.5055

Infra-red analysis of the oligomers confirmed the presence of the

isocyanate groups. Idealized structures of TMI-3MA and IEM-BMA-TMI

are given in Fig. 3. The urethane methacrylate of IEM or TMI with

hydroxyethyl methacrylate were prepared at room temperature under

the conditions outlined in Fig. 2.

Gel permeation chromatograms indicated that most of the TMI-BMA and

IEM-BMA-TMI were a low molecular weight materials. Only a small

fraction of the copolymers had an elution volume below 42, which

for the polystyrene reference material would indicate a molecular

weight of 1748. A trimer of IEM was also synthesizsed (MP = 77-78

°C, yield 69%)

.

Phase lb. Prepare adhesive formulations and evaluate their properties.

Only formulations with isocyanate groups (not urethanes) in the

side chain adhered to mineralized tissues whereas the urethanes or IEM trimer did not react directly with bone. Bone powder reacted

at room temperature within three hours with IEM-EA or IEM-BMA-EA in

the presence of dibutyltin dilaurate or triethyl amine. Dentin

powder did not react with IEM-BMA-EA, in the presence of catalysts,

but reacted at 42 °C with IEM-EA or IEM.

These experiments indicated that pretreatment of the mineralized

tissue may improve bonding. The use of 5% to 25% aqueous

glutaraldehyde solution suggested by Munksgaard and Asmussen [15—

19] in combination with isocyanate containing formulations followed

by application of a typical bonding agent based on BIS-GMA and

triethylene glycol dimethacrylate greatly improved adhesion.

Shear and tensile strength of bone (conducted under another

project) cemented with various adhesive compositions are given in

Tables 1 and 2.

14
Shear strength of all isocyanate containing monomers and oligomers

was very high. Maximum relative shear strength (54.1 kg load) was obtained with the IEM-BMA-TMI copolymer. The Gluma adhesive after

ethylenediaminetetracactitic acid EDTA pretreatment of the bone

also yielded a strong bond, but the ferric oxalate-NPG-PMDM

procedure resulted in a weaker joint. Tensile adhesion after 24

hours storage in water was highest for the I EM (9.9 MPa) monomer.

The TMI-BMA or IEM-BMA-TMI compositions had significantly higher

bond strength than bone cemented with Gluma or butyl 2-

cyanoacrylate. After 7-day therocycling between 5 °C and 55 °C the

TMI-BMA oligomer adhesive had a tensile adhesive strength of 7.9

MPa. Thus, exposure to water and thermal shock produced no deterioration of the bond. For the other compositions the loss in

bond strength is small compared to that experienced by butyl or other 2-cyanoacrylates . [8] All of the tensile strength specimens

broke cohesively.

For dentin bonding, bovine dentin was cemented to a composite

slurry placed into the recessed tip of a cylinder used in the

static load testing procedute of Lee et al. [20] Generally, bond

strength values after 24 hour storage of the joint in water were

low. Results given in Table 3 show that cementation with IEM-BMATMI copolymer or IEM produced stronger joints than those obtained

with GLuma or NPG-PMDM. (Table 1)

The bond strengths of pretreated human dentin joined to composite

with various adhesives as measured by the more elaborate procedure

suggested by Bowen is given in Table 4. These values were considerably higher than those obtained for bovine dentin using the

procedure of Lee.

The lower bond strength of bovine dentin compared to human dentin

may have been caused by the better bonding of the adhesive to the

latter substrate. The higher bond strength values may result from

the more thorough preparation of the flattened dentin surface and

the better contact at the tooth-adhesive and the adhesive-composite

interface in the technique employed for cementing human dentin to

composite. A slight increase in adhesion occurred after

purification of the oligomer by extraction with 35% hexane-15%

ethyl acetate which removed residual monomer. Neither the

difference in bond strength of dentin to NPG-PMDM, purified IEMBMA-TMI or Gluma was statistically significant.

The suggested mechanism for the adhesion of aldehyde treated

mineralized tissues to isocyanate monomers is shown in Fig. 4.

A survey of the available toxicity data for the monomer indicates

that they may not be suitable for clinical applications. However,

oligomers with TMI posses no residual isocyanate containing

monomer. Molecular weights and concentration of isocyanate groups

are adjustable. The oligomeric liquids have low volatility and

should not diffuse readily into tissues, but their biocompatibility

15
as adhesives to mineralized tissues will have to be established.

Conclusions

Monomers and low M.W. liquid copolymers containing pendant

isocyanate groups form stronger, more permanent, water-resistant

bonds to glutaraldehyde treated bone than other adhesives. The

isocyanate group containing compositions should also be studied

further as potential dental adhesives.

This work was presented at the IADR and American Chemical Society

meetings. ,

Phase Ic. If studies conducted in Phase la and lb are successful,

initiate cooperative projects to study biocompatibility of these adhesive

systems and their application in dental practice.

Although the adhesives prepared in phase lb have not been

completely characterized or optimum desirable properties have been

determined, investigators at two universities (South Carolina,

Missouri) have expressed an interest to conduct studies of the

toxicological properties.

Phase II. Synthesize the dimethacrylate ester of 5- (2 , 5-dioxotetrahydrof uryl) -3-methyl-3-cyclohexene-l , 2-dicarboxylic anhydride and

determine its adhesion to dentin.

This dimethacrylate having a more non-polar homocyclic nucleus

compared to the aromatic groups in 4-META or PMDM was synthesized

at room temperature with hydroxyethyl methacrylate in CH2 CI2 and

dimethylaminopyridine accelerator. The slightly yellow viscous

product adhered well to ferric oxalate treated bone and composite.

The bond strength appeared to be lower than that of the isocyanato

containing oligomers (phase I). Thus, investigation with the

oligomers described in phase I was emphasized during this period.

Phase III. Study the effects of film thickness on the retention of

cements

.

Film thickness (FT) and retention of zinc phosphate,

polycarboxylate and lonomer cements as a function of powder-liquid

(P/L) ratio was determined for both nonvented and vented crowns using the parallel plate specification test. FT increased with the

P/L ratios especially at high cement consistencies. Cementation of

vented crowns yielded thinnest FT usually followed by that obtained

by the parallel plate method and the nonvented crown.

The effect of P/L ratio on FT or retention was more dependent on

the composition of the brand than on the type of cement. For some polycarboxylate or ionomer cements retention decreased with

increasing film thickness. Little retention of well-fitted crowns

was found for zinc phosphate powder-water mixes as suggested

16
previously. [21]

The P/L ratios suggested in the manufacturer's instructions did not

always yield the maximum retention for either vented or unvented

crowns. Venting of prepared crowns is indicated since this

procedure usually increased their retention and was much less

dependent on variations in P/L ratios.

17
IDEAL! ZED STRUCTURE OF COPOLYMERS STUDIED

where

MECHANISM OF ADHESION OF COLLAGENOUS SURFACES

TO ISOCYANATE CONTAINING MONOMERS

* , Mir • -f iv ciio y

n-cHoii

polymeric bond

t f^NCO

v

Initiator * ^

R-y

R-CHONllCOn

1

R “

1 H C

2

If C-C

Cl\

FIGURE 4

18
TABLE

RELATIVE SHEAR STRENGTH OF BONE CEMENTED WITH VARIOUS

Adhesive Breaking Load „

IEM 42.1 ± 3.5

TMI 41 .8 ± 6.1

TMI *- BMA 40.7 ± 5.3

IEM - EA - TMI 41.0 ± 4.5

IEM - BMA ~ TMI 54.1 ± 9.4

Gluma 43.0 ± 13.3

FeOx - NPG - PMDM

b

21 .9 ± 4.0

Blank 6.0 ± 4.7

a Mean of 10 specimen (bonding area: 1 cm x 1 cm) after 24 hour

storage in ^O.

b Ferric oxalate-N-phenylglycine-dimethacryloxyethylpyromellitic acid

TABLE 2

TENSILE STRENGTH OF BONE CEMENTED WITH VARIOUS ADHESIVES

Bond Strength in MPaa after storage in H

2 O for

Adhesive 24 h. at 23 °C 7 d. - thermocycled

IEM 9.89 ± 1 .44 7.41 ± 1 .17

TMI 9.03 + 1 .79 8.38 ± 2.25

TMI - BMA 7.94 ± 1 .19 7.92 2.21

IEM - BMA - TMI 8 . 60 ± 1.17 7.47 ± 2.15

Gluma b 7.14 ± 1 .30 6.98 X 0.93

Isobutyl cyanoacrylate 6.62 ± 1 .73 4.52 ± 0.46°

Control 1 .07 + 0.61 2.75 0.31

k Mean of 10 specimens or those not fractured within the bone.

EDTA - glutaraldehyde - hydroxyethyl methacrylate

C one day d

5 °C and 55 °C

19
TABLE 3

TENSILE STRENGTH OF BOVINE DENTIN BONDED TO COMPOSITE

Dentin was treated with 255 -aq. glutaraldehyde prior to

application of adhesive solution. Freshly nixed composite

was then applied.'.

Adhesive Bond Strength after 24 h In HgQ, MP a a

IEM 4.27 ± 2.22

TMI 2.53 4d

cm* 9 0

* o

TMI - BMA «

ao o 1 ± •

UJ

IEM - BMA - TMI 4.51 ± 1 .70

Gluma 1.83 1.22

NPG - PMDMb 2.08 * 1.42

Blank 0.25 ± 0.27

a Mean of six specimen

b Ferric oxalate - N-phenylglycine-dimethylacryloxyethyl

pyromellitic acid. .

TABLE 4

TENSILE STRENGTH OF HUMAN DENTIN BONDED TO COMPOSITE

Dentine was treated with 0.5M EDTA and 55 glutaraldehyde. A 55

solution of the adhesive in CH 2ci 2 was applied, followed by

application of bonding resin and composite.

Adhesive Bond Strength after 1 4 hr in H-, p. MPaa

I EM

TMI

TMI-BMA

IEM-3MA-TMI

IEM-BMA-TMI b

Gluma

NPG-PMDM

Blank

7.03 ± 1 .51

7.47 i 2.11

5.55 ±1.96

6.53 ± 1.52

7.58 ± 1 .91

7.1.7 ±1.87

8.51 ± 3.09

1.37 ± 1.02

a Mean of five specimen

b Purified by extracting twice with 855 hexane-155 ethyl acetate

20
References

[1] National Institute of Dental Research: Adhesive Restorative Dental

Materials-II. Public Health Service Publication No. 1494, U.S. Govt.

Printing Office, Washington, DC (1966) .

[2] Brauer, G.M. The Chemistry of Biosurfaces. M.L. Hair, ed. Vol. 2,

Marcel Dekker, NY, NY, p. 731-300 (1972).

[3] Brauer, G.M. Scientific Aspects of Dental Materials. J.A. von Fraunhofer, ed., Butterworths , London, p. 49-96 (1975).

[4] Causton, B.E. Biocompatibility of Dental Materials, D.C. Smith and D.F.

Williams, ed. Vol. II, p. 125-141, CRC Press, Inc., Boca Raton, FL

(1981) .

[5] Brauer, G.M., Termini, D.J. and Levy, S.M. J. Dent. Res., 56 646-659

(1977).

[6] Sanjo, D. J. Dent. Res., 50 60 (1971).

[7] Miura, F., Nahagawa, K. and Mashara, E. Am. J. Orthod., 59_ 35 (1971).

[8] Brauer, G.M., Jackson, J.A. and Termini, D.J. J. Dent. Res., 5J3 1900-

1907 (1979).

[9] 3M Dental Products Department, Pamphlet, Scotchbond Dental Adhesive

System (1982).

[10] U.S. Patent, 4,148,983 (April 10, 1979), E. Masuhara, N. Nakabayashi and

J. Takeyama (to Mitsui Petrochemical Industries Ltd.).

[11] Bowen, R.L., Coble, E.N. and Rapson, J.E. J. Dent. Res., 61 1070-1076

(1982).

[12] Munksgaard, E.C. and Asmussen, E. Bond Strength Between Dentin and

Restorative Resins Mediated by Mixtures of HEMA and Glutaraldehyde . J. Dent. Res. 63 1087-1089 (1984).

[13] Munkgaard, E.C., Itah, K. and Jorgensen, K.D. Dentin-Polymer 3ond in

Resin Fillings Tested in vitro by Thermo and Load-cycling, J. Dent. Res.

64 144-146 (1985)

.

[14] Hansen, E.K. and Asmussen, E. Comparative Study of Dentin Adhesives.

Scand. J. Dent. Res. 93 280-287 (1985).

[15] Munksgaard, E.C. and Asmussen, E. J. Dent. Res. 63 1087-1089 (1984)

.

[16] Munksgaard, E.C. and Asmussen, E. Scand. J. Dent. Res. 93 463-466 (1985).

[17] Hansen, E.K. and Asmussen, E. Scand. J. Dent. Res. 9_3 280-287 (1985).

21
[13] Munksgaard, E.C. Irie M. and Asmussen, E. J. Dent. Res. 64. 1409-1411

(1985) .

[19] Munksgaard, E.C. Itoh, K. and Asmussen, E. and Jorgensen, K.D. Scand. J. Dent. Res. 93 377-380 (1985).

[20] Lee, L., Swartz, M.L. and Culp, G. J. Dent. Res., 48 211-216 (1969).

[21] Paf f enbarger , G.C., Sweeney, W.T., and Isaacs, A. Zinc phosphate

cements: physical properties and a specification. JADA 21 1907-1924

(1934) .

Publications

Brauer, G.M. and Antonucci, J.M. Dental Applications (of Polymers),

Encyclopedia of Polymer Science and Engineering. Wiley-Interscience , New York,

NY 2nd ed., Vol. V, pp 698-719 (1986).

Brauer, G.M. and Stansbury, J.W. and Flowers, D. Modification of Cements

Containing Vanillate or Syringate Esters. Dent. Mat. 2 21-27 (1986).

Brauer, G.M., Steinberger, D.R. and Stansbury, J.W. The Effect of Inhibitors,

Accelerators, Cross-linking Agents and Monomers on the Properties of Bone

Cement. J. Biomed. Mat. Res. 20 839-852 (1986).

Manuscripts Under Review or Accepted for Publication

Iizuka, H., 3rauer, G.M., Rupp, N., Ohashi, M. and Paffenbarger G. Forces

fracturing cements at die interfaces and their dependence on film thickness.

Submitted to Dent. Mat.

Brauer, G.M. Color changes of composites on exposure to various energy

sources. Editorial Review.

Invited talks

Brauer, G.M. Adhesive Cements and Intermediate Restorations Containing

Vanillate or Syringate Esters. G.M. Brauer, Lunch and Learning Session, IADR

meeting in The Hague, 1986.

Contributed talks

Iizuka, H., Brauer, G.M., Rupp, N. , Ohashi, M. and Paffenbarger, G. Film

Thickness and Forces Fracturing Cements at Die Interfaces. AADR meeting 1986.

Slew, C., Gruninger, S.E., Brauer, G.M., and Tesk, J. Biological Safety

Evaluation of Syringic Acid Ester Cements. AADR meeting 1986.

Lee, C., Brauer, G.M., and Stansbury, J.W. Copolymers of 2-Isocyanatoethyl

Methacrylate or m-Isopropenyl-fl , |3-dimethylbenzyl Isocyanate-Synthesis and

Adhesive Properties. IADR meeting, The Hague, 1936.

22
Brauer, G.M. and Lee C. Adhesion of 2-Xsocyanatoethyl methacrylate, misopropenyl-fS , 3-dimethylbenzyl isocyanate or their Copolymers to Bone. MidAtlantic Regional Meeting, American Chemical Society, Baltimore, MD, Sept.

1986.

23
Monomers which Polymerize with Expansion

Overview

A great deal of attention in recent dental composite research has been

focused on the problems of polymerisation shrinkage and adhesion. To a large extent, the difficulties encountered in bonding composite to tooth

structure can be attributed to the polymerization shrinkage. 1 Other

deficiencies such as marginal gap formation, which may lead to

hypersensitivity2 and secondary caries3

, as well as micro-defects in the

resin matrix, which may cause accelerated degradation, have also been

linked to the problem of polymerization contraction.

Our effort in this area has centered on the formulation of spiro

orthcarbonate monomers, which expand in volume during polymerization,

with conventional monomers that contract. The resulting formulations

should minimize polymerization shrinkage and many of the problems

associated with it including limitations on the formation of strong,

durable adhesive bonds to dentin and enamel.

PROGRESS REPORT

Phase I. Synthesis of spiro orthocarbonate monomers capable of freeradical polymerization with an expansion in volume.

Several new spiro orthocarbonate (SOC) monomers have been prepared

with the basic idea of increased reactivity in mind. New methods

were devised to allow the formation of fused five and six-membered

rings as seen in monomers 1 and 2 which were recently synthesized.

With an exocyclic double bond located on the five-membered ring,

the monomer ring-opens by a different mechanism than that observed

for six and seven-membered rings in which the double bond is not

adjacent to one of the spiro-oxygens. These monomers are more reactive in free radical polymerization by virtue of steric factors

as well as the different ring opening process. Monomer 2 was synthesized to directly compare the effect of double bond placement

on the relative reactivities of the double bonds.

Another effort to achieve more energetic SOC monomers has resulted

in the synthesis of the highly reactive compound 3.. This monomer containing an acrylate-like double bond has been prepared, but not

yet successfully isolated due to its reactivity.

1 2
Another SOC monomer 4 with a very bulky substituent on one of the

rings has been synthesized.

4

This monomer was designed to have a relatively high melting point

and to provide a high modulus to copolymers in which it is

incorporated. Further, the isobornyl group acts as a very

efficient hydrophobic barrier around the moisture sensitive tetra=

oxaspiro linkage.

Phase II. Polymerize and characterize the monomers synthesized in Phase

I.

The homopolymerization of several of the previously prepared SOC monomers has been achieved. The monomers (1 and 2) containing the

unsaturated f ive-merabered ring have been polymerized to fairly high

molecular weight by di- tert- butyl peroxide (DTBP) at 120 °C.

Polymers of 1 are powdery solids which are soluble in chloroform

while polymers of 2 are slightly elastic, insoluble cross-linked

solids. The more reactive monomer 3 underwent spontaneous thermal

polymerization during an attempted vacuum distillation. Other SOC monomers have been polymerized to low molecular weight oligomers by

either DTBP at 120 °C or BF3~0Et2 at 0 °C. These monomers do

copolymerize with conventional acrylate-based monomers under a variety of free radical polymerization conditions.

Phase III. Formulate dental composites and adhesives based on monomers

obtained from Phase I.

There appear to be two formulation techniques which take best

advantage of the polymerization expansion of these SOC monomers.

First, the liquid SOC's or those that melt just above room temperature, can be used to entirely replace the conventional

diluent monomers used with BIS-GMA-based formulations. The

favorable results obtained in this way can be rationalized by the

fact that the conventional diluent monomers, such as TEGDMA,

exhibit the greatest degree of polymerization shrinkage in these

systems. Therefore, it is most practical to replace this type of monomer with a SOC monomer which can expand and still serve the

function of a reactive diluent for the BIS-GMA.

A second useful formulation technique involves adding one of the

higher melting, crystalline SOC monomers to a conventional dental

resin mixture. Polymerization of the resulting reactive slurry at

25
slightly elevated temperatures leads to the SOC melting,

accompanied by a large volume increase, and then undergoing ringopening copolymerization with an additional volume expansion.

Phase IV. Evaluate the physical properties of polymers derived from the

formulations prepared in Phase III.

The SOC monomers can copolymerize with other monomers using visible

light activation; however, slightly higher DTS results were consistently obtained from the chemically cured systems.

Paralleling this was the finding that a dual cure (normal photocuring accompanied by a slow chemical cure) system gave less

polymerization shrinkage and higher mechanical strength than a photo-cure alone. This seems to indicate that the less reactive

SOC's require a longer-lived source of free radicals to bring about

efficient ring-opening of these monomers.

The following results were obtained when SOC monomers were substituted for TEGDMA in a BIS-GMA based dental composite resin

formulation. Polymerization shrinkage was reduced by 31 percent

compared to the control formulation. Enhancing the degree of

conversion Jay using the dual cure technique resulted in less

polymerization shrinkage for the SOC containing formulation while

the control resin showed the expected increase in contraction with

the greater degree of cure. The tensile adhesive strength of the

experimental composite resin was approximately 250 percent greater

than that of the control after the specimens of composite bondedto-polished stainless specimens were stored 24 hours in 37 °C

water.

Phase V. Biocompatibility testing of formulations selected on the basis

of results from Phase IV.

Biocompatibility testing in the form of implantation

toxicity studies have previously been conducted with a dimethylene substituted spiro orthocarbonate monomer4

. The results indicated that the ring-opened polymer as well as a mixture of BIS-GMA and the spiro monomer

illicit only mild inflamatory responses which are characteristic of a wide range of dental materials. No

testing of the more reactive spiro monomers described

here has yet been carried out. If the physical

properties of formulations containing these new monomers demonstrate the expected advantages, then a new series of biocompatibility tests would be in order.

26
References

[1] Hansen, E.K. Effect of scotchbond dependence on cavity cleaning,

cavity diameter and cavosurface angle, Scand. J. of Dent. Res. 92 . 141-147, (1984).

[2] Brannstrdm, M. Communication between the oral cavity and the dental

pulp associated with restorative treatment, Operative Dentistry 9,

57-68, (1984).

[3] von Fraunhofer, J.A. and Hammer, D.W. Microleakage of composite

resin restorations, J. Prosthetic Dent. 5JL., 209-213, (1984).

[4] Thompson, V.P., Williams, E.F. and Bailey, W.J., Dental resins with

reduced shrinkage during hardening, J. Dent. Res. 58 . 1522-1532,

(1979).

Publications

Brauer, G.M., Steinberger, D.R. and Stansbury, J.W. Dependence of curing time,

peak temperature and mechanical properties on the composition of bone cement,

J. Biomed. Mater. Res. 20, 839-852 (1986).

Contributed Talks

Stansbury, J.W. and Bailey, W.J. Synthesis of monomers that polymerize with

expansion in volume, AADR meeting (1986).

Antonucci, J.M., Stansbury, J.W. and Venz, S. Synthesis of silyl ether

derivatives of BIS-GMA, AADR meeting (1986).

Lee, C. , Brauer, G.M. and Stansbury, J. W. Copolymers of 2- isocyanatoethyl

methacrylate or m-isopropenyl -a, a- dimethyl (benzyl isocyanate- synthesis and

adhesive properties, IADR meeting (1986).

27
F. Improvement of Dental Composites, Sealant Cement and Adhesive Materials

Overview

The quest for a durable, esthetic, adhesive and biocompatible material

suitable for the restoration of lost tooth structure has long challenged

dental materials researchers . A significant step toward the realization

of this goal was the development of resin based dental composites which

overcame many of the shortcomings of the silicate cements (purely

inorganic composites) and unfilled resin restoratives (purely organic

composites based on methyl methacrylate and its polymer) . The synthesis

of BIS-GMA (an offspring of the marriage of epoxy and acrylate chemistry)

by Bowen, ushered in the modern era of resin based dental composite

restorative materials and also other resin based dental materials [1,2].

The essential components of dental composites are: (1) a resin system

comprising one or more vinyl monomers which on polymerization forms the

matrix or continuous phase, (2) reinforcing fillers such as silanized

glass, quartz, other ceramics, organic and hybrid organic-inorganic

powders of various sizes and shapes which constitute the dispersed phase,

(3) an interfacial phase for bonding the continuous and dispersed phases,

derived from vinyl silanes, titanates, i.e., coupling agents, (4) a polymerization initiator system effective under ambient conditions, and

(5) stabilizers for optimizing storage stability and also preserving the

chemical stability of the hardened restoration. Unlike glass ionomer

cements which bond to tooth structure, current resin based composites are non-adhesive in nature [3,4].

However, the acid-etch technique (Buonocore) , in most situations,

provides an effective micromechanical mechanism for bonding dental

composites to enamel [5,6]. Bonding to dentin is a more challenging

problem but recent developments appear to be yielding effective coupling

agents for this substrate as well [7-16] . Efforts to enhance the

durability and range of applications (e.g., posterior as well as anterior

fillings) of dental composites include optimization of the types, sizes,

shapes and volume of the dispersed phase, reductions in the solubility

parameter, residual vinyl unsaturation and polymerization shrinkage of

the resin phase, and the development of more effective interfacial

bonding phases.

Dental sealants have similar compositions and chemistry but are unfilled

or only lightly filled and usually contain a higher proportion of diluent monomer (s). Dental resins also are widely used in other applications

(e.g., adhesives , core build-up and crown and bridge materials, laminating

vaneers , etc. )

.

Dental cements, which also have a composite nature, find use in a wide

variety of dental applications. In restorative dentistry they are employed as temporary, intermediate, and (in the case of glass ionomer

cements) permanent filling materials. Their chemistry of hardening

involves a series of acid-base reactions involving ion-exchanges that

result in the development of a matrix into which are imbedded partially

reacted basic filler particles [3]

.

An ion-exchange mechanism involving

28
polyelectroylte cements (e.g., glass ionomer) and mineralized tissue also

may explain their adhesion to tooth structure [4]

.

Two types of dental cements can be distinguished depending on their water

content: (1) those that are aqueous based (e.g., zinc phosphate,

polycarboxylate, glass ionomer) and in which water plays a role both in

their setting and in the development of their molecular and micro

structures, and (2) those that are relatively non-aqueous in nature,

although catalytic amounts of water or other protic compounds (e.g.,

acetic acid) are needed to achieve clinically acceptable setting times

(e.g., ZOE, EBA, HV-EBA, dimer acid, etc.)

' This section is divided into four distinct parts:

I. Improvement of Dental Resin Systems for Composites and Sealants.

(Synthesis, Formulation and Evaluation)

II. Improvement of Dental Cements.

(Synthesis, Formulation and Evaluation)

III. Improvement of Interfacial Bonding Systems and Fillers for

Composites and Cements. (Filler Portion of Project is New)

(Synthesis, Formulation and Evaluation)

IV. Bonding of Low Surface Energy Resin Systems to Tooth Structure.

(New Project) (Synthesis, Formulation and Evaluation)

I. Improvement of Dental Resin Systems for Composites and Sealants

Objective

The goal of this research task is to enhance the durability of

dental composite, sealant, cement and adhesive materials through

the use of low-shrinking, but highly thermosetting hydrophobic

resins.

Background

Recent research has indicated that the oral environmental

resistance (OER) of resin based dental materials is a significant

factor in determining their in vivo performance and ultimate

service life both in relatively stress-free as well as in stressbearing applications [17-19] . The continual sorption of water and

other intraoral substances can promote plasticization of the

organic matrix, which can be viewed as the first line of defense of

composites and related resin based dental materials against the

constant assaults of the oral environment. Ultimately, this

chemical softening process can lead to degradation reactions not

only in the polymeric binder and critical interfacial phase but, in some cases, even in the filler phase as well [20-23]. Two related

approaches have been initiated in our laboratories as methods to

enhance the OER of these materials. One involves the use of

hydrophobic resin systems that have solubility parameters lower

than that prevalent in the oral environment [24,25]. The other is

aimed at increasing the degree of polymerization and the crosslink

29
density of resin systems by methods compatible with the clinical

situation [26-29] . The first approach involves the synthesis and

formulation of resins that yield polymers containing significant

amounts of fluorocarbon or siloxane segments to confer on dental

materials the necessary hydrophobicity (by lowering solubility

parameters) to resist the detrimental effects of the oral

environment [24,25,30,31]. The second approach, which also may

complement the first approach, involves the synthesis and

formulation of multifunctional methacrylates, multifunctional chain

transfer agents and other types of network forming agents that can augment the degree of cure and crosslink density [27-32] . Emphasis

also is directed to monomers that should have minimal

polymerization shrinkage [32] . An ancillary part of this approach

also involves the development of more efficient, color stable

initiator systems for ambient polymerizations of dental resins in a more uniform fashion [27] .

PROGRESS REPORT

Phase I

(a) Synthesis of oligomeric multifunctional monomers of higher

covalent fluorine content, lower viscosity and greater

flexibility.

This part of Phase I will commence next year.

(b) Formulation and evaluation of PFMA (Fig 2) and PFUMA (Fig 1)

based composites.

A visible light polymerizable composite formulation was prepared using the polyf luorinated prepolymer multifunctional

urethane methacrylate, PFUMA, and a siloxane diluent monomer,

BIS-MPTMS (Fig. 1) . A fine (2-4 0 m) fused, silanized quartz

powder was used as the reinforcing filler and camphorquinone

,

CQ, and ethyl 4-dimethylaminobenzoate , 4EDMAB, were used as the photoinitiator system (Table 1) . A second hydrophobic

composite derived from the polyf luorinated prepolymer

multifunctional methacrylate, PFMA, and the hydrocarbon

dimethacrylate diluent, DMDMA (Fig. 2) was prepared using the same filler and photoinitiator system (Table 1) . The wear properties of preconditioned specimens of these composites

are described in Part II, section A, (Page 60) of the report.

30
Table 1

COMPOSITION OF HYDROPHOBIC, FLEXIBLE

RESIN BASED COMPOSITES

Formulation Component Weight Percent

PFUMA 22.03

BIS-MPTMS - Resin 9.44

CQ 0.05

4-EDMAB 0.22

Silanized Filler 68.26

Fused Quartz

(2-4 0 m)

PFMA 21.69

DMDMA 9.04

CQ 0.05

4-EDMAB 0.20

Silanized 69.02

. Fused Quartz

(2-4 0m)

The task on new types of binary and tertiary diluent monomer

system is deferred to a later date.

(c) Syntheses of highly fluorinated multifunctional methacrylates

based on hexachlorocyclophosphazene. This part of the

project is deferred until a later period, depending on the

outcome of (a) and (b)

.

(d) Silyl ether derivatives of BIS-GMA

Previously, we reported the synthesis of a low viscosity,

bulky tetramethacrylate derived from BIS-GMA and 3-methacryloxypropyldimethylchlorosilane (MAPDMCS) (Fig. 3) . An

alternate route to this digilyl ether derivative of BIS-GMA

involves the use of 3-methacryloxypropyldimethylethoxysilane

(MAPDMES) in place of MAPDMCS. Infrared and NMR analyses

confirm the assigned structure.

Oligomeric silyl ether derivatives of BIS-GMA were prepared

using the synthetic routes outlined (Figs. 4 and 5)

.

The tacky, viscous resin was characterized by IR and NMR

analyses. Preliminary studies indicate that these silyl

ether derivatives are compatible with themselves as well as a wide range of dental monomers and yield composites with

acceptable mechanical properties (Table 2) . The water

sorption of these composites is expected to be lower than

31
BIS-GMA composites. The water uptake of the composite

derived from formulation 2, Table 2 was only 0.22 mg/cm2

. A more detailed account of this study was presented at the 1986

AADR meeting.

Table 2

24 HOUR DIAMETRAL TENSILE STRENGTHS OF

EXPERIMENTAL SILYL ETHER COMPOSITES

Diametral Tensile

Comnosite

Resin

ComDosition

PhotoInitiator

Powder

Liquid

Ratio

Strength in

Standard Dev:

(No. of Spec:

1 BIS-GMA/ (MAPDMS) 2 0.2 % CQ 6 42 + 2 0.7 % 4-EDMAB (5)

2 BIS-GMA/TMDSE 71% 0.15% CQ 4 35 + 2 HMDMA 29% 0.8 % 4-EDMAB (5)

3 BIS-GMA/TMDSE 57.3% 0.15% CQ 5 42 + 4 HMDMA 42.2% 0.8 % 4-EDMAB (5)

4 BIS-GMA 48.5% 0.15% CQ 5 43 + 1 3IS-GMA/ (6)

MAPDMS) 2 48.5% 0.75% 4-EDMAB

MAPDMES 3.0%

(e) Synthesis of hydrophobic urethane derivatives of BIS-GMA is

deferred until next year.

(f) Additives to increase the degree of polymerization and

crosslink density. Work in this area is deferred pending

completion of related project (g)

.

(g) Improved initiator systems for dental resins. Visible light

activated composites polymerize by a light induced reaction

involving a photoxidant, e.g.„ camphorguinone (CQ) and a photoreductant , e.g., a tertiary amine. This study was undertaken to determine some of the factors that may

influence the degree of cure (DC) , depth of cure (DOC) , and

degree of discoloration (DOD) of resin based dental

materials. The parameters that were evaluated for their

effect on these properties were (1) concentration of CQ, (2)

type and concentration of tertiary amine and (3) molar ratio

of amine to CQ. For this study the same visible light source

was used. DC was measured by FTIR methods. DOC composite

specimens were prepared by 10s irradiation from one side of

steel cylindrical molds. After the uncured portion was

32
removed, the hardened portion was measured by a micrometer.

DOD was determined visually after 24 hours exposure to a S275

sunlamp.

It was found that tertiary aromatic amines generally yield

composites with higher DC’s, DOC’s and DOD's than tertiary

aliphatic amines. For aromatic amines, the DOD depends on a number of factors, e.g., the amine concentration, the nature

and position of substituents, and the duration of the

exposure to the curing light. Increasing the concentration

of CQ increases DC and DOC, while increasing amounts of

tertiary amine have less effect on these properties.

In a related study, amine salts, derived from tertiary amines

and certain acids (oxalic, pyruric, benzoylf ormxc) and

complexes, arising from the interaction of these amines and

esters of the above acids as well as by their reaction with

aliphatic or aromatic anhydrides, were assessed for their

accelerative potential. In chemical cures using benzoyl

peroxide the amine salts and complexes derived from tertiary

aromatic amines were at least comparable in accelerative

potential (determined by setting time, diametrial tensile

strength) to their amine precursors and yielded composites

with superior esthetics and color stabilities. Similarly

these amine derivatives are effective, color-stable

photoaccelerators for resin systems containing CQ and/or • similar photooxidants. Thus, in addition to yielding resin

based materials with high DC's and DOC, the amine salts and

complexes provide cured materials of enhanced color

stability. Significantly, some of these amine derivatives

also can function as photoinitiators under appropriate

irradiation (e.g., sunlight, UV)

.

Phase II. Prototype Composite for Clinical Evaluation

A chemically activated, power/liquid, PFMA composite

formulation using a conventional fused quartz filler is being

evaluated by Dr. Joseph Moffa of USADA.

Phase II Composites derived from Phase I, (b) e.g., PFTJMA and

PFMA with several types of diluent monomers have been

evaluated for their mechanical properties (found to be at

least adequate) , water sorption (found to be extremely low)

oral environment resistance (found to be highly resistant to

the water end of the solubility parameter range, less so to

the heptane-alcohol region) , wear resistance (found to be

less subject to environmental factors) and polymerization

shrinkage (found to be low)

.

33
II. Improvement of Dental Cements

Overview

Although used in relatively small quantities, dental cements are essential in a number of dental applications as: (a) temporary,

intermediate and, in some cases, more permanent restoratives; (b)

cavity liners and bases, (c) luting agents to bond preformed

restorations and orthodontic devices, (d) pulp capping agents and

endodontic sealers and (e) impression pastes. This wide range of

dental uses makes it virtually impossible for one type of cement to

have all the necessary properties^ demanded in these diverse

applications. Therefore, there is a need to develop "tailored"

dental cements with a view toward maximizing the properties needed

to fulfil their ultimate functions. One approach for improving the

overall properties of dental cements involves developing hybrid

cement-composites or resin-modified cements.

Objective

To enhance the durability of dental cements by improving their

hydrolytic stability, especially under acidic oral conditions

(e.g., in plaque coated areas), and by moderating their brittle

nature while increasing their tensile and flexural strengths.

Introduction

A novel, versatile class of dental cements, non-aqueous

polycarboxylate cements (termed haltopolymers) , were developed from

the commercially available C36 and C 34 hydrocarbon polycarboxylxc

acids, designated dimer (DA) and trimer (TA) acids. The divalent

metallic dimerates and trimerates matrices of these cements are haltopolymers, a term coined to denote their dual salt-like and

polymer-like character. All of these cements have water repellent

properties due to their chain structures consisting of large

paraffin segments linked by a few hydrophilic carboxylate groups.

Some of these cements, especially those derived from calcium bases,

display energy-absorbing qualities under compressive stress. These

cements do not inhibit the polymerization of resin based dental

materials (as do engenol based cements) and, in fact, can be

formulated to yield strong hybrid composite cements. The calcium

hydroxide based cements have low solubilities and enhanced

hydrolytic stability but still provide an alkaline environment

which may promote secondary dentin formation, and thus have

potential utility as cavity liners, endodontic sealers, etc.

Further details on the properties of these cements are contained in

the abstracts and microfilmed papers presented at IADR meetings in

1984 and 1985 and at the 10th Annual Meeting of the Society for

Biomaterials in Washington, DC, 1984 [48-50]. An invited talk on

the properties of hydrophobic, energy absorbing dimer acid cements

was given at the Dental Materials Conference at St. Andrew's

Scotland, UK, in 1985.

34
Glass ionomers are relatively high modulus cements which adhere to

enamel and, to a lesser extent, to dentin. With minimal surface

preparation, adhesive strength is higher to enamel than dentin

(presumably because of the lower mineral content of the latter) but

is relatively low in either case because of the low tensile

strength inherent in this type of material. Glass ionomer cements

also display a susceptibility to excessive hydration during the

early stages of their setting reaction which results in an inferior

cement. In addition, the hardened cement has a propensity to

dehydration, brittle fracture and erosion under acidic conditions.

PROGRESS REPORT

Phase I

(a) A DA cement formulated with 1 part Ca(0H)2 and 1 part

Ca3 (P04 ) 2 in a powder-liquid ratio of 2 displayed a positive

volume change on setting (24 h)of 2.04% + 0.94%.

(b) Resin-modified dimer acid cements . Since dimer acid (DA)

cements do not inhibit the free radical polymerisation of

vinyl monomers, resin-modified DA cements or hybrid cementcomposites (HCC) with acceptable setting times (3-8m) can be

formulated into high tensile strength materials that may have

utility as intermediate restoratives, bases, liners, etc.

Strong HCC's can be formulated containing various amounts of

Ca(0H)2 which may have potential as promotors of reparative

dentin. HCC's can be formulated as paste/paste or powder/liquid chemically activated systems. Photochemically

activated, single paste formulations also can be prepared.

In table 3 are shown the formulation of two powder/liquid

(P/L) HCC's with their 24h diametral tensile (DTS) and

compressive strengths (CS) . The glass used in these

formulations was a conventional radiopaque glass (45um)

silanized with 0.5% by weight of 3-

methacryloxypropyltrimethoxysilane (A-174) and coated with 1%

by weight of benzoyl peroxide. The DTS values represent a four-to fivefold increase over the unmodified DA/Ca(0H)2

cement. CS values of HCC's also are significantly higher.

35
Table 3

Formulation

I

II

DA

EBPDMA

HMDMA

DHEPT

DMAPE

BP

24 B Mechanical Properties of Resin Modified (DA/Ca(0H)2 Cement

Components in Components in

Liauid/w% Powder/wt% P/L DTS ( STD DEV) CS (STD DEV)

DA 27.0 Ca (OH )

2

25.0 2.5 21.2 (1.4) 56.7 (5.4)

EBPDMA 42.7

HMDMA 30.0 Silanized 75.0

DHEPT 0.3 Glass (1%BP)

DA 33.0 2.5 21.5 (0.6) 68.4 (6.4)

BIS-GMA 48.1

HMDMA 18.7 Same as in I DMAPE 0.2

= Dimer Acid

= Exthoylated bisphenolA dimethacrylate

= 1.6 hexamethylene dimethacrylate

= N , N-bis ( 2-hydroxyethyl ) p-toluidine

= P-N,N-dimethylaminophenethanol

= Benzoyl peroxide

(a) Resin-Modified Glass Ionomer Cements (New) . An approach

towards ameliorating the aforementioned deficiencies of the

glass ionomer cement is to incorporate into the formulation a water soluble or compatible vinyl resin capable of

interpenetrating or blending with the cement during a dual

cure process. Ideally an interpenetrating polymer network

(1PN) develops by combining the ionic setting reaction of the

glass ionomer with the vinyl addition polymerization of a compatible resin as shown in Fig. 6. The resulting resinmodified cement or hybrid cement-composite (HCC) is expected

to have a "rubber toughened" and less permeable nature which

should deter catastrophic failure and increase resistance to

acidic penetrants. The tendency to undergo

hydration/dehydration also should lessen.

Using a water hardening glass ionomer cement (Chemfil II) , 2-

hydroxyethyl methacrylate (HEMA) , ascorbic acid (AA)

,

hydrogen peroxide (HOOH) and a trace of a water soluble

cupric salt (CuSO^ 5 H2 O) , a hybrid cement-composite (HCC) was formulated (Table 4). AA and CuS04 . 5 H2 O were blended with

the Chemfil II powder (a blend of powdered polyacid and ionleachable calcium aluminum f luorosilicate) . HEMA, an aqueous

solution of HOOH, and a silane coupling agent (A-174) were added to distilled water to provide the liquid component of

the HCC which contains about 30% less water than the

unmodified Chemfil II cement.

36
Table 4

Compositon of Hybrid Cement Composite (HCC)

Composition of Weight Composition Weight

Powder Percent of Liquid Percent

Chemfill II powder* 99.28 HEMA 28.40

A-174 0.60

Ascorbic Acid 0.70 HOOH 1.30

CuS04 5HzO 0.02 H2 0 69.70

Maximum Powder/Liquid Ratio (wt/wt) -6 - 6.7

Detrey/Dentsply

On mixing the components, a workable paste results which

appears less subject to hydration during setting than the

unmodified glass ionomer. In addition, a significant

improvement in diametrial tensile strength occurs along with

a modest decrease in compressive strength (Table 5) . The

working and setting times of the HCC cement are somewhat

longer than those of the unmodified cement but still

clinically acceptable (working time about 2 m, set time about

4 m from start of mix at 23 °C)

.

Table 5

24 Hour Diametral Tensile (DTS) and Compressive Strengths (CS) of HCC

Powder/Liquid Ratio DTS, MPa , (STD DEV) CS, MPa, (STD DEV)

HCC 6.7 25..1 (2.1) 138.9 (5.9)

HCC 6.0 24..3 (3.5) 130.3 (6.7)

Chemfil II 6.0 16,.7 (1.9) 143.4 (10.1)

Other properties (transverse strength, adhesive

strength, microleakage, etc.) of this type of HCC are being evaluated.

Phase I. Tasks (3) and (4) are deferred until later.

III. Development of Improved Interfacial Bonding Systems and Fillers for

Composites and Cements

Overview (Filler)

On a weight basis the major component of dental composites is

usually the reinforcing filler (e.g., 50-86%). For many properties

of the composite the volume percent of the dispersed phase is a more significant parameter. The reinforcing filler performs many

37
functions in a composite such as stiffening the lower modulus resin

binder thereby increasing mechanical properties, enhancing

dimensional stability, moderating the exotherm of polymerization

and the mismatch between the thermal expansion of the organic

matrix and tooth structure, reducing water sorption and

polymerization shrinkage, and aiding in matching tooth appearance.

By using glass or ceramic fillers that have refractive indices

approximately those of the matrix they can be used to form

translucent fillings that match the translucency of tooth

structure. The selective inclusion of compounds with elements of

high atomic number (e.g., barium, strontium, lanthanum, zinc,

zirconium, titanium, etc.) in the preparation of glass fillers

yields esthetic composites with a degree of radiopacity.

A variety of types, shapes and sizes of fillers have been used in

dental composites, e.g., quartz, fused silica, borosilicate and

aluminosilicate glasses, silicon nitride, calcium silicate, calcium

phosphates, aluminum oxide, metals, etc. In addition, submicrcn

fillers such as precipitated or pyrogenic silicas (0.14-0.007 0 m)

averaging 0.04 0 m in size have been used in microfilled composites.

The high surface area of this type of filler makes it difficult to

achieve high filler loadings by weight in this type of composite,

e.g., 50 weight percent is usually the maximum. To enhance their

miscibility and dispersion in resin systems, small organic-rich,

composite macrofillers are made from pulverized, prepolymerized

composites derived from the silanized, microfine fillers and the same or similar monomer systems. Composites formulated with these

prepolymerized composite fillers also are termed microfilled

composites

.

Compared to conventional composites with their larger filler sizes

(0.7 to 100 0 m, but usually 3-5O0m) , microfilled composites have a smoother, more easily polishable surface texture which may reduce

the adherence of plaque and stains. On the other hand, they have

lower moduli and tensile strength, exhibit more creep and have

higher water uptake, thermal expansion and polymerization shrinkage

than conventional or hybrid composites.

Hybrid composites, which incorporate major quantities of the

smaller sized macrofillers along with small amounts of

microfillers, achieve almost as smooth a surface texture as the

microfilled composites without compromising (often actually

improving) other properties. Some of the newer hybrid composites

have a multimodal dispersed phase consisting of different types,

shapes and sizes of fillers.

An innovative approach to enhance the interfacial bonding of the

inorganic and organic phases of the composite is through the use of

"semiporous" glass fillers obtained by selectively acid etching the more soluble phase of glass particles having two interconnected

vitreous phases [52,53]. Properly done this results in a glass

filler having superficial surface porosity into which the resin can

38
flow and mechanically interlock on polymerization, thus

complementing the usual bonding through silane coupling agents

.

The search for dental composites of superior wear resistance for use in stress-bearing applications has spurred research into new

types of stable fillers of sizes and shapes conductive to optimal

packing efficiency. New techniques to significantly increase

filler loadings have appeared in [54,55].

Overview (Intarfacial Bonding Systems)

Although it is only a minor component of resin based dental

restorative materials, an interfacial bonding agent exerts a profound effect on the durability of composites. The quality of

the interfacial bonding phase existing between the polymeric matrix

and the dispersed phase exerts a significant effect on the ultimate

properties and the clinical performance of dental composites. Even

composites prepared from the best of resin binders and reinforcing

fillers will be deficient in durability if water and other

contaminants penetrate and disrupt the interfacial bonding phase.

Bifunctional coupling agents such as organof unctional silanes,

titanates, zirconates, etc., are used in composites to promote

adhesion between mineral fillers and organic resin binders.

Alkoxysilanes having terminal vinyl groups have been the most

widely used type of coupling agent for dental composites.

Initially, a vinyltrialkoxysilane was used but it was later found

that 3-methacryloxypropyltrimethoxysilane was more effective.

Alkosysilanes can react with surface moisture, usually present at

least as a monolayer on mineral surfaces, to generate silanol

groups which can strongly hydrogen bond to hydroxylated surfaces.

In addition, silanol groups can react chemically with surface

hydroxyl groups of the filler via covalent bond formation. There

is some direct (e.g., spectroscopic) evidence that suggests that

these kinds of reactions do occur between silane coupling agents

and many types of mineral fillers used to reinforce composites.

Organof unctional silanes can be visualized as reacting by both

hydrogen bonding and/or covalent attachment to mineral fillers by

virtue of their silanol or derivative groups and by

copolymerization with the resin system via their terminal vinyl

groups. Indirect evidence for this interfacial bonding is provided

by the observed enhancement in mechanical strength and resistance

to water and other chemicals of silanized composites.

The effectiveness of coupling agents in a composite depends on a number of factors: (1) the nature of the resin binder and filler,

(2) the structure and chemical reactivity of the coupling agent (3)

the amount used and (4) the mode of application.

39
Objective

To develop filler and interfacial bonding systems of enhanced

durability applicable to dental composites and cements (filler

portion of project is new)

.

PROGRESS REPORT

Phase I. Development of Improved Interfacial Bonding Phases for

Composites and Cements.

The objective of the first part of this study was to evaluate

various types of silane agents and silanization techniques

for their efficacy in dental composites.

Commercial silane agents evaluated included:

3-methacryloxypropyltrimethoxysilane (MAPS)

,

3-methacryloxypropyldimethylethoxysilane (MAPES)

3-methacryloxypropyldimethylchlorosilane (MAPCS)

,

3-mercaptopropyltrimethoxysilane (MPS)

,

3 ,N,N-dimethylaminopropyltrimethoxysilane (DMAPS)

3-N,N-dimethylaminophenyltriethoxysilane (DMAIS)

and experimental multifunctional silane agent, BISGMA/(IPTES )2 (see Fig. 7) which was synthesized for this

study.

The results of this phase of this study indicate that

methacryl based silanes performed best as interfacial bonding

agents (assessed by diametral tensile strength and transverse

strength measurements) . MAPS yielded composites with the

highest strength values; MPS had some modest coupling action

compared to the control (composite with unsilanized glass)

.

DMAPS, in addition to being a poor silane agent, is also a poor photoreductent for camphorquinone (CQ) . DMAIS, although

a highly effective photoreductant for CQ, did not show any

appreciable interfacial bonding qualities. The experimental

silane agent, BIS-GMA/ (IPTES )

2

yielded composites that had

the most hydrolytically resistant interfacial bond as determined from DTS and TS measurements after 7 days thermal

cycling (5 °C - 55 °C) experiments. TS measurements are more sensitive than DTS determinations in assessing the quality of

the interactial bond.

Silanization techniques explored included (a) integral

blending, (b) presilanization at different temperatures (80°,

110°, 140°C) and (c) dual silanization. Integral blending

yielded composites with about the same diametral tensile

strengths as presilanized derived composites. However, as measured by transverse strength techniques and after thermal

cycling, presilanized composites gave higher TS and better

retention of other mechanical properties. The use of a dual

silanization technique combining presilanization and integral

40
blending shows promise of yielding more durable composites

.

A more detailed description of this study was presented at

the 1986 AADR meeting.

Phase II. To develop improved, more durable interfacial bonding

systems and fillers for composites and cements. (Filler portion of

project is new.)

In addition to our silanization studies using a conventional

radiopaque glass, a preliminary silanization study of a softer, nonsiliceous filler was explored. Sodium calcium

metaphosphate, NaCa(PC>3)3, is a commercially available

fibrous filler that is being used in a variety of composite

applications. Composites were prepared using this filler as received and after treatment with a silane agent. Mo

significant differences were noted in the diametral tensile

strengths or transverse strength of the silanized and

unsilanized specimens.

A potential non-silane coupling agent also was evaluated for

calcium phosphate fillers. PMBM (the diadduct of HEMA and

pyromelletic anhydride) was evaluated as a coupling agent for

resin based calcium phosphates and metaphosphates composites.

Preliminary results indicate that under the conditions used

to apply PMDM to the mineral (room temperature, acetone) no significant coupling occurs between the methacrylate resin

and tricalcium phosphate or calcium metaphosphate. Both

chemical and visible light cured composites were used in the

study.

IV. Bonding of Low Surface Energy Resin Systems to Tooth Structure (New

Project)

Objective

To develop durable bonding systems for tooth structure compatible

with a variety of resin based dental materials especially those of

low surface energy.

Overview

Currently used resin based dental composites are not adhesive to

tooth structure. However, the discovery of the acid etch technique

made it possible to bond resin based dental materials to enamel by

a micromechanica) interlocking mechanism [5,6]. Surface

microporositv is generated on enamel by a brief pretreatment with

aqueous phosphoric acid or certain types of organic acids e.g.,

pyruvic, citric, etc. The usual acid etch technique is probably

generally ineffective and contraindicated for use with dentin.

Adhesion to dentin has presented a more challenging problem. On a weight basis dentin consists of 69% hydroxyapatite, 13% organic

41
matter (mainly collagen) and about 13% water. An adhesive bonding

or coupling agent for this substrate would mean less invasive

cavity preparations with decreased loss of sound tooth structure

and a reduction in microleakage with its potential for secondary

caries formation. Considerable effort has been devoted to the

development of coupling agents that can mediate bonding between

dental resins and apatitic substrates [7-16]

.

Surface-active comonomers that can bond to apatitic substrates by

chelation of surface Ca+Z and/or other multivalent cations have

been made by the reaction of N-substituted aryl glycines (for

example, NPG, NTG) with glycidyl methacrylate (GMA) . Other types

of coupling agents are functional vinyl monomers that have groups

capable of reacting with collagen by specific chemical reactions,

e.g., esterification, urethane or schiff base formation. Another

approach for chemically bonding to collagenous substrates involves

graft polymerization techniques using free radical initiation [7-

16] .

Recently three types of adhesion-promoting systems have

demonstrated rather strong adhesion to dentin. One system involves

pretreatment of dentin with an aqueous solution of 2-hydroxyethyl

methacrylate (HEMA) and glutaraldehyde [13,14]. The critical

component of the second bonding system is the functional monomer 4-

methacryloxyethyl trimellitic anhydride, 4-META [9,10]. The third

bonding procedure utilizes a brief application of a cleanser,

mordant aqueous solution of ferric or aluminum oxalate, a surface

active comonomer such as MPG-GMA or NTG-GMA and PMDM, the diadduct

of HEMA and pyromellitic anhydride [8,15,16]. The latter two

bonding systems display significant adhesion to enamel as well as dentin.

PROGRESS REPORT

Phase I. In collaboration with Dr. Rafael Bowen of the American

Dental Association Health Foundation, Paffenbarger Research Center

(APAHFPRC) we are synthesizing a series of carboxylated monomers,

one of which should act in a manner analogous to PMDM and 4-META

[8-10,15]. These coupling agents should exhibit improved

compatibility with dentin because they have amide groups in their

structure as well as carboxyl groups (CO2 H)

.

A surface-active monomer analogous to PMDM, was prepared from

3 ,

3

1 ,4,41 -benzophenonetetracarboxylic diahydride (BTDA) and

t-butylaminoerhyl methacrylate (TBAEM) . The reaction was carried out in methylene chloride by adding dropwise a solution of TBAEM in this solvent to a stirred solution of

BTDA at room temperature. Two moles of TBAEM were used to one of BTDA to yield after removal of the solvent the

diadduct as a viscous yellow liquid. Purification by

trituration with cyclohexane yields a purer product which

slowly solidifies on standing. This monomer is polymerizable

42
by exposure to UV irradiation. XR analysis supports the

structure of this coupling agent as having difunctional

amidoethyl methacrylate with free COzH groups. The

benzophenone unit in the structure confers on this monomer photoactivity

.

Phase IX. A third type of bonding agent based on some of our early

work and that of Asmussen will be synthesized from 2-hydroxyhexanedial and methacryloxyl chloride and evaluated as an adhesion

promoting comonomer for dentin later in the project [11,13,14].

Research on the synthesis of fluorinated coupling agents also has

been deferred pending availability of starting materials. A new project utilizing the potential bonding capabilities of the newly

developed resin modified glass ionomer cements or hybrid cementcomposites (HCC) has been initiated in collaboration with members

of ADAHPRC.

43
References

[1] Bowen, R.L. Use of epoxy resins in restorative materials. J. Dent. Res.

35 360 (1956)

.

[2] Bowen, R.L. Dental filling materials comprising vinyl silane treated

fused silica and a binder consisting of the reaction products of

bisphenol and glycidyl methacrylate, U.S. Patent 3,066,012 (1962).

[3] Wilson, A.D. The chemistry of dental cements. Chem. Soc. Rev. 7 265

(1978).

[4] Wilson, A.D., Prosser, H.J., and Fowls, D.R. Mechanism of adhesion of

polyelectrolyte cements to hydroyapatite. J. Dent. Res. 62 590 (1983).

[5] Buonocore, M.G. Simple method of increasing the adhesion of acrylic

filling materials to enamel surfaces. J. Dent. Res. 34 849 (1965).

[6] Silverstone, L.M. The structure and characteristics of human dental

enamel in biocompatibility of dental materials. Vol. 1, Smith, D.C. and

Williams, D.F., eds. (RC Press Inc.) Boca Raton, FL, Chap. 2 (1982).

[7] Brauer, G.M. Adhesion and adhesives in scientific aspects of dental

materials. Von Fraunhofer, J.A., ed. Butterworths , London, Cap. 2 (1975).

[8] Bowen, R.L., Cobb, E.N. and Rapson, J.E. Adhesive bonding of various

materials to hard tooth tissues. Improvement in bond strengths to

dentin, J. Dent. Res. 61 1070 (1982).

[9] Yamauchi, J., Nakabayashi, N. and Masuhara, E. Adhesive agents for hard

tissue containing phosphoric acid monomers, ACS Polym Prepr. 20 594

(1979).

[10] Atsuta, M., Abell, A.K., Turner, D.T., Nakabayashi, N. and Takeyama, M. A new coupling agent for composite materials: 4-methacryloxyethyl

trimellitic annhydride, J. Biomed. Mater. Res. 16 619 (1982).

[11] Antonucci, J.M. Aldehyde methacrylates derived f romhydroxybenzaldehydes

.

J. Dent. Res. 57 500 (1978)

.

[12] Antonucci, J.M., Brauer, G.M. and Termini, D.J. Isocyanate urethane

methacrylates derived from hydroxyethyl methacrylate. J. Dent. Res. 59

35 (1980).

[13] Asmussen, E. and Munksgaard, E.C. Bonding of restorative resins to

dentin by means of methacryloyl chloride and methacryloyl-R-isocyanate

,

Scand. J. Dent. Res. 91 153 (1983).

[14] Asmussen, E. and Munksgaard, E.C. Bonding strengths between dentin and

restorative resins mediated by mixtures of HEMA and glutaraldehyde. J. Dent. Res. 63 1087 (1984)

.

44
[15] Bowen, R.L. and Cobb, E.N. A method of bonding to dentin and enamel.

JADA 107 734 (1983)

.

[16] Bowen, R.L., Cobb, E.N. and Misra, D.N. Adhseive bonding by surface

initiation of polymerization. Ind. Eng. Chem. Prod. Res. Dev. 23 78

(1984)

.

[17] Wu, W. , and McKinney, J.E. Influence of chemical on wear of dental

composites. J. Dent. Res. 61 1180 (1982).

[18] Wu, W. and Debelius, E.E. Environmental resistance of dental restorative

materials. J. Dent. Res. 6_3 199, Abstr. 255 (1984).

[19] Wu, W., Toth, E.E., Moffa, J.F. and Ellison, J.A. Subsurfasce damage of

in vivo worn dental composite restorations. J. Dent. Res. 6_3 675 (1984).

[20] Soderholm, K.J. Degradation of glass filler in experimental composites.

J. Dent. Res. 60 1867 (1981)

.

[21] Ibid. Leaking of fillers in dental composites. J. Dent. Res. 62 126

(1983) .

[22] Ibid. Hydrolytic degradation of dental composites. J. Dent. Res. 62

1248 (1984) .

[23] McKinney, J.E. Influence of acids on wear of composite restoratives. J. Dent. Res. 62 199 Abstr 256 (1984).

[24] Antonucci, J.M., Venz, S., Stansbury, J.W. and Dudderar, D.J. Low

surface energy dental composites from a polyf luorinated prepolymer

multifunctional methacrylate. Proceedings of the 1st Medical Plastic

Conference of the Society of the Plastics Industry, Inc., New Brunswick,

NJ (1983).

[25] Kuo, J.S., Antonucci, J.M. and Wu, W. Evaluation of siloxane-containing

dental composites. J. Dent. Res. 64 178, Abst. 30 (1985).

[26] McKinney, J.E. and Wu, W. Effect of cure on hardness and wear of three

commercial dental composites. J. Dent. Res. 62 285, Abst. 1047 (1983).

[27] Antonucci, J.M., Stansbury, J.W., and Dudderar, D.J. Dental resin and

initiator systems based on polythiols. J. Dent. Res. 61. 270, Abst. 824

(1982) .

[28] Venz, S. and Antonucci, J.M. Effect of a polythiol on the degree of

polymerization of resins. J. Dent. Res. 62 199, Abst. 257 (1984).

[29] de Rijk, W.G., Conner, M.L. Jennings, K.A. and Wu. W. The in vivo wear resistance of dental composites with enhanced polymerization. J. Dent.

Res. 63 286, Abst. 951 (1983)

.

[30] Antonucci, J.M. New monomers for use in dentistry. Biomed. and Dental

45
Applications of Polymers, eds., Gebelein, C.G. and Koblitz, F.F. Plenum

Press, NY, NY, 357-371 (1981).

[31] Antonucci, J.M., Stansbury, J.W., and Venz, S. Synthesis of a polyf luorinated prepolymer multifunctional urethane methacrylate. J. Dent. Res. 64 209, Abst. 308 (1985).

[32] Venz, S. and Anatonucci, J.M. Degree of cure and polymerization

shrinkage of photoactivated resin based materials. J. Dent. Res. 64 229,

Abst. 488 (1985) .

[33] Ruyter, I.E. and Gyorosi, P.P. An infrared spectroscopic study of

sealants. Scand. J. Dent. Res. 84 (1976).

[34] Ruyter, I.E. and Swendsen, S.A. Remaining methacrylate groups in

composite restorative materials. Acta, Odontol Scand 36. 75 (1978).

[35] Ferracane, J.L. and Greener, E.fl. Fourier transform infrared analysis of

degree of polymerization in unfilled resins: methods comparison. J. Dent. Res. 63. 1093 (1984) .

[36] Asmussen, E. Restorative resins: hardness and strength vs quantity of

remaining double bonds. Scand. J. Dent. Res. 90 484-489 (1982).

[37] Lutz, F., Phillips, R.W., Roulet, J.F. and Setcos, J.C. In vivo an in

vitro wear of potential posterior composites. J. Dent. Res. 6^ 914

(1984).

[38] Smith, D.C. A new dental cement. Br. Dent. J. 125 381 (1968).

[39] Wilson, A.D. and Kent, B.E. A new translucent cement for dentistry. The

glass-ionomer cement. Br. Dent. J. 132 133 (1972).

[40] Wilson, A.D. and Prosser, H.J. Aluminosilicate dental cements. Ref. 6,

Chap. 3, Vol . 3 (1982) .

[41] Wilson, A.D. and Prosser, H.J. Br. Dent. J. 157 449 (1984).

[42] McLean, J.W. Alternatives to amalgram alloys, Br. Dent. J. 157 432

(1984).

[43] Sakaguchi, R., Delong, R. and Douglas, W.H. Friction and wear of

posterior enamel in an artifical mouth. J. Dent. Res. 64 370, Abst. 1763

(1985) .

[44] Douglas, W.H., Delong, R., and Sakaguchi, R. Surface frictional changes

in posterior materials during wear experiments in an artifical mouth. J. Dent. Res. 64 370, Abst. 1764 (1985).

46
[45] Delong, R., Sakuguchi, R. and Douglas, W.H. Occlusal wear of posterior

materials in an artificial mouth. J. Dent. Res. 64 371, Abst. 1765

(1985).

[46] Anzai, M. and Ohashi, M. Studies on the reaction product of

hexachlorocyclotriphosphazene and 2~hydroxyethyl methacrylate and on the

physical properties of the polymer, J. Nihon Sch. Dent. 26 109 (1984).

[47] Ibid. Studies on composite resins with hexa (methacryloyl-ethylenedioxy)

cyclotriphosphazene used as a monmer. J. Nihon Sch. Dent. 26 238 (1984)

[48] Antonucci, J.M., Venz, S., Dudderar, D.J., Pham, M.C. and Stansbury, J.W

Non-aqueous polycarboxyate cements based on dimer and trirner acids. J. Dent. Res. 63 294, Abst. 394 (1984).

[49] Antonucci, J.M., Venz, S., Dudderar, D.J., Pham, M.C. and Stansbury, J.W

Energy-absorbing, hydrophobic dental cements based on dimer and trimer

acids. Second World Congress on Biomat., 10th Anual Meeting of the

Society of Biomat., Transactions, VII, 137 (1984).

[50] Dudderar, D.J. Esthetic, non-brittle dental cements based on dimer acid

J. Dent. Res. 64 163, Abst. H6 (1985).

[51] Barton, J.A., Brauer, G.M., Antonucci, J.M. and Ramey, M.J. Reinforced

polycarboxylate cements. J. Dent. Res. 5_4 310 (1975) .

[52] Bowen, R.L. and Reed, L.E. Semiporous reinforcing fillers for composite

resins. I Preparation and provisional glass formulation. J. Dent. Res

55 738 (1976) .

[53] Bowen, R.L. and Reed, L.E. Semiporous reinforcing fillers for composite

resins. II. Heat treatments and etching characteristics, ibid 748

(1976) .

[54] Cross, M., Douglas, W.H. and Fields, R.P. The relationship between

filler loading and particle size distribution in composite resin

technology. J. Dent. Res. 62^ 850 (1983).

[55] Nemcek, J., Roberts, T.A., and Sherliker, F.R. U.S. Patent 4,374,937

(1983) .

Patents

Davis, G.T., Chiang, C.K., Antonucci, J.M. and Takahashi, T. Polyethylene

inine-metal soft solid polyelectrolyte. U.S. Patent 4,576,382 (1986)

Antonucci, J.M. Dental composite formulation from acrylate monomer and

polythiol accelerator. U.S. Patent 4,536,523 (1985).

47
Publications

Brauer, G.M. and Antonucci, J.M. Dental applications (of polymers)

.

Encyclopedia of Polymer Science and Engineering, Vol. V, 2nd ed. WileyInterscience , NY, NY 698-719 (1986)

.

Manuscripts Accepted for Publication

Antonucci, J.M. Resin based dental composites - an overview. Proceedings of

the 2nd International Conf. on Polymers in Medicine, Biomed. and Pharmaceutical

Applications, Capri, Italy (in press)

.

Manuscripts Approved by WERB

McKinney, J.E., Antonucci, J.M., and Rupp N.W. Wear and microhardness of a metal-filled glass-ionomer cement.

Kuo, J.S., Antonucci, J.M. and Wu, W. Evaluation of sioxane-containing dental

composites

.

Dudderar, D.J. and Antonucci, J.M. Esthetic, non-bnttle dental cements based

on dimer acid.

Manuscripts Under Review by WERB

Antonucci, J.M.', Stansbury, J.W., Dudderar, D.J. and Venz, S. Dental resin and

initiator systems based on polythiols.

Venz, S. and Antonucci, J.M. Effect of a polythiol on the degree of

polymerization of resins.

Antonucci, J.M., Dudderar, D.J., Stansbury, J.W. and Venz, S. Non-aqueous

polycarboxylate cements based on dimer and trimer acids.

Venz, S., Rupp, N.W. and Antonucci, J.W. Microleakage and water sorption of

hydrophilic and hydrophobic dental composites.

Antonucci, J.M., Stansbury, J.W. and Venz, S. Synthesis of a polyf luorinated

prepolymer multifunctional uraethane methacrylate.

Invited Talks

Antonucci, J.M. Composites for dental applications, University of Connecticut,

Institute of Material Science, Storrs, CT, (Oct. 1985).

Antonucci, J.M. New trends in dental composites, Dentsply Inti., York, PA

(July 1986) .

Antonucci, J.M. Discussion Leader for Gordon Conference on Adhesion, New

Hampton, NH (Aug. 1986) .

48
Contributed Talks

McKinney, J.E., Antonucei, J.M. and Rupp, N.W. Wear and microhardness of a metal-filled ionomer cement. J. Dent. Res. 65 344, Abstr. 1577 (1986).

McKinney, J.E. and Antonucei, J.M. Wear and microhardness of two experimental

dental composites. J. Dent. Res. 6_5 848, Abstr. 1101 (1986).

Antonucei, J.M., Stansbury, J.W. and Venz, S. Synthesis of silyl ether

derivatives of BXS-GMA. J. Dent. Res. 65_ 219, Abst. 451 (1986).

Venz, S. and Antonucei, J.M. Silanization and modification of fillers for

dental composites. J. Dent. Res. 65 191, Abst. 191 (1986).

49
Figure 1

CF, CFS

I CF,

C-OCH 2-CH-CH;OC»CH=CH-CH2-C-OCH:-CH-CH2“0 —

I CF

I

' ?

. CO

INH

i CH,

I 2 CH,

i z 0

1 c=o

I CH,=C 2

1 CH,

l CF3 cf3

PFUMA

« 0

8 CO

1NH

CH,

i 2 CH,

i i O

s

i c=

ICH

CH,

MW = 1 2 ,060

%F = 37.8

O CH,

i! ; CH 2 =C — C-OCH, — CH,— CH, — SiI I CH 3 CH 3

(3IS-HPTMS)

Structural formulas for (a) PFUMA and (b) 3IS-MPTMS

50
U4

Figure 2

ii CH, = C — C-0-(-

ini

o

II oc-c=.ch, k

.

DM DMA

1, 10-Dccamethylene no/ Dimethacrylate

310

CH

2

PFrlA CH

2

MW of Repeating Unit - 1032

MW = 10,320 Percent F = 44.2

51
Figure 3

SYNTHESIS OF BIS(METHACRYLOXYPROPYLDIMETHYLSILYL)

ETHER OF BIS-CMA

CH. L

-q-ch

2

-ch-ch

2 «q»c-och

2

QH CH.

* B I S - G M A

SOLVED

CH CH

H C-C-C"0“CH CH CH -Si-X

2 ii 2 2 2

CH

Q

H C=C-C-ChCH_-CH-CH? -0-

2

! 2

! 2

G-L Q

0

-O-CH.-CH-CH -Q-C-OCH

2

i

i Q CH.

CH^-Si-CH^

CH

0

I 0-C

•CH.

SIS-GMA/ (MAPDMS)

,

mw - aao

X * Cl, OCH

2CH

2

, etc.

CH -Si-CH

3

I 3 CH

2

CH

CH

2

0

I oc

!r.-CH

3

CH.
F 1 gur e 4

SYNTHESIS OF OLIGOMERIC SILYL ETHERS OF BXS-GMA

METHOD A

CH Cl

2 2

Et M

3

CH

3 C1S1—R

ICH

3

53
Figure 5 SYNTHESIS OF OLIGOMERIC SILYL ETHERS OF 8 IS-GMA

METHOD B

m-c

6 h

1

4

/ch,cl

2

CH

3

CH CH CH

! 3

1 3 / 3 SI — R — 31 —

N

CH

1 CH1 \CH

3 3 3
Figure 6

CaAlFSIO HO

3 _—.2

y

,

POLKACID ION' hE*i!*

BLE

BLENDED POWDER

C*,A1 Pelyealt

Hydregei

* CaAlFSIO^

(excess,

partial ly L reacted?

"IONOMER CEMENT®

nCH

2

CH

li.

HOOH AA

CH

CH

OH

HEMA

HEHA - 2-HYDROXYETHYL METHACRYLATE

AA - ASCORBIC ACID HOOH - HYDROGEN PEROXIDE

2 Cu - SOLUBLE CUPRIC SALT

CH*

CH

i 3 C —

0

S CH

I 2 CH

I 2 OH

POLY (HEHA)

HEHA/H 0 Ca.Al POLYSALT

•* CaAlFSIO

c w HYDROGEL

3 HOOH

> CaAlFSIO

2 (AA Cu ) 3 POLY (HEMA)

v , MODIFIED BLENDED POWDER

"HYBRID CEMENTCOMPOSITE"

AA - ASCORBIC ACID HOOH - HYDROGEN PEROXIDE

2Cu - SOLUBLE CUPRIC SALT

(c)

Polymerization mechanisms for (a) conventional water hardenable

glass ionomer cement, (b) aqueous free radical polymerization of

water soluble monomer, and (c) hybrid cement composite (HCC).

55
Figure 7

SYNTHESIS OF A MULTIFUNCTIONAL SILANE AGENT

(DIADDUCT OF BIS-GMA AND 3~ISOCYANATQPROPYLTRIETHOXYSILANE)

2 « 2 i 2

CH

3

L

o

"Q-CH_-CH-CH_“0“C-C=CH

2

| 2

| 2

OH CH.

BIS-GMA

CH

2

C1

2 OCNCH CH CH Si/OCH CH

2 2 2 1 2 3

'

IPTES

CM.

|| h (>c-c-o-ch2

-c;h-c^

2

“Q--

i

i NH

! CH

f* —c—

tCH,

BIS-GMA/ (i PTES

)

MW - 1006 2

0

-o-ch

2

-ch-ch

2

-o-c-c=ch.

ch.

C-0

! HN

ICH

CH CH

CH CH

CH -CH -O-Si-O-CH -CH

3 2 , 23

0

iCH

CH -CH -Q-SI-O-CH -CH

3 2, 23

0

! CH

CH CH

56
II WEAR RESISTANCE AND DURABILITY ASSESSMENT OF DENTAL COMPOSITE RESTORATIVE

MATERIALS

Overview

This part of the annual report includes descriptions and results of

experimental procedures used by the NBS Dental and Medical Materials Group to

evaluate the performance of dental composite restorative materials . The

methods employ both in vivo and in vitro wear testing, microhardness,

viscoelastic measurements, and raicrodefect analyses. The objectives are to use appropriate techniques to define and delineate fundamental wear mechanisms

applicable to the in vivo wear of these materials. The results from these

studies are expected to facilitate the development of improved prototype

composite restoratives here and at other laboratories.

This task is divided into the following sections:

A. Wear and Durability Assessments of Composite Restoratives

Phase I. Recent commercial composites which appear promising for

posterior occlusal application.

Phase II. Experimental composites with flexible polymers.

Phase III. Glass-ionomer cements: conventional, metal-filled, and

modified experimental.

Phase IV. Susceptibility of commercial dental composites to

topical fluoride gels (new task)

.

Phase V. Experimental studies on experimental composites employing

apatite fillers (not active this period)

.

B. Glass-Transition Temperature (Tg ) of Matrix Polymers

C. Wear Instrumentation (new task).

Phase I. Methodology for improved wear apparatus.

D. Clinical Examinations Employing Removable Partial Dentures

A. Wear and Durability Assessments of Composite Restoratives

Background

Clinical data and microdefect analyses on in vivo worn restoration

biopsies revealed that both mechanical wear and the intraoral environment

play an important role in the degradation of composite restorations. For

this reason we believe that a relevant wear test should, in some way,

include the influence of the intraoral environment. Accordingly, the wear test specimens were preconditioned in appropriate liquids prior to

testing. Since dental composites comprise two major components, polymer

57
matrix and inorganic reinforcing filler, appropriate fluids were selected

to evaluate the corresponding degradation mechanisms separately.

Our earlier work involved microhardness and wear tests, along with

certain other tests, on commercial composite specimens in order to

delineate their degradation mechanisms. In order to study potential

problems with the matrix, the composite specimens were preconditioned

(for usually one week) in selected organic solvents for which the

solubility parameter was varied over the range applicable to liquid-food

ingredients. When the solubility parameter of the solvent approximated

that of the matrix resin, softening was observed by microhardness tests,

which usually corresponded to enhanced wear [l] 1

. The influence of

preconditioning diminished during the course of wear as the wear track

depth into the specimen increased.

One serious limitation with dental polymers is that the curing process

terminates at a low degree of conversion at the in situ temperature

(37 °C)

.

With the free-radical activated processes the increase of

viscosity during polymerization inhibits molecular diffusion which, in

turn, prevents the proximation of reactive species, which, in the

meantime, are used up by oxidation. We have found that increasing the

degree of cure decreased the extent of softening and improved the wear • resistance of the specimens which would otherwise be damaged from

preconditioning [2]

.

The degree of cure was enhanced by simply elevating

the cure temperature.

Since a sufficient elevation in temperature would be impracticable for in

situ placed restorations, a more difficult and sophisticated approach

involving changes in chemical structure is one of our current activities

as explained later in this chapter and Part I, Section F. It has to be

remembered; however, that increasing the degree of cure may

commensurately increase the polymerization shrinkage, which may lead to a greater loss of marginal integratity in application.

The inorganic reinforcing filler was evaluated by preconditioning

commercial dental composite specimens in weak intraoral acids which have

damage potential to the filler and the interface. Composites employing

modified glasses with alkaline earth elements to obtain radiopacity were

more sensitive than the pure silica reinforced composites. It was determined that stress corrosion plays an important role in the

degradation of composite restorations as evident from the leaching

experiments of Soderholm [3,4] and the wear and hardness measurements

made at MBS [5]

.

Since glass-ionomer cements have good bonding properties to dental tissue

[6]

,

it was decided to include the evaluation of their wear behavior in our studies. The cure process of the glass-ionomer cements does not seem

to be as viscosity limited as with the resin-based composites.

1 Figures in brackets designate references included at the end of this

chapter

.

53
Accordingly, higher degrees of cure can be reached at the in situ

temperature with the former.

With the three commercial glass-ionomer materials studied, the wear resistance of the water-preconditioned specimens was good except that the

incidence of catastrophic failure from brittle fracture during wear was frequent [7] . Specimens preconditioned in dilute lactic acid revealed

considerable chemical dissolution as apparent from electron micrographs

and accelerated wear. More recent work [8] on a commercial silver-filled

glass-ionomer cement showed that although the wear resistance improved

considerably, the susceptibility to brittle fracture and chemical

dissolution in lactic acid were still serious problems. These problems

stress the need for appropriate modifications in the composition and

structure of this class of materials for enhanced durability as will be

discussed later in this chapter.

PROGRESS REPORT

Phase I. Recent commercial composites which appear promising for

posterior occlusal application.

Mo experimental activity work in Phase I was undertaken during this

reporting period. Our past work on commercial composites provided

a sufficient basis to initiate research on MBS experimental

composites. During this reporting period,' however, a manuscript

concerned with the wear of selected commercial composites

* preconditioned in relevant organic solvents was completed and

published in the Journal of Dental Research [1] . At a later time

we will very likely conduct some evaluations of selected commercial

posterior composites.

Phase II. Experimental Composites with Flexible Polymers

The specific objective of this task was to obtain a multifunctional

polymer matrix with a high degree of cure (at in situ temperature)

,

a low solubility parameter, and low polymerization shrinkage. The

first experimental composite used in this study was a hydrophobic,

flexible resin comprising 70 wt % poly (fluorourethane methacrylate)

(PFUMA) and a siloxane diluent bis (methacryloxypropyl)

tetramethyldisiloxane (BIS-MPTMS) . These were mixed with a silanized fused-quartz filler. (For further details of structure

and composition, see Part I, Section F of this report and Reference

[9].) The polymerization shrinkage was reduced by using a prepolymer of PFUMA having about 20 repeat units corresponding to a molecular weight of about 12,000.

The results for the PFUMA/BXS-MPTMS system are shown on Fig. 1,

which includes the Xnoop Hardness Ratio, pf/pt; the early wear, ss

;

and the steady state wear, ms . pi is the initial hardness before

preconditioning in the selected media, and Df , after, ss is the wear at five hours, and ms is the asymptotic steady-state wear rate.

The preconditioning media were water and pure ethanol. From the

59
hardness ratio data, it is apparent that considerable matrix

softening results from the penetration of ethanol- On the other

hand, both wear quantities are essentially unaffected. This result

is attributed to the high degree of crosslinking which, in this

case, permits some diffusion, but very limited dissolution from

organic solvents.

The results of this work were presented before the IADR Conference

at the Hague [10] and a manuscript was presented to the Dental

Materials Group (DMG) microfilm series.

Although the wear of the PFUMA/BIS-MPTMS system appears to be

unaffected by ethanol preconditioning, the absolute hardness (not

shown in Fig. 1) is less and the wear much larger than that

observed for the more conventional resin-based composites. For

this reason we have initiated a study involving a composite with a resin of a higher flourine content and greater flexibility. The

system currently under study is a 70/30 mixture of

poly (f luoromethacrylate) (PFMA) and 10-decamethylene dimethacrylate

(DMDMA) diluent. (See Part I, Section F and Reference [9].)

Phase III. Glass-ionomer cements: conventional, metal-filled, and

modified experimental.

The experimental work on the commercial glass-ionomer cements,

including several conventional ones and one metal filled, was completed during the last reporting period. This year a manuscript

concerned with the wear of the conventional glass-ionomer cements

was prepared and was submitted to the Journal of Dental Research.

The work on the metal-filled system was presented before the AADR

Conference and a manuscript was submitted to the DMG microfilm

series. [8] A similar manuscript has been approved by the

Washington Editorial Review Board (VERB) for archival publication.

The conclusions are that these materials need modifications to

produce properties necessary for posterior application. The work

on some experimental modified glass-ionomer cements, referred to

here as hybrid cement-composites was initiated during this period.

The so called hybrid cement-composites (HCC) formulated at MBS are designed to overcome the deficiencies of glass-ionomer cements,

namely, susceptibility to brittle fracture and dissolution in

intraoral acids. The experimental system (HCC) contained a watersoluble monomer, 2-hydroxyethyl methacrylate (HEMA) in the liquid

(to be mixed with the powder) with appropriate catalysts added to a conventional glass-ionomer cement powder (See Part I, Section F)

After mixing, the two reactions (polymerization of HEMA and glassionomer cement) occur simultaneously producing a "rubber toughened"

glass-ionomer cement-composite which is more flexible than the

conventional glass-ionomer cements. The experimental results on the HCC specimens showed that the wear rate was slightly larger

than that for the conventional glass-ionomer cement, but brittle

60
failures were absent. In addition, unlike the conventional glassionomer cements, the hardness was unchanged, and the wear was not

enhanced from preconditioning in organic solvents and weak

intraoral acids.

The results of this work were presented before the IADR Conference

at the Hague [10] and a manuscript was submitted to the DMG

microfilm series.

Phase IV. Susceptibility of Commercial Dental Composites to Topical

Fluoride Gels.

Another specific source of damage is from the application of

topical fluoride gels, which may eventually reach composite

restorations even though not applied to them directly. In this

connection collaborative efforts were started with the University

of Maryland (UMd) Dental School at Baltimore to determine the

effects of various topical fluorides on wear of composite resins.

Using the NBS pin-on-disc wear apparatus, no significant

differences in wear of a silicon dioxide microfil were noted

following treatment with 10 six-minute imersions in either water,

1.23% acidulated phosphate fluoride (APF) gel (12,200 ppm) or 0.5%

APF gel (5,000 ppm). A composite resin with barium boroaluminum

silicate filler is currently being tested.

Since the modif ied-glass fillers using alkaline earth elements to

achieve radiopacity are more subject to chemical dissolutions in

weak acids, some sensitivity to the APF Gels with the barium

boroaluminum silicate filler is anticipated. Corresponding

clinical tests are being conducted at the (UMd) Dental School.

Phase V. Experimental Studies on Experimental Composites Employing

Apatite Reinforcing Fillers

This phase has not been initiated as yet. As stated earlier

radiopaque composite fillers employing alkaline-earth modified

glasses are subject to stress from the intra-oral environment

during wear. The conjecture is that corresponding apatites, e.g.,

barium will satisfactorily satisfy the radiopacity requirements and

be essentially insensitive to stress corrosion.

B. Glass Transition Temperature (Tg) of Matrix Polymers

There was no experimental activity on this project during this period.

For details on Background, Objective, and Progress Report, see Reference

[9] . A manuscript including the results of Tg measurements as a function

of cure time on pure BIS-GMA and 70/30 (wt/wt) 3IS-GMA/TEGDMA was prepared and submitted to VERB during this reporting period.

61
c. Wear Instrumentation (New Task)

Background

The wear measurements mentioned throughout this chapter were made using a pin on disc apparatus described in Reference [11] . The original version

was designed and assembled at the University of Indiana [12] . A second

version was constructed at the National Bureau of Standards and

essentially completed in 1976. This version was automatic, being

programmed on a tape, but did not involve a central processing unit

(CPU) . The mechanical portion of the apparatus (involving unique

components manufactured at NBS) was reinterf aced, and a programmable

instrumentation controller with a CPU was incorporated [11] . This

modification resulted in a more convenient, flexible, and reliable

system, which has been used up to the present time. The next version is now being considered, for which the salient features are described below.

Phase I. Methodology for improved wear apparatus

As a consequence of increased demand and modified methodology in

dental wear measurements, a new pin on disc wear apparatus is being

designed, and some of the commercially available components have

been purchased in FY 1986. The new version calls for independent

stepping motors as drives for the rotating specimen discs and other

mechanical controls. These motors are fully programmable with

respect to angle, rate, and function, e.g., constant speed, sine

function, ramps, or steps. They also eliminate the need for the

positioning scanners used in the present version. If funding

permits, instrumentation will be provided to measure friction

during the course of wear in this connection. Torque monitoring

devices are now commercially available. An important feature to be

incorporated is the facility to conduct submerged wear tests in

selected media (in the present version, fresh distilled water at 37

°C flows over the specimen surface continuously). An effort will

be made to use generic commercial components and modular devices as much as possible to facilitate repair and replacement of defective

components

.

Recently, some of the components of the present version were damaged by a transient in the electrical supply. Since there is some redundancy incorporated in the apparatus, and some repairs

were successful, reprogramming permitted us to continue our wear

studies; however, at some loss in performance and convenience. It now may become necessary to incorporate some of the new equipment

into the old version. This will, of course, slow down the

development and construction of the new apparatus in order to

continue wear studies currently in progress and planned.

62
D. Clinical Examinations Employing Removable Partial Dentures

Background

In vitro data obtained by McKinney and Wu [2] , as well as the results by

Wu and Fanconi [13] have shown that post curing of dental composite

resins increases the degree of conversion, and enhances the wear resistance of the composite resins.

In order to evaluate the clinical significance of the effects of post

cure of composite resins a clinical study was initiated in cooperation

with the American Dental Association using partial denture teeth as a vehicle for evaluation. The design of this study has been reported to

the AABR including the preliminary results after six months of in vivo

wear [14]

.

Accomplishments

Phase I. The retrieval of all denture teeth with composite resin

restorations and replacement of these teeth with new denture teeth and

establishing proper masticatory and esthetic function of the prostheses.

The entire clinical aspect of this study has been completed.

Phase II.

(a) Photograph under low power magnification (20X or 1:1 on film)

the retrieved restorations: in order to have a record of

discoloration.

(b) Clinically evaluate the restorations with a dental explorer

and visually for degree of wear.

3oth aspects of Phase II have been completed and results have been

reported at the IADR, The Hague, The Netherlands June 26-23, 1986.

A summary of the data is shown in the following table. Data are given for four dental composite resins: the number of pairs refers

to the number of sample pairs for the entire patient population

(each sample was paired with a control) . The score represents the

difference in wear between sample and control, averaged over the

entire set. The percent restorations represents the fraction of

all restorations (experimental and control) that showed signs of

clinical wear.

63
TABLE 1

Composite # Pairs

Clinical Difference in wear. Score (Percent)

Percentage of

Restorations Showing Wear

I 29 +4 (+5) 29

II 32 -6 (-6) 27

III 30 -1 (-1) 22

IV 29 +5 (+6) 16

Phase IY (Still to be completed)

(a) Evaluate whether technology developed by the MBS Materials

Science Division for measuring galling of metals can be

applied to the surfaces of denture teeth. If so, then

(b) Obtain quantitative data about the volume of material lost

for each composite restoration and obtain a measure of the

surface roughness by means of computer aided prof ilometry

.

Phase V (Still to be completed)

Evaluate and record surface appearance with SEM.

64
References

[1] McKinney, J.E. and Wu, W. Chemical softening and wear of dental

composites. J. Dent. Res. 64 1326-1331 (1985).

[2] McKinney, J.E. and Wu, W. Effect of degree of cure on hardness and wear

on three commercial dental composites. AADR Abstr. 62? 285, Abstr. 1047

(1983).

[3] Soderholm, K.J.M. Degradating of glass filler in experimental composites.

J. Dent. Res. 60 1867-1875 (1981).

[4] Soderholm, K.J.M. Leaking of fillers in dental composites, ibid 62 126-

130 (1983) .

[5] McKinney, J.E. Influence of acids of wear of composite restoratives.

IADR Abstr. 63 199, Abstr. 256 (1984).

[6] Hots, P., McLean, J.W., Seed, I., and Wilson, A.D. The bonding of glass

lonomer cements to metal and tooth substrates. Br. Dent. J. 143 41-47

(1977).

[7] McKinney, J.E. , Antonucci, J.M., and Rupp, N.W. Wear and microhardness of

ionomer cements. IADR Abstr. 64 371, Abstr. 1967 (1985).

[3] McKinney, J.S., Antonucci, J.M. and Rupp, N.W. Wear and microhardness of

a metal filled ionomer cement. AADR Abstr ^5 344, Abstr. 1577 (1986).

[9] Tesk, J. , Antonucci , J., Brauer, G., McKinney, J., Penn, R., Stansbury,

J., de Rijk, W., Venz, S., Okuno, 0. and lizuka, H. Properties and

Interactions of Oral Structures and Restorative Materials, NBSIR 86-337

(1986) .

[10] McKinney, J.E. and Antonucci, J.M. Wear and microhardness of two

experimental dental composites. IADR Abstr. 6_5 344, Abstr. 1101 (1986).

[11] McKinney, J.E. Apparatus for measuring wear of dental composites. Wear

76 337-347 (1982)

.

[12] Powell, J.M., Phillips, R.W., and Norman, R.D. In vitro wear response of

composite resin, amalgam, and enamel. J. Dent. Res. 54 1133-1185 (1975).

[13] Wu, W. and Fanconi, B.M. Post curing of dental restorative resin.

Polymer Engineering and Science 23 704-707, (1983).

[14] de Rijk, W.G., Conner, M.L., Jennings, K.A., and Wu, W.L. The in vivo

wear resistance of dental composites with enhanced polymerization. J. Dent. Res. 63 Abstr. # 951 (1984).

65
Publications

McKinney, J.E. and Wu, W. Chemical softening and wear of dental composites, J. Dent. Res., 64 1326-1331 (1985).

McKinney, J.E. Environomental damage and wear of dental composite

restoratives. In "Posterior Composite Resin Dental Restorative Materials", G.

Vanherle and D.C. Smith, eds., 3M Company, 331-349 (1985).

Manuscripts Under Review

McKinney, J.E., Antonucci, J.M., and Rupp, N.W. Wear and microhardness of

glass-ionomer cement. J. Dent. Res.

Whitman, D.J., McKinney, J.E., Hinman, R.W., Hesby, R.A. and Pelleu, G.B. In

vitro wear rates of three types of commercial denture tooth materials. J. Prosth. Dentistry. In Press.

Contributed Talks

McKinney, J.E., Antonucci, J.M., and Rupp, N.W. Wear and microhardness of a metal-filled ionoraer cement. AADR Abstr-. 65_ 344, Abstr. No. 1577 (1986).

McKinney, J.E. and Antonucci, J.M. Wear and microhardness of two experimental

dental composites. IADR Abstr. 65 848, Abstr. No. 1101 (1986).

ae Rijk, W.G., Conner, M.L. and Jennings, K.A. The in-vivo wear resistance of

dental composites with enhanced polymerization, IADR meeting (1986) .

Manuscript Approved by WERB

McKinney, J.E., Antonucci, J.M., and Rupp, N.W. Wear and microhardness of a metal-filled glass-ionomer cement.

Manuscript Submitted to WERB

Wu, W. , Yu, C.C., and McKinney, J.E. Glass transition temperature of dental

composite resins.

66
Pf/Pl

o o o o o •-*> • » 0 ® • « e O Pd O) GO o

>

S5 ( /itn )

m s( nm/rev

)

o -- ro q 4s cn a) xi

wmmm

Figure 1: Hardness ratio, P-/P. , early wear, Sg, and steady-state

wear rate, m

s

, for tne PFUMA/BIS-MPTMS experimental composite.

W , water preconditioned; E, ethanol precondi tioned

57
III. DENTAL ALLOYS, CERAMICS AND METROLOGY

Overview

The past decade has witnessed widely fluctuating costs for dental restorative

casting alloys. These have led to a large increase in the types of dental

alloys marketed as replacements for gold alloys. Porcelain-veneered cast fixed

partial dentures and drowns comprise a significant fraction of these protheses

fabricated. Because the newly introduced alloys can vary considerably in their

fabrication characteristics and clinical performance, more reliable methods

than now exist are desirable for evaluating their properties, both

independently and as systems with porcelain. The development of such

techniques will be of aid to the manufacturer and dental consumer in

understanding and controlling the factors which determine satisfactory clinical

performance. Of these, those considered to be of prime importance are that

porcelain-alloy thermal-stress compatibility, the porcelain-to-metal system

strength, alloy castabxlity and the attendant capability of producing good

fitting castings, and alloy solderability . Work has focussed on these subjects

with the objective of defining and confirming measurement techniques which will

be of ard in new product development, product control and evaluation.

A. Porcelain-Alloy Compatibility (Thermo-mechanical Stress)

PROGRESS REPORT

Overview

Residual stress from the porcelain firing cycle is considered to be a major factor leading to failure of porcelain fused-to-metal restorations.

This study is undertaken to clarify the parameters which are most

important in developing residual stress. These can include the thermoplastic properties of the porcelain, thermal conductivities, temperature

dependent elastic moduli, glass transition temperatures (porcelain) and

coefficients of thermal expansion.

Accomplishments

The objective of this part of the investigation was to explore the

potential of using the gap of a porcelain veneered split-metal ring as a means for determing the thermal stress compatibility between porcelain

and metal. It is hoped that ultimately tables of material properties

which correlate with gap change and calculated stress can be constructed.

At the very minimum, results of this investigation should help to

identify the major sources for the build-up of residual stress.

Phase I. Complete development of the required Finite Element Model (FEM)

and Program

A two dimensional FEM has been constructed which consists of 50

layers of material. The FEM program is first being used to study

the effects of material parameters for porcelain alone, cooled at

various rates. The model simulates the development of a

53
temperature distribution during cooling , examines the effects of

cooling rate on this temperature distribution, incorporates cooling

rate dependence for the glass transition temperature, Tg, a temperature dependent coefficient of thermal expansion below Tg and

a constant (but a manipuble variable) coefficient of thermal

expansion above Tg, and a temperature dependent elastic modulus for

the porcelain. The results are now being analyzed. One result

shows that less than a 1% difference exists between calculations

which incorporate a temperature dependent elastic modulus versus a constant value for elastic modulus.

Phase II.

At present, analyses are in progress on the sensitivity of

calculated stress (at the surface and center of the porcelain slab)

to material parameters such as coefficient of thermal conductivity,

temperature dependent shear viscosity, cooling rate dependence of

Tg and coefficients of thermal expansion. Following completion of

analysis of the stress for the multilayered porcelain slab, the

program will be modified to analyze a multimaterial problem

consisting of porcelain on metal. Results will be compared with

previously obtained results for the change in gap of porcelain

veneered split-metal rings [1]

.

Phase III

Finalization of material input parameters has been delayed due to

the complexity which was involved in developing the 50 layer FEM of

porcelain (see Phase I)

.

Phase IV

Devise simple analytical representation of stress-strain in

porcelain metal systems, if possible, for a split ring. This will

follow Phases I-III.

3.

Phase V

Compare results of FEM vs theory developed by Scherer.

Porcelain-Alloy Compatibility

PROGRESS REPORT

[ 2 ]

Overview

A bending beam composite specimen was designed to produce quantitative

measurements of the tensile strength of dental porcelain f used-to-metal

systems. This system permits the production of test specimens with

materials and equipment present in most commercial dental laboratories,

providing an expedient evaluation method for PFM systems.

69
Multiple fracture data can be obtained from a single sample, making some

form of ordered statistics a necessary part of the data evaluation.

70
Accomplishments

Phase II

Determine three dimensional and two dimensional Finite Element

Model (FEM) of Bending Beam Composite (BBC) . This has been

completed. However, on the basis of new work in progress on stress

in porcelain-metal systems (see Part A, Thermo-mechanical Stress)

,

this work will continued toward a new FEM which includes the

variables of temperature dependent material properties etc., as discussed in Part A.

Phase III

The fracture data for the PFM systems have been evaluated assuming

a two parameter Weibull distribution. The data have been evaluated

both by curve fitting (CV) , by using the most likely estimate (MLE)

and the best linear unbiased estimate (BLU) . The Weibull

parameters and the scale parameters have been determined. The test

results are presented in Table I.

A confidence limit for the values has been calculated from the

tables by Thoraan et al [3]. The values are listed in Table 2.

Other than System II, the agreement between the values obtained by

the two methods is satisfactory.

The agreement between experimental and theoretical values is shown

in Figures 9-10. The m = 9 value indicates that the distribution

of the failure stresses is definitely not normal; but follows the

Weibull distribution for a brittle material. (Rice and Ruff have

shown, a Weibul parameter of m=3.5 produces a probability

distribution similar to the normal distribution.)

The same algorithms have been tried on composite resin bonding data

by Thompson et al [4] and it was found that again a non-normal

distribution (m=l) , i.e., the exponential distribution described

the data.

It would seem that the algorithms developed for the evaluation of

PFM systems may find wider application than just this one instance.

The above section pertains to Phase III as stated in NBSIR 36-3320

[4]

.

For future work a continuation is seen, particular in the

resolution of the discrepancy between the parameters obtained by curve fitting and those obtained by maximum likelihood estimates.

Phase IV

Algorithms that show agreement in the Weibull parameters obtained

by different methods such as curve fittings and point estimates.

71
Phase V

Determine the conditions for and the confidence limits associated

with complete and censored data sets.

Phave VI

Develop an algorithm to incorporate the sample shape factor into

the point estimate routine of the computer.

C. Castabilitv (Filling of a Mold with Cast Dental Alloy)

PROGRESS REPORT

Overview

Because of the many dental alloys appearing on the market there has

existed the need for an uncomplicated and expedient method of evaluating

casting behavior and for determining the most favorable conditions for

their performance. Such a method can be useful in the selection of new materials, in dental laboratory and manufacturing process control and in

the design of new alloys.

Numerous methods have been proposed in the past for determining various

aspects of the casting of dental alloys. A number of procedures have

• been proposed. These have been discussed in NBSIR 86-3320 [6] .

A primary effort at NBS has been the development of a method for

evaluating the ability to cast an alloy to fill a mold under prescribed

casting conditions. For this purpose a method employed a polyester-grid

mesh pattern has been chosen to embrace the following requirements.

(1) The procedure should provide a measurement of the capability of an alloy to fill a mold.

(2) The method should make use of equipment, facilities, and materials

generally available to the dental industry.

(3) The experimental conditions found in dental prosthetic laboratories

should be duplicated.

(4) The pattern and mold should be easily produced.

(5) The manner of evaluating the casting should be objective and

accomplished without the need for sophisticated measuring

instruments

.

(6) The method should be sensitive to materials, temperature,

techniques, or other variables affecting castability. Hinman et al

[7]

have reported on a method which meets these requirements.

72
Accomplishments

Phase I

A manuscript, "Castability of Dental Alloys, Mold and Alloy

Temperature Effects” has been submitted to the Journal of Dental

Materials for publication.

Phase II. Analysis of Effects of Composition on Castability.

This work has been refined, with the addition of data from the

casting of alloys under controlled-variables conditions.

The alloy compositions were designed to avoid statistically

correlated affects of compositional changes (for example, simple

doubling of the amounts of two elements from one alloy to another)

so that chemically relevant effects could be observed. The

following equation has been used.

+ ki (Mo) + k2 (Si) + k3 (Nb)

+ k3 (AL) + k& (Be ) + k? (Be X St )

where the terms within the parenthesis are the elemental

compositions in weight percent and each K reflects the

effectiveness of each element.

C v t is the transformed castability value [4]. Because Cvt is a function of alloy casting temperature Ta and mold temperature Tm,

each K is also a function of those same variables. The K's are shown on Figs. 1-8. These figures show the relative importance of

each element at various temperatures.

From the figures it is obvious that B and Be have the largest

effects on increasing Cv (through Cvt). The effect of higher mold

temperature on K4 for B is to slightly decrease Cvt , while alloy

casting temperatures have virtually no effect on X4 . For Be,

higher mold temperatures result in greatly higher values of Ke while casting temperatures have only a small effect.

The exact reasons for the behavior of and Ke with temperature

are, of course, not known, but it is possible to infer something

about reactions between the alloys and investments, and the

oxidation of the melts. For example, an increase of an alloy's

chemical reaction with the investment will cause wetability to

increase and the castability value might correspondingly be

increased due to this. On the other hand, an increase in the

amount of oxide film on the advancing front of the cast melt

73
surface should make it more difficult for the melt to flow easily

as the oxide film could be expected to resist the moving of the

alloy; this should tend to cause a decrease in the castability

value- With these thoughts in mind, one may hypothesize about why

increasing mold temperature results in a decreasing value of K4 for

B and in an increasing value of Ks for Be. Higher mold

temperatures might tend to cause more oxidation of B on the melt

surface while Be might interact more with the investment- It

should be kept in mind that in the case of increasing mold

temperature, only the advancing liquid alloy in close contact with

the mold will drop quickly in temperature as the alloy moves through the mold. The temperature and the fluidity of the melt

which follows should not be as drastically changed.

When the casting temperature of the alloy increases, the

temperature of a the advancing melt correspondingly increases. An

increasing casting temperature affects not only the chemical

reactions, but also the fluidity of the melts. It is, therefore,

difficult to conjecture more about the complex relations between

the Ki's and casting temperature. How much the fluidity changes

and how much oxidation or interaction with the mold occurs with

increasing casting temperature is not known. Ki must reflect the

net balance in these and other factors perhaps not even considered.

Similar types of inferences can be made regarding the effects of

aluminum (Ka), NB, (K3), and all of the other elements on the

castability value.

One interesting feature is the apparently synergistic effect seen between Si and Be; this is the largest effect of all as may be seen through the value of K7 . Note, however, that for 0.1 wt % each of

Be and Si, the large K? is multiplied by only 0.01 in equation 3,

if Be and Si present are each increased by a factor of 5 to 0.5

wt %, K? is multiplied by 0.25, a net increase of 25. Hence, Cvt

and Cv can be highly sensitive to change in the combination of

these elements. This result suggests that the product of these

elements is an important factor in control of the quality of alloys

having both these elements.

The results of this study were obtained by assuming linear effects

on Cvt with changes in composition. Because Cvt and Cv are almost

linearly related throughout most of the range of Cv (0.1 <. Cv <_ 0.9), this is equivalent to assuming ideal solution behavior.

Examination of binary phase diagrams such as Ni-B and Ni-Al shows

this condition is not likely to extend very far for some elements

which cause precipitation at low concentrations. This should be

kept in mind if the data are used to predict changes in Cvt with

changes in composition. It is the simplest and most wieldy

assumption; however, and facilitates the calculations, the results

of which provide some insight into casting temperature, mold

temperature, and investment effects. Another point that should be

kept in mind is that these results were all obtained with one particular phosphate bonded investment. As will be shown in a

74
paper in preparation, the constants in equation 1 can be affected

by the investment. This may be expected in the light of the

previous discussion. For example, if an alloy with B is used in an investment (or with a pattern coat) that discourages interaction

between the investment and the alloy, the castability value might

increase. Other factors, of course, such as particle size

distribution and permeability of the investment could be expected

to affect Cvt

.

A previous paper (4) has shown that batches of the same investment can affect the values of Cvt through changes in the

intercept, a, of equation 1, but that the temperature coefficient,

b, is not affected.

With the aforementioned points in mind, equation 3 may be useful

for computer aided design of Ni-Cr alloys. The calculated changes

in the castability value as a function of mold and alloy

temperature can be balanced against practical factors such as temperature limitations and/or hot tearing as well as grain size,

corrosion resistance, surface finish, strength and so forth. In

using equation 3 for design of new alloys a method for estimating

Ts must be used. One such equation has been developed and is under

further review at this time.

The most important aspect of this work is considered to lie in the

demonstration of the method for using data acquired with the mesh

monitor to gain further insight into the complex effects occurring

during casting and to show how the results can be used. For design

of new alloys these methods may be applied to other alloy systems.

D. Castability (Accuracy of Fit of Dental Castings)

PROGRESS REPORT

Overview

In light of the results obtained by Eden et al [8]

,

Warsaw [9] , and

Meiser [10] the need for a better understanding of the role of the

setting expansion of a dental casting investment in the production of a cast prosthesis that fits becomes more and more prominent.

Previous measurements here indicate that the expansion during the setting

at the site of the wax pattern is significantly less than the expansion

observed by the change of the external dimensions of the setting

investment

.

Accomplishments

The results obtained by Reiser et al. have proven to be reproducible by

R. Engler et al. A design change has been incorporated in the experiment

to reduce variability in the experiment, in order to reduce fluctuations

in the measurements during the pour of the investment.

The standard deviation of the resulting data has been significantly

75
reduced by the design modification while confirming the results obtained

by Meiser. (The results have been presented at the General Session at

the AADR and the DMG microfilm.)

Experiments have been continued with the use of multidirectional strain

gauges. These gauges are comprised of four individual gauges in a Wheatstone Bridge configuration spatially oriented such that the

electrical signal represents the differential strain between the X and Z direction. The multidirectional gauge was placed such that the x direction was radially placed in the casting ring with the z direction

parallel to the cylindrical axis.

It was found that the difference between the axes, x, and z was -0.02% (+

0.08) a value undistinguishable from 0 (with our experimental detection

limit of approximately 0.01%) or the scatter in the data.

A manuscript describing these results has been submitted to the Journal

of Prosthetic Dentistry.

Phase I

(a) The design of cellulose acetate wings attached to the strain gauge

substrate has met all the objectives set forth in the workplan.

The zero drift during the investing process is now small compared

to the overall setting expansion (0.15%).

(b) The differential setting expansion in three dimensions has been

evaluated. The casting ring is cylindrically symmetric; hence, x and y directions are identical (the z direction is the cylindrical

axis) . Therefore, measurements in only the x and z directions are needed. It was found that with a Kaowool Liner no difference is

observed between the x and z directions.

Metrology and Clinical Performance

PROGRESS REPORT

Overview

This part of the program involves an investigation of the application of

the disciplines of fracture mechanics and the statistical theory of

fracture to the study of dental materials. The tecniques to be used are applicable to any materials which are subject to failure by a brittle

crack growth mechanism.

The use of such techniques can be expected to eliminate or at least

reduce the effects of experimental artifacts on test results due to

differences of specimen size, geometry of loading, etc. The first part

of the program can be described as a study of the strength of composite

restorative materials.

76
Objective

The objective of this project was to apply the concept of fracture

statistics: "that fracture initiates at a worst inherent flaw when it is

subjected to its critical stress", to obtain information about the

underlying flaw distribution. Four studies have been undertaken: (1)

Specimen size effects in the diametral tensile test (DTT) , (2) The

effects of loading geometry of rectangular beams, (3) The effect of

exposure of DTT specimens to food simulating fluids, and (4) An

investigation of the precision of parameter estimation for the Weibull

distribution.

Accomplishments

Phase I. The effects of specimen size on the diametral tensile strength

of composite restoratives.

Using Weibull's concept of the statistical nature of the failure of

brittle materials (11,12) we have investigated the specimen size

effect in the diametral tensile test for one experimental

composite. Both standard size ( 6 mm dia x 3 mm ) and small ( 3 mm

dia x 2 mm ) specimens were tested. The results for the small

specimens are plotted as a cumulative distribution function in

Figure 11 where they are fitted by the Weibull distribution

function with the parameters shown. The results for the standard

sized specimens are plotted in Figure 12 along with distributions

calculated from that of Figure 1 by means of the weakest link

formula:

1 - F = ( 1 - Fo ) a

where n is the multiple of the number of flaws in the small

specimens which is thought to be contained in the standard

specimens and Fo is the distribution function for the small

specimens

.

The agreement of the data with the curve for n = 2 is quite

remarkable. Although the large specimens have four times the

surface area and six times the volume they apparently contain only

twice as many effective flaws as the small specimens.

Attempts to reproduce this result with another material have

failed. The smaller specimens actually showed lower strength than

the standard specimens. This might be explained by differences in

the manner of specimen preparation, A more rapid heat flow from

the smaller specimens which probably occurred during polymerization

would cause them to polymerize at lower temperature and thus to

attain a lower degree of cure. In the first experiment ( reported

above ) the small specimens were cured in poly ( tetra

f louroethylene ) molds while in the latter experiments molds for

both sizes were of metal. The PTFE, having a lower thermal

conductivity, may have retarded the heat flow allowing the small

77
specimens to attain a larger part of the strength that might be

expected due to the specimen size effect. These results

dramatically show the effect of experimental procedures/conditions

on the test results obtained.

Phase II. The strength distribution of beams of rectangular cross

section.

Another experiment that should be capable of distinguishing

between surface flaws and volume flaws involves the bending of

beams of rectangular (non-square) cross section in each of two

orientations one with the bending axis perpendicular to the height

(h) the other with the bending axis perpendicular to the width (w)

.

One must first integrate Weibull' s risk of rupture equation over

the non-uniform stress distribution assumed for the bent beam

(12) . In the integral for flaws distributed throughout the volume

of the material, h and w appear symmetrically and one should

observe no difference m characteristic stress for the two

orientations. However for flaws distributed on the surface of the

specimen the height of the beam is weighted as 1/m+l where m is

the Weibull exponent or modulus and one should observe a different

characteristic stress for the two orientations.

Specimens were prepared from Visiofil (Espe) , a conventional

composite restorative, ( 1 mm x 4 mm x 25 mm) and broken in four

point bending. The ratio of the characteristic stresses observed

was 1.108 + .05. That predicted by Weibull theory is 1.107. When

the experiment was repeated using Visiodispers (Espe) , a microfilled material, the ratio obtained was 0.90 + .04, a result

that cannot be explained by Weibull theory.

One can speculate that this result might be due to the nature of

the fracture produced when removing mold flash from the specimens.

If in the microfilled Visiodispers specimens these fractures

produced flaws which reduced the flexural strength while with the

conventionally filled Visiofil they did not these results can be

explained. This argument can be reinforced by observing that the more serious flashes were found along both edges of one side of

each specimen. Thus with the beam in the vertical orientation one

of these flashes is always on the tensioned face of the specimen

while with the beam in the horizontal orientation there are either

both or neither of the flashed edges on the tensioned face. From

this one would expect a much wider distribution of strengths for

the horizontal specimens than for the vertical. This was observed

for the Visiodispers specimens but not for the Visiofil specimens.

The result does indicate that some composite formulations are more sensitive to flash or finishing of restorations. This sensitivity

could be important in the design of restorative materials which

will have greater marginal integrity.

78
Phase III. Investigation of the effect of food simulating fluids on the

strength distribution in composite restorative materials.

One hundred twenty-six diametral tensile test (DTT) specimens were prepared from Adaptic (Johnson & Johnson) . One third of these were stored in de-ionized water, one third in 70% ethanol and one third

in n-heptane. After two weeks they were tested. The distributions

of failure stresses were in all cases found to be irregular. When

plotted on Weibull coordinates they were concave upward. This is

thought to indicate that the underlying distribution of flaws is

composed of two distinct populations such as, perhaps surface

flaws and volume flaws. If the two distributions are represented

as:

Fi = 1 - exp- (s/si

)

Fa = 1 - exp-(s/sz) m2

then, assuming statistical independence of the two populations,

the combined distribution, F, will be related to them as:

1 - F = ( 1 - Fr ) ( 1 “ Fa ) .

The experimental data was fitted to F by a non-linear least

squares technique to determine the constants si, ml, s2, and m2.

The derived distributions are shown in Figure 13. It would appear

that compared to the water treatment, the alcohol treatment

weakened only that population of flaws with the higher

characteristic stress, while treatment with heptane weakened both

populations about equally. The results demonstrate the importance

of environment on the strength of dental composites.

Phase IV. An investigation of the precision of parameter estimation for

the Weibull distribution.

Since the distributions encountered in fracture studies are frequently not normal another more versatile function is commonly

used. This function has come to be known as the Veibull

distribution:

F = 1 - exp -( s/so - su/so )®

F is the cumulative distribution function of the fracture stress s; m is the modulus or shape parameter; so is the scale or position

parameter; and s u is the cut off parameter. This function can represent distributions which are skewed to the left or to the

right. It can be easily inverted. It can be easily differentiated

to obtain the probability density function ( f ) . It can be readily

multiplied by another similar function. It can be raised to a power. All of these operations are very difficult with the normal

distribution.

79
To estimate the parameters of a distribution from a particular

sample taken from that distribution the preferred technique is

known as the method of maximum likelyhood. This technique

determines estimates of the parameters m, so , and s u that will

maximize the likelyhood function which is the probability of

obtaining that particular sample or set of independent selections

from the distribution. This technique is preferred because it

enables one to include censored data where it is known only that a particular test result is greater or less than some value but with

the exact result unknown.

For the present study we can set so = 1 and s u = 0 and sample from

the resulting distribution. This is done by generating random

values for F from the uniform distribution and solving for the

corresponding s. Samples were taken of size N = 5, 10, 20, 40, and

30 from distributions with exponents m = 2, 4, 3, and 16. Fifty

such samples were taken for each of the twenty combinations of N

and m. Estimates of m and so , <m> and <so> were then determined by

the maximum likelyhood technique for each of the twenty sets. The

estimates were found to be distributed non-normally around the

values of m and so = 1. The distributions of <m> and <so> were found to be well described by three parameter Weibull functions.

From these functions the tenth and ninetieth percentile points were determined. These 'are plotted in Figures 14 and 15 for <m> and <so> respectively for the values of m and the sample sizes used. From

Figure 14 it is seen that the distribution of <m>/m is nearly

independent of the value of m while in Figure 15 the distribution

of <so>/so depends strongly on the value of m for the distribution

from which the samples were taken. These curves and similar ones

for other percentiles can be used for the testing of hypotheses and

assigning confidence intervals for Weibull parameters.

30
References

[1] Tesk, J.A., Whitlock, R.P., Widera, G.E.O., Holmes, A., and Perry, E.E.

Consideration of some factors influencing compatibility of dental

porcelains and alloys. Part II, Porcelain Alloy Stress, Proceedings of

the 4th International Precious Metals Conference, Toronto, Canada,

Pergammon Press, 283-291 (1980).

[2] Scherer, G.W. Viscoelastic Analysis of the Split Ring Seal, J. Am.

Ceramic Soc. Vol. 66 #2, 135-139, February, (1983).

[3] Thoman, D.R., Bain, L.J. and Antle, Reliability and Tolerance Limits in

the Weibull Distribution, Techometrics , 12, 363-371, (1970).

[4] Thompson, V.P. and de Rijk, V.G. Statistical Distributions of Tensile

adhesive bondstrengths , J. Dent. Res. 65 Abstracts AADR #613 237, March,

1986.

[5] Rust, S.W. and Rice, R.C. Statistical distribution, ASM Metals Handbook,

9th Ed., 8, American Society for Metals, Metals Park, OH 628-638 (1986).

[6] Tesk, J.A., Antonucci, J.A. , Brauer, G., McKinney, J., Penn, R.,

Stansbury?, J., de Rijk, W., Venz, J., Okunc, 0., and Xizuka, H. Properties and Interactions of Oral Structures and Restorative Materials.

Annual Report of NIDR for 1985. NBSIR 86-3320, National Bureau of

Standards (1986)

.

[7] Tesk, J. A. , Whitlock, R.R., Parry, E.E. and Durkowski, J.S. A technique

for characterizing casting behavior of dental alloys. J. Dent. Res. 64

134-138 (1985).

[8] Eden, G.T., Franklin, J.M., Ohta, Y., and Dickson, G. Fit of porcelain

f used-to-metal crown and bridge castings, J. Dent. Res. 53_ 12 (1979).

[9] Marsaw, F.A., de Rijk, W.G., Hesby, R.A., Hinman, R.W., and Pellen, G.3.

Internal volumetric setting expansion of casting investments. J. Prosthet. Dent., 52, 361 (1984).

[10] Meiser, E.T., de Rijk, W.G., Tesk, J.A., Hinman, R.W., Hesby, R.A., and

Pelleu, G.3. Internal setting expansion of a dental casting investment

measured with strain gauges. J. Prosth. Dent. 5_3 370-873 (1985).

[11] Weibull, W. A statistical theory of the strength of materials. Ingen.

Vet. Akad, Handlingar, Nr. 151 (1939).

[12] Weibull, W. The phenomenon of rupture in solids, Ingen. Vet. Akad,

Handlingar, Nr. 153 (1939).

[13] Weil, N. A. and Daniel, I.M. Analysis of fracture probabilites in

nonuniformity stressed brittle materials. J. Am. Cendum. Sci., 47, #6,

268-274 (1964).

31
Publications

Task, J.A., Antonucci, J.M., Brauer, G.M., McKinney, J.E., Penn, R., Venz, S.,

Iizukda, H., Okuno, 0., de Rijk, W. Properties and interactions of oral

structures and restorative materials, NBSIR 36-3320 (Feb. 1986).

Tesk, J. A role of straucture and composition on the physical and biological

properties of dental alloys. Review of literature for International Workshop

on Biocompatibility, Toxicity and Hypersensitivity to Alloy Systems Used in

Dentistry, Univ. of Michigan Press (1986) .

Tesk, J.A., Wa^erstrat, R.M. Dental base-metal casting alloys: physical

metallurgy. Encyclopedia of Matl. Sci. Eng. 1056 (1986).

Penn, R.W. A recording dilatometer for measuring polymerization shrinkage,

Dent. Mater. 2:78-79 (1986).

Manuscripts Under Review or Accepted for Publication

Kase, H.R. and Tesk, J.A. Elastic constants of three representative

nonprecious dental alloys. Submitted to J. Biomed. Materials Research.

Tesk, J.A., Widera, G.E.O., Hinman, R.W. and de Rijk, W.G. A porcelain-metal

composite specimen in determining system strength. Cleared WERB review, to be

submitted to Dental Materials Journal with companion paper (see next paper)

.

de Rijk, W.G., Tesk, J.A. and Conner, M. A quantative and expedient test for

the tensile strength of porcelain-to-metal systems - Part II. Experimental

procedures and results.

Penn, R.W., Craig, R.G., and Tesk, J.A. Diametral Tensile Strength and Dental

Composites. Submitted to Dental Materials.

Tesk, J.A., Okuno 0., and Penn R. Mesh Monitor Casting of Ni-Cr Alloys Element

Effects. Editorial Review

Okuno, 0., Tesk, J., and Penn R. Mesh Monitor Casting of Dental Alloys:

Investment Effects. Editorial Review

Sngler, R.A., de Rijk, W.G., Tesk, J.A. and Morris, D. Multidimensional

internal setting expansion of a phosphate-bonded casting investment measured

with strain gauges. Submitted to J. Prosth. Dentistry.

Tesk, J.A. Review of Paper - Casting Metals, by Kamal Asgar. Proceedings of

the International State-of-the-art conference on restorative materials at NIH.

In press.

de Rijk, W.G., 3rown, W.E. and Chow, L.C. The clinical evaluation of

ahydroxyapatite forming paste in the treatment of dental hypersensitivity.

Biomedical Engineering. Current Concepts VI, S. Saha. ed. Pergamon Press (in

press)

.

82
Bundy, K.J., and Penn, R.W. Improvement of metal/bone cement interfacial

strength. Submitted to J. Biomed. Mater. Res.

Invited Talks

Tesk, J.A. The dental space program, or; you said a mouthful. Johns Hopkins

University, March 1976.

Tesk, J.A. The use of a mesh eating monitor for control of dental laboratory

processes. Washington Section of the National Associatioin of Dental

Laboratories. March 1986.

Tesk, J.A. Review of paper by Kamal Asgar. Casting metals, presented at

International State-of-the-art conference on restorative materials at NIH,

Sept. 1986.

Tesk, J.A. The use of a mesh casting monitor for evaluation and control of

dental laboratory casting processes. Richmond Dental Laboratory Group,

Richmond, VA, Sept. 1986.

de Rijk, W. Dental adhesion, bonding or luting. Gordon Research Conference on the science of adhesion, Aug. 1986.

33
Contributed Talks

de Rijk, W.G. and Tesk, J.A. The distribution of failure stresses in

porcelain to metal systems, IADR/AADR meeting, March 1986.

Liao, R., Grolman, K., Thompson, V.P. and de Rijk, W.G. Adhesive Resins:

Tensile Bond to Metal and Resin Thickness Effects, IADR/AADR meeting, March

1986.

Thompson, V.P. and de Rijk, V. Statistical Distributions of Tensile Adhesive

Bond Strengths, IADR/AADR meeting, March 1986.

Sngler, R.A., de Rijk, W.G., Tesk, J.A. and Morris, D. Internal Setting

Expansion of a Phosphate Bonded Casting Investment Measured by Strain Gauges,

IADR/AADR meeting, March 1986.

Okuno, 0. and Tesk, J.A. Mesh Monitor Casting of Dental Alloys: Investment

Effects, IADR/AADR meeting, March 1986.

Tesk, J. A. , Okuno, 0., and Penn, R. Mesh Monitor Casting of Ni-Cr Alloys:

Element Effects.

Slew, C., Gruninger, S.E., Brauer, G.M. and Tesk, J.A. Biological Safety

Evaluation of Syringic Acid Ester Cement, IADR/AADR meeting, March 1986.

Natarajan, R., Widera, G.E.O., Min, 3.J., and Tesk, J.A. Residual Stress

Distribution in Metal Ceramic Crowns, IADR/AADR meeting, March 1986.

Penn,R.W. and Tesk, J.A. Fracture Statistics of the Diametral Tensile Test,

IADR/AADR meeting, March 1986.

Widera, G.E.O., Natarajan, R., Parthasarathi , T., and Tesk, J.A. Stress in

Cement Bonded Ceramic Crown Systems, IADR/AADR meeting, March 1986.

de Rijk, W.G., Jennings, K.A. and Menis, D.L. A Comparison of Chemical

Durability Test Solutions for Dental Porcelains, Society of Bioengineering

Conference, Oct. 1985.

84
Captions for Figs.

Fig. 1 to 8

The effect of casting temperature and mold temperature on the conef f icience,

ki , for the equation describing Cvt, (page 67)

35
K.x

10

1.0 Ni/Cr

I I I 1 I— 1

i

1

1 600 650 700 750 800 850 900 950 1000 Tm, Mold Temp. C

FIGURE 1

1350 1400 1450 1500 1550 1600 1650 1700

Tc, Casting Temp, rC

600 650 700 750 800 350 900 950 1000 Tm, Mold Temp, rc

FIGURE 2

36
600 650 700 750 800 850 900 950 1000 Tm, Mold Temp. /"C

FIGURE 3

I —- | i r iii*' 600 650 700 750 800 350 900 950 1000 Tm, Mold Temp, r C

FIGURE 4

37
K,x

10

8.0 -r1 9

I

1350 1400 1450 1500 1550 1600 1650 1700

Tc, Casting Temp. C

600 650 700 750 800 650 900 950 1000 Tm, Mold Temp. . C

FIGURE 5

1 lilt’ 1 600 650 TOO 750 300 350 900 950 1000 Tm, Mold Temp. rC

FIGURE 6 38
K

6x

80

Te, Casting Temp. C

|——,

1 —, | —T—

600 SSO 700 750 800 850 Tm, Mold Temp / C

SCO 950 1000

©

FIGURE 7

600 550

1 ~r 1 “

700 750 300 350 900 Tm. Mold Temp C

-T 1 950 1000

FIGURE 3 39
Table I

Results

Porcelain Metal m(MLE) m(MLE) m(CF)

System biased unbiased

I 3.2 4.2 5.1

II 5.0 7.2 10.0

III 6.7 9.2 9.0

IV 3.5 5.2 5.0

V 2.2 3.2 3.9

90
Table II

Resul ts

PM m(MLE) m(BLU) n Confidence Interval

System unbiased ( at a » 0.1)*

.

I 4.2 4.8 46 1.19

II 7.2 7.2 ' 27 1.28

III 9.2 9.8 26 1.28

IV 5.2 5.1 22 1.32

V 3.2 3.2 17 1.40

From tables of Thoman, et al

.

P [ m(BLU)< L] = 1-a m

91
FIGURES 9 and 10

The cumulative failure probability as a function of applied stress.

Experimental data (•) and theoretical calculation ( —) assuming a Weibull

distribution.

92
o

CUMULATIVE FAILURE PROBABILITY Flsl

93

FIGURE 9
CUMULATIVE FAILURE PROBABILITY FIs]

io V 05 03 o

FIGURE

10
Figure Tl. Distribution of diametral tensile strength for 2 mm x 3 mm diameter specimens. The curve is for the Wei bull distribution

with parameters shown.

9.5
for

standard

size

specimens

with

curves

calculated

from

the

distribution

for

small

specimens
0.00 Ho.eo i50.ee ibO .

1jO

FIGURE! 3 Distributions of Diametral Tensile Strength fitted to compound

Wei bull distribution for Adaptic specimens after soaking

in Heptane, Ethanol, and water for two weeks

9 7
FIGURE 14 10th an 90th Percentile points for estimates <m>for samples

of size N taken from a Wei bull distribution with exponent m.

98
FIGURE 15 10th a-nd 90th Percentile points for estimates <cr 0

> for samples of -size N- taken from Weibull distributions

with exponent-^ and position parameter cr 0 .

I

I

t

(

t

!

t

i

i

i

I

i

I

ir

K

r

)

i

i

f

Itt

i

i

f

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i

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j

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99

NBS-114A irev. 2 -ac) U.S. DEPT. OF COMM. 1. PUBLICATION OR 2. Performing Organ. Report No. 3. Publication Date BIBLIOGRAPHIC DATA

REPORT NO. SHEET (See instructions) March 1987 NBSIR/87-3539

4. TITLE AND SUBTITLE

Properties and Interactions of Oral Structures and Restorative Materials

5. AUTHOR(S)

John A. Tesk, J. Antonucci , G. Brauer, J. McKinney, R. Penn, J.Stansbury, W.de Rijk _—S.

Ven z, H .—

I

l z uka , S . Lee and K . Asaoka

6. PERFORMING ORGANIZATION (If joint or other than NBS. see instructions)

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No.

8 . Type of Report & Period Covered

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State. ZIP)

National Institute of Genital Research,

NIH, DHHS , Bethesda , MD 20205

10. SUPPLEMENTARY NOTES

J Document describes a computer program; SF-185, FlPS Software Summary, is attached.

1 n \ ..:e research program described herein is designed to achieve a number of

objectives leading to improved dental restorative materials, techniques and

applications of dental materials science for improved dental health care m

general. Some of the research in dental composites is directed toward

developing generic polymer science potentially useful for composite

applications, e.g., durable resin matrices and stronger more durable coupling

between fillers and resins. Improved reinforcement is sought by defining the

typu, ana percentages of fillers which will result in improved performance of

composites. Methods for reducing polymerization shrinkage and attendant stress

marginal leakage are also explored. Cements are investigated and basic

formulations developed for lower solubility, h

strength, greater toughness and adhesion to va and dentin. Analysis techniques include IR

analysis, mechanical tas

directed at elucidating

cental composites and restoratives

ar= pursued as well as bv ide.ntifi

reading to failure, veibuii statistical anal

:mc

n e _

'

her biocompatibility , higher

various substrates including enamel

spectroscopy, chromatography, x-ray

a tome try. Another major effort is

a wear and degradation of

. ^ i

.me roveo. correlations

:cmpcsites wi~h labor:

diiU ^ _ ^ unc a mentals involved in wear and g Wear and hardness measurement techniques

cation of the origins and sources of flaws

expected to provide useful —* ui. ve is to investigate

st ween clinical results of wear and failure cf

cry test data via time-tc-f ailure analysis. Metrology

porcelainicn of dental casting

and analysis constitutes tne under ivmg theme of investigations in r o metai systems, casting cf dental alleys and the expan.cinves fment s

.

13. AVAILABILITY

Unl i mi ted ^X~ For Official Distribution. Do Not Release to NTIS r Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. ~ 20402.

] Order From National Technical Information Service (NTIS), Springfield, VA. 22161

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PRINTED PAGES

15. Price