Properties and Interactions of

Ora! Structures and Restorative

Materials

J. Tesk, J. Antonucci, G. Brauer, J. McKinney, R. Penn, J. Stansbury, W. de Rijk, S. Venz, 0. Okuno and H. lizuka

I

I

|

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*

U S. DEPARTMENT OF COMMERCE

Nationai Bureau of Standards

institute for Materials Science and Engineering . Polymers Division

Dental and Medicai Materials

Gaithersburg, MD 20399

Annual Report for Period

Gctober 1, 1934 to September 30. 1985

Issued February 1936

Interagency Agreement

Y01 -DE30001

Preoared for National Institute of Dental Research

Sethesda. MD 20205

NBSIR 86-3320

PROPERTIES AND INTERACTIONS OF

ORAL STRUCTURES AND RESTORATIVE

MATERIALS

J. Tesk, J. Antonucci, G. Brauer, J. McKinney, R. Penn, J. Stansbury, W. de Rijk, S. Venz, 0. Okuno and H. lizuka

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, 1984 to September 30, 1985

Issued February 1986

Interagency Agreement

Y01 -DE30001

Certain commercial materials and equipment are identified

in this report to specify the experimental procedure.

In no instance does such identification imply recommendation

or endorsement by the National Bureau of Standards or that the materials and equipment identified are necessarily

the best available for the purpose.

Prepared for National Institute of Dental Research

Bethesda, MD 20205

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

NATIONAL BUREAU OF STANDARDS, Ernest Ambler. Director

CONTENTS

Page

ABSTRACT i

FY 85 SIGNIFICANT ACCOMPLISHMENTS ii

STAFF BIOGRAPHICAL SKETCH iii

INTRODUCTION iv

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

Antonucci, Venz, and Iizuka)

Section A through C 9 Brauer

A. High-strength Eugenol-^free Adhesive Cements

and Restoratives 1

B. Changes in Esthetic Properties of Dental

Resins on Aging 5

C. Study of Adhesion and Adhesion Promoting

Agents to Dentin 6

References 8

Publications 10

Patents 10

Manuscript Accepted for Publication 10

Manuscripts Under Review 10

Invited Talks 10

Contributed Talks 10

Section D 4 Stansbury

D. Monomers Which Polymerize with Expansion 11

References 14

Patents 14

Manuscripts Under Review 14

Contributed Talks 14
Page

PART III 4 DENTAL ALLOYS, CERAMICS, METROLOGY AND ANALYSIS (Tesk,

de Rijk, Penn and Asaoka)

General Overview 47

A. Porcelain-JAlloy Compatibility (Thermomechanical Stress) 47

B. Porcelain^Alloy Compatibility (Bonded

System Strength) 49

C. Castability (Filling of a Mold with Cast

Dental Alloy 51

D. Castability (Accuracy of Fit of Dental Castings) ... 55

E. Solderability 56

F. Metrology and Analysis: Measurements for

Characterization of Dental Materials 56

References ’ 60

Publications 61

Manuscripts in Review or Accepted for

Publication 62

Invited Talks 62

Contributed Talks 63
Page

Section E 4 Antonucci

E. Improvement of Dental Composites, Sealant

Cement and Adhesive Materials, Antonucci et al . . . . 15

I. Improvement of Dental Resin Systems for

Composites and Sealants 15

II. Improvement of Dental Cements 19

III. Development of Improved Interfacial Bonding

Systems and Fillers for Composites and Cements. . 21

References 35

Manuscripts Accepted for Publication 38

Manuscripts Under Review 38

Invited Talks 38

Contributed Talks 39

PART II - WEAR AND DAMAGE ASSESSMENT OF RESTORATIONS (McKinney,

Antonucci, Penn, de Rijk and Venz)

General Overview 40

A. Wear and Durability Assessment of Composite

Restoratives 40

B. Glassy-Transition Temperature (T

g

) of Matrix

Polymers 43

References 45

Publications 46

Manuscripts Accepted for Publication 46

Manuscripts Under Review 46

Invited Talks 46

Contributed Talks 46

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 systems potentially applicable to other composite

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

between fillers and resins and improved reinforcement by defining the

types, compositions 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 by wear and hardness measurement techniques, 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 of clinical results on wear and failure of composites

with laboratory test data via a time to failure analysis. Metrology and

analysis constitutes the underlying theme of investigation into

porcelain-metal system, casting of dental alloys and expansion of 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 85 SIGNIFICANT ACCOMPLISHMENTS

Tough, deformable dental-cement formulations which expand slightly on setting have been developed.

Prepolymer resins for dental composites which reduce polymerization

shrinkage and show promise for higher iji vivo durability were also

developed.

Monomers which expand during free-radical polymerization were synthesized.

Monomers with the potential to render dental resins radiopaque were also synthesized.

A dental composite evaluated by diametral tensile testing was shown

to undergo surface induced failure rather than internal-flaw induced

fracture.

Dental composite restoratives were found more prone to color changes

on aging than denture base polymers or resin based synthetic teeth.

Several cements that exhibit significant adhesion to stainless steel,

porcelain and composites were developed.

-Composite formulations with * improved resistance to oral food

simulating liquids were developed and found to have acceptable

properties.

Glass ionomer cements were found to undergo catastrophic failure

under all conditions of wear evaluation.

.preconditioning in air or lactic acid produced the worst results.

An experimental composite formulation was found to have its wear unaffected by preconditioning in oral food-simulating liquids.

The effects of investment variables (batch, brand) on a castability

value for dental casting alloy were demonstrated.

A mercury dilatometer was developed for measuring polymerization

shrinkage or expansion of dental resins, composites and cements.

The internal setting expansion of phosphate bonded dental investments

was confirmed at low values, - 0.1 by refined experiments using

strain gauges.

The diametral tensile test was shown to be a viable method for

evaluating tensile strength of dental composites and cements.
DENTAL

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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

.

Part 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 porcelain-fused-to-metal studies. Special emphasis is being placed on measurement techniques and flaw analysis.

i v
I. COMPOSITES, CEMENTS AND ADHESION

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

PROGRESS REPORT

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 of permanent protheses or as intermediate restoratives.

Non-eugenol containing cements based on vanillate esters,

o-ethoxybenzoic acid (EBA) and zinc oxide, have been developed in this

laboratory. [1] 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) non- inhibit ion of free radical polymerization; thus can

be used in conjunction with composite filling materials, (4)

compatibility with acrylic monomers which permits the formulation of

hybrid composite-cements and (5) strong adhesion, even on prolonged

water exposure, to non-precious metals, porcelain and composites.

Objective

The objective of this study was to evaluate these cements for various

dental applications and to further improve desirable properties. To

achieve this objective the following tasks were undertaken: (1)

synthesis and evaluation of divanillates and polymerizable vanillates

such as methacryloxyethyl vanillate and addition to these compounds of

hexyl vanillate-ethoxybenzoic acid (HV-EBA) 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

car ies-reducing syringic esters and evaluation of properties of the

resulting cements; (5) modif ication of these cements by addition of

small concentrations of additives such as acids, metals or fluorides

to improve their properties (6) furnishing of assistance and guidance

to conduct investigations of the biocompatibility and toxicity of the

cement and its ingredients and collaboration in studies of pulp

irritation and in clinical studies at various dental research centers.
Accomplishments

Phase I - (la) Synthesis of Divanillates and Polymerizable Vanillates as Ingredients of Dental Cements.

To achieve higher strength and lower solubility, a series of

esters of vanillic acid as well as compounds with

multifunctional groups such as decamethylene or hexamethylene divanillate or methacryloxyethyl vanillate

that react with metal oxides to give chain-extended products

have been synthesized in the previous year. These compounds

were incorporated successfully into dental cements and

resulted in materials with improved properties. A manuscript describing these investigations in detail has

been published in the Journal of Dental Research and in the

Journal of Biomedical Materials Research. [2]

(lb) Adhesion of Cements to Various Substrates.

It was demonstrated previously that these cements have

significantly stronger adhesion than ZOE to all substrates

including dentin and enamel. Recent results show that the

hexyl vanillate-EBA cements adhere especially well to

non-precious metals, porcelain and composites. The joined

specimens break cohesively close to or above the tensile

strength of the cement. With acid-modified cements bond

strengths as high as 19.9 MPa (2880 psi) have been obtained.

Strength of the porcelain-to-porcelain, porcelain-tostainles3 steel and porcelain-to-composite bonds after 24

hour storage in 37 °C water were 13.9 MPa (2020 psi), 6.9

MPa (1000 psi) and 4.9 MPa (712 psi) respectively.

(lc) Formulation of Intermediate Restorative Materials.

n-Hexyl vanillate-EBA-ZnO cements are compatible with

acrylic monomers (dicyclopentenyloxyethyl methacrylate,

cyclohexyl methacrylate). Such solutions mixed with powder,

made up from silanized glass reinforcing agent and zinc

oxide and containing suitable peroxide-amine

initiator-accelerator systems, have good working properties

and harden in a few minutes. The cured materials have both

compressive and tensile strengths one and a half to three

times that of eugenol-based intermediate restorati ves . These

cement-composites adhere strongly to composites,

non-precious metals or porcelain (maximum bond strength 15.6

MPa) . Rupture of the bond occurs as the result of cohesive

failure. Because of their high strength and excellent

adhesion, the cements, subject to their biocompatibility

with dental tissues, show great promise as intermediate

restorative resins and in the repair of fractured porcelain

or porcelain to metal crown or bridges. Details of this

investigation have been published. [33

2
Phase II -

(l d) Synthesis and Evaluation of Cements with Syringic Acid Ester

Ingredients.

Evaluation of mixes containing these potentially

oaries-redueing esters, n-hexyl vanillate, EBA and zinc

oxide powder are rapid setting, water insoluble, possess

high strength. [4,5] The syringate cements, compared with

the commonly used ZOE materials, have improved compressive

and tensile strength, lower water solubility, do not inhibit

polymerization, and are compatible with acrylic monomers.

They bond significantly to resins, composites, and

non-precious metals.

The cements, because of the syringate ingredient, may

possess caries-reducing properties. Thus, perhaps in

conjunction with fluoride additives, they would be useful as luting agents, insulating bases, pulp capping agents, root

canal sealers, soft tissue packs, or intermediate

restoratives.

(le) Modification of Cements by Incorporation of Additives.

Addition of small concentrations of acid, metals or fluorides to vanillate or syringate dental cements was studied to improve their physical properties and

anticar iogenic behavior. [6] Incorporation of acids into

cement formulations lowers their' setting time. Coating a portion of the zinc oxide powder ingredient with propionic

acid offers a convenient way of adjusting the curing rate

most suitable for clinical applications. The resulting

cements are nonbrittle, have high strength, low solubility

and bond strongly to non-precious metals, porcelain or composites. Cements with zinc undecylate are flexible and

may be useful as soft tissue packs. Metallic powders do not

act as reinforcing agents for these cements.

Hexyl vanillate or ethylhexyl syringate cements can be

prepared by adding 0.1 percent to 1 percent fluoride salts

such as NaF, ZrF^, ZnF 2 or dimethylaminoethyl methacrylate

hydrofluor ide to the powder ingredient. Rate of fluoride

released is dependent on the solubility of the fluoride in

water and decreases rapidly

exposure to the liquid.

within the first few days after

Phase III Study

Usefulness

of Biocorapatibility

,

Toxicity and Clinical

(3a) Synthesis

Studies.

of Materials for Pre-clinical and Clinical

Vanillate and syringate esters synthesized in this

laboratory have been made available to many researchers on request. Hexyl vanillate is now commercially available from

two manufacturers of specialty chemicals.

3
(3b) Toxicity and Biological Evaluation of HV-EBA-ZnO Cements.

The biological safety evaluation of the hexyl vanillate

(HV)-EBA-ZnO cements has been completed. [7] Most

ingredients of the cement gave a negative hemolysis test.

o-Ethoxybenzoic acid, however, gave a positive result for

rabbit red blood cell hemolysis. Oral LD^q in mice varied

from 0.70 g/kg for o-ethoxybenzoic acid to over 1 .00g/kg for

n-hexyl vanillate and ZnO-A^O^-hydrogenated rosin powder.

The cloning efficiency test for EBA and the cement powder

were negative at all concentrations whereas concentration

above 25ug/ml HV resulted in a- positive test. Ames

mutagenicity tests for EBA, HV, Zn0-Al 20o hydrogenated rosin

powder and cement extract using salmonella strains TA 97, TA

98, TA 100 and TA 102 were negative. Thus, these results and

those obtained previously [ 8 ] indicate that none of the

ingredients of HV-EBA cements is toxic or mutagenic.

(3c) Biocompatibility of Syringate-Vanillate-EBA-ZnO Cements.

Studies by Dr. C. Siew of the American Dental Association

Health Foundation evaluating the biocompatibility of the

ingredients of ethylhexyl syr ingate-HV-EBA-ZnO cements are nearing completion.

(3d) Application for Periodontal Dressings

Studies by Rubinoff and Greener [ 9 ] using HV-EBA-ZnO

formulations containing 12.6 percent Crisco as periodontal

dressings showed that these compositions had physical

properties equal to or superior to those of commercial

dressings. Their ease of mixing and clean handling

properties together with their non-eugenol composition

indicate that these materials show promise as periodontal

dressings.

(3e) Application as Endodontic Sealers

Endodontic sealers prepared from HV-EBA-ZnO and 10 percent

BaSOjj sealed significantly better at room temperature or 37

°C than eugenol containing controls. Implantation studies

in rabbits showed that the biocorapatibility of this sealer

was equivalent to that of Grossman's cement. [10]

Conclusion

Based on the results of the biocorapatibility tests it was concluded that clinical evaluation of the HV-EBA cement could

proceed. The cement is now being made available to interested

parties for clinical studies.
B. Changes in Esthetic Properties of Dental Resina on Aging .

PROGRESS REPORT

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 esthetically

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 its 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.

Accompl i shment

We found that dental composites are more susceptable to undergo color

changes on aging (especially on exposure to radiation) than denture

base resins or plastic teeth. Therefore, a series of composites of

the chemically cured (traditional, hybrid and micro-filled), light

cured (traditional and micro-filled) and traditional (combined light

and chemical cured) type were exposed to the Xenon and RS lamp for

time periods ranging from six hours to seven days. [11] Irradiation

of the materials by the RS lamp and in air produced more discoloration

than exposure to the Xenon lamp in water. Visible light cured

materials were more color stable than chemical cured ones. Light

shades were more susceptible to color changes than dark shades of the same brand. Exposure of composites to 60 °C in the dark lead to much

more rapid discoloration for materials stored in water than in air.

Thus, most chemically activated composites when stored in water showed

distinct color changes after one month whereas those stored in air had

similar discoloration after exposure for three or more months.

Clinical investigations to confirm what laboratory conditions for

color stability tests best correlate with the color changes of

restoratives in the mouth are available at present only for the

chemically cured materials.

5
A liquid chromatograph has been 3et up to analyze the ingredients of

the composites studied in the above investigation. Using a C— 1

capped-silica column elution peaks for various peroxides, monomers,

and amine accelerators have been established. Ingredients of one paste have been analyzed.

C. Study of Adhesion and Adhesion Promoting Agents to Dentin .

PROGRESS REPORT

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 micro-organisms 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 is contraindicated for

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

to dentin [ 12-15 ] 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

[16] and to dentin with tri-n-butylborane oxide as initiator. [17,18]

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. [19] A mixture of a phosphorus ester of

BIS-GMA and diluent monomer polymerizable by peroxide, tertiary amine

and sulfinic acid salt has been introduced commercially as a dentin-composite bonding agent. [20] Monomers with hydrophobic and

hydrophilic moieties such as 4-methacryloxyethyl trimellitic anhydride

(4.-META) and the diadduct of hydroxyethyl methacrylate and

pyromellitic anhydride (4-PMDM) bond dentin to acrylic resins. [21,22]

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 4-PMDM in acetone.

[ 22 ] Another good bonding agent to dentin is the mixture of

2-hydroxyethyl methacrylate and glutaraldehyde . [23~25]

6
Objective

The objective of this study has been to synthesize specific monomers

or oligomers such as allyl 2-cyanoacrylate or oligomers of

2-isocyanatoethyl methacrylate and to prepare suitable formulations

using these ingredients which may bond to dentin in an aqueous

environment.

Accomplishments

Phase I -Synthesize and evaluate adhesive properties of oligomers of

2-isocyanatoethyl methacrylate to dental tissues.

A copolymer was synthesized by the reaction of n-butyl

methacrylate (35 wt percent), ethyl acrylate (35 wt percent)

and 2-isocyanatoethyl methacrylate (30 wt percent) in

ethoxyethyl acetate with azoisobutyronitrile as initiator.

The vitreous colorless solid containing pendant isocyanate

groups as established from infra-red spectra will be reacted

with mineralized tissue such as bone or dentin to determine

if grafting of this polymer and collagen containing surfaces

takes place.

To this prepolymer methacrylate side chains could be grafted

through the isocyanate groups. The prepolymer dissolved in

2-ethoxyethyl acetate was reacted with 2-hydroxyethyl

methacrylate in a nitrogen atmosphere and in the presence of

dibutyl tin dilaurate. A hard solid slightly tan polymer

was recovered. Infra red spectra indicated that thi3

material contained urethane and methacrylate groups, but few

unreacted isocyanate groups.

Phase II - If appropriate, proceed to arrange pre-clinical trials.

This study has not progressed to the state where preclinical

trials are warranted.

7
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, Dec. 7, 1982.

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

Vanillates as ingredients of Dental Cements, J. Biomed. Mat. Res. 19,

(1985).

[3] Brauer, G.M. and Stansbury, J.W. Intermediate Restoratives from

n-Hexyl Vanillate-EBA-ZnO-Glass Composites. J. Dent. Res. 6^,

1 315-1 320 (1984).

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

Esters-o-Ethoxybenzoic Acid and Zinc Oxide. J. Dent. Res. 6j3, 137-140

(1984).

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

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

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

Syringate Cements Containing Various Fluorides. IADR Prog, and Abst.

64, No. 314 (1985).

[7] Siew, S., Gruninger, S. , 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. 6_4

,

No. 1473 (1985).

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

Prog, and Abst. 63, No. 1278 (1984).

[9] Rubinoff, C.H. and Greener, E.H. Physical Properties of an experimental Dressing Material. Dent. Mat. J_, 3-6 ( 1985).

[10] 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. 64, No. 77 (1985).

[11] Brauer, G.M. and Stansbury, J.W. . Color Changes of Composites on Exposure to Various Energy Sources. IADR Prog, and Abst. 6_4, 310

(1984).

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

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

Printing Office, Washington, DC 1966.

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

Marcel DeKker, NY, NY, 1972, p. 731-800.

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

8
[15] 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 .

[16] Brauer, G.M., Termini, D.J. and Levy, S.M. J. Dent. Res., 56,

646-659 (1977).

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

[18] Miura, F., Nahagawa, K. and Masuhara, E. Am. J. Orthod., 59, 35

( 1 971 ) .

-

[19] Brauer, G.M., Jackson, J.A. and Termini, D.J. J. Dent. Res., ^8,

1900-1907 ( 1979)

[20] 3M Dental Products Department, Pamphlet, Scotchbond Dental Adhesive

System (1982).

[21] U.S. Patent, 4,148,988 (April 10, 1979), E. Masuhara, N. Nakabayashi

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

[22] Bowen, R.L., Coble, E.N. and Rapson, J.E. J. Dent. Res., 6J_,

1070-1076 (1982).

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

Restorative Resins Mediated by Mixtures of HEMA and Gentaraldehyde . J.

Dent. Res. 63 , 1087-1089 (1984).

[24] Dentin-Polymer Bond in Resin Fillings Tested iri vitro by Thermo and

Load-cycling, J. Dent. Res. _64, 1 44-1 46 ( 1985).

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

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

9
Publications

1 . Intermediate Restoratives from n-Hexyl Vanillate-EBA-ZnO-Glass

Composities, G.M. Brauer and J.W. Stansbury, J. Dent. Res. 63,

1315-1320 (1984).' ' -

2. Divanillates and Polymerizable Vanillates as Ingredients of Dental

Cements, J.W. Stansbury and G.M. Brauer, J. Biomed. Mat. Res. J_9,

715-725, (1985).

Patents

1. Biocompatible Cemetitious Compositions, G.M. Brauer and J.W.

Stansbury, U.S. Patent 4,486,179, Dec. 4, 1 984

Manuscript accepted for publication

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

Encyclopaedia of Polymer Science and Engineering, Vol. V.,

Wiley-Interscience, NY, NY, (1985) (in press).

Manuscripts under review

1. The Effect of Inhibitors, Accelerators, Cross-linking Agents and

Monomers on the Properties of Bone Cement, G.M. Brauer, D.R.

Steinberger, and J.W. Stansbury (submitted for publication to J.

Biomed. Mat. Res.).

2. Modification of Cements Containing Vanillate or Syringate Esters, G.M.

Brauer, J.W. Stansbury and D. Flowers. (Submitted for publication

-Dent. Mat.)'

Invited talks

"New Adhesive Dental Cements from Hexyl Vanillate-EBA-Zinc Oxide. Academy

of Dental Materials, Feb. 1985.

Contributed talk3

"Properties of Vanillate and Syringate Cements Containing Various

Fluorides", J.W. Stansbury and G.M. Brauer. IADR/AADR meeting 1985.

"Color Changes of Composites on Exposure to Various Energy Sources", G.M.

Brauer and J.W. Stansbury, IADR/AADR meeting 1985.

"Biological Safety Evaluation of a Newly Developed High Strength, Acrylic

Resin Compatible Adhesive Cement", C. Siew, S. Gruninger, R. Hsu, J.M.

Brauer, J.A. Tesk, IADR/AADR meeting 1985.

"Modification of Cements Containing Vanillate or Syringate Esters. D. Flowers and G.M. Brauer, Chemical Society of Washington, April 1985.

10
Monomers Which Polymerize with Expansion

Overview

A major deficiency inherent in all commercial monomers utilized in

dental adhesives and composites is the shrinkage that accompanies

their polymerization. The stresses resulting from this contraction of

the resin often are manifested as microcracks, marginal gaps or by

debonding at the filler particle interface in composites. Efforts to

minimize the degree of polymerization shrinkage have included the use

of hydrophilic monomers to promote a compensatory hygroscopic

expansion by water sorption [1], reduction in the proportion of

diluent monomer used [2] and the utilization of prepolymers. [33 In a different approach, which directly addresses the problem of

polymerization shrinkage, our effort has been aimed at preparing novel

spiro orthocarbonate monomers which will expand upon polymerization to

counter the contraction of conventional monomers.

PROGRESS REPORT

Phase I - Synthesis

This investigation required the synthesis of new monomers capable

of free-radical polymerization with an accompanying expansion in

volume. Further, these monomers should contain substituents which

provide for polymers with glass transition temperatures that are comparable to commercial materials. A previously reported method

for preparing unsubstituted, symmetrical spiro orthocarbonates

[4] was not applicable for the synthesis of substituted,

asymmetric 3piro monomers. Therefore, a new procedure was developed in which a high energy, cyclic thionocarbonate was utilized as an intermediate in the preparation of spiro

orthocarbonates. This was accomplished by the reaction of a 1 , 3-diol with thiophosgene in the presence of dimethylaminopyr idine

( DMAP ) at 0 °C. (Figure 1) The synthesis of

5,5-dimethyl-1 ,3~dioxa-2-cyclohexanethione (_1) was the first time

that any

Figure 1
six~raembered thionocarbonate had been isolated. This reactive

intermediate yielded the new monomer, 3. 3“dimethyl-9-methylene1 .5 ,7 , 1

1 -tetraoxaspiro [5.5] undecane ( 2 ) at room temperature,

whereas spiro orthocarbonates synthesized by prior techniques

required prolonged heating at >100 °C. Other monomers (Table 1)

with higher degrees of substitution were prepared by this same technique. It is apparent that the substituents must be chosen

to maximize the asymmetry of the compound if highly substituted

monomers with low melting points are to be obtained.

no. 2 no. 3 no. 4 no. 5 no. 6

Compound

Spiro orthocarbonate

monomer mp (bp)

2 o:> 34°C (76°C/2mm)

3 DQO ( 1 02°C/0 . 5mm)

4 >bo 28°C (80°C/3mm)

5 OQO 52°C (125°C/0.3mm)

6 XX? (75°C/0.3mm)

3,3-dimethyl-9-methylene-1 ,5 ,7,

1 -tetraoxaspiro [5.5] undecane

diethyl substituted

dimethyl-isopropyl substituted

cyclohexene substituted

3 , 3~dimethyl-9-methylene-1 ,5 ,7 , 1 2-tetraoxaspiro [5.6] dodecane

Table I

12
While thionocarbonates were originally obtained in yields of 50

percent or less, the synthetic procedure has been refined to

achieve greatly improved yields. To demonstrate this more

efficient technique, the yield of thionocarbonate 1 was increased

from 50 to 96 percent and the highly substituted '7 was prepared

in 82 percent yield compared to a 5 percent yield in the initial

synthesis.

A spiro monomer containing a seven-membered ring (j>) has been

synthesized. This liquid monomer is expected to ring open more

readily due to additional strain and provide a greater degree of

expansion than monomers based on six-membered rings.

The preparation of nitrogen substituted spiro orthocarbonates

which should give rise to stiff urethane linkages in the ring

opened polymers has been initiated. A cyclic thiourethane (_8)

obtained from t_-butyl aminoethanol has been synthesized. An

attempt to produce the nitrogen containing monomer (_9) was unsuccessfully carried out. The steric hinderance of the t_-butyl

group on nitrogen is likely to blame for the failure to form the

spiro linkage. The cyclic thioamide from methylaminoethanol will

be prepared and subjected to this same reaction.

Figure 3

Phase II and III - Formulation and Evaluation

While these spiro monomers are sluggish to homopolymer ize , they

readily form copolymers with the more reactive, acrylate monomers

used in dentistry. In initial formulation work it was found that

TEGDMA could be replaced entirely with the liquid spiro monomer

(_3) which served as diluent monomer for the bis-GMA. Upon

curing, this composite resin exhibited a DTS value which was only

about 5 percent less than the control while the shrinkage

evaluation showed a slight volume expansion occurring after the

initial polymerization shrinkage.

13
References

[1] Derman, K. , Rupp, N.W. and Brauer, G.M. Effect of Hyrophilic Diluents

on the Properties of Cured Composites, J. Dent. Res. 61 1250-1254,

1982.

[2] Brauer, G.M. , Dulik, D.M. , Hughes, H.N., Derman, K. and Rupp, N.W.

Marginal Adaptation of BIS-GMA-based Composites Containing Various

Diluents. J. Dent. Res. _60 1966-1971 , 1981 .

[3] Antonucci, J.M. New Monomers for Use in Dentistry, Biomedical and

Dental Applications of Polymers. Plenum Publishing Corp. 357-371,

1981

[4] Bailey, W.J. and Endo, T. Synthesis of Monomers that Expand on Polymerization. J. Polym. Sci., Polym. Chem. Ed. 14 1735-1741, 1976.

Publications

1 . Intermediate Restoratives from n-Hexyl Vanillate-EBA-ZnO-Glass

Composities, G.M. Brauer and J.W. Stansbury, J. Dent. Res. 6^,

1 315-1 320 ( 1984).

2. Divanillates and Polymerizable Vanillates as Ingredients of Dental

Cements, J.W. Stansbury and G.M. Brauer, J. Biomed. Mat. Res. J_9,

715-725, (.1985).

Patents

1. Biocompatible Cemetitious Compositions, G.M. Brauer and J.W.

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

Manuscripts under review

1. The Effect of Inhibitors, Accelerators, Cross-linking Agents and

Monomers on the Properties of Bone Cement, G.M. Brauer, D.R.

Steinberger, and J.W. Stansbury (submitted for publication to J. Biomed. Mat. Res.).

2. Modification of Cements Containing Vanillate or Syringate Esters, G.M.

Brauer, J.W. Stansbury and D. Flowers. (Submitted for publication

-Dent. Mat.)

Contributed talks

’’Properties of Vanillate and Syringate Cements Containing Various

Fluorides", J.W. Stansbury and G.M. Brauer. IADR/AADR meeting 1985.

"Color Changes of Composites on Exposure to Various Energy Sources", G.M.

Brauer and J.W. Stansbury, IADR/AADR meeting 1985.
E. Improvement of Dental Composites, Sealant Cement and Adhesive

Materials

This part of the annual report is divided into four distinct sections:

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 Inter facial Bonding Systems and Fillers for

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

(Synthesis, Formulation and Evaluation)

IV. Preclinical and Clinical Testing.

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

Overview (composites)

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 dental

sealants [ 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

constitute the dispersed phase, (3) an inter facial 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 ionoraer 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 [7-1 6]. Efforts to enhance

15
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

solubility parameter, residual vinyl unsaturation and polymerization

shrinkage of the resin phase, and the development of more effective

inter facial bonding phases.

Dental sealants have similar compositions and chemistry but are unfilled or only lightly filled and usually contain a higher

proportion of diluent raonomer(s).

Objective

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

composite, sealant, cement and adhesive materials through the use of

hydrophobic resins.

Introduction

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 stress-bear ing application

[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

degradative ' 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 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 and solubility parameters to

resist the detrimental effects of the oral environment [24,25,30,31].

The second approach, which also may encompass 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 [27,28,32]. 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

initiator systems for ambient polymerizations of dental resins in 1 more uniform fashion [27].

16
PROGRESS REPORT

Phase I - Synthesis, Formulation and Evaluation of Resin Systems.

(1) Synthesis and characterization of the monomers, PFUMA,

BIS-GMA/ 2-1 EM , BIS-C2-1A/MPDMS were achieved as outlined

in Figures' 1 -3.

a. Synthesis of a Polyfluor inated Prepolymer

Multi-functional Urethane Methacrylate (PFUMA).

Urethane methacrylate resins yield composites of

high strength but with water sorption (WS) similar

to BIS-GMA-composites. The rationale of this study

was to prepare a more hydrophobic urethane

methacrylate resin. The polyfluorinated oligomeric

polyol (PFP) used' in the synthesis of PFMA was converted to a multifunctional urethane

methacrylate using the difunctional monomer

isocyanatoethyl methacrylate (IEM) as outlined in

Figure 1 . IEM, via its NCO group, reacts with the

pendant OH groups of PFP yielding the

polyfluorinated prepolymer monomer, PFUMA, which

contains pendant urethane-ethyl methacrylate

groups. PFUMA is a pale yellow liquid of greater

viscosity and cohesive energy density than the

previously synthesized PFMA (Figure 4). PFUMA

also has a higher refractive index than PFMA

(1.4347 vs 1,4197) which may make it more optically compatible with radiopaque glass fillers

than PFMA. Structural confirmation by elemental,

infrared and NMR analyses has been obtained. As was the case wth PFMA, PFUMA is miscible with a variety of diluent monomers (Figure 5). A

preliminary study of several PFUMA based

composites indicate that they are somewhat

stronger (e.g. DTS=47 MPa) than similar PFMA based

composites and have WS values almost as low. They

have polymerization shrinkages that are significantly lower than several commercial

composites (see Table 1). Detailed results of

this study were presented at the 1985 AADR/IADR

Meeting and at the Second International Conference

on Polymers in Medicine in Capri, Italy, June,

1985. A manuscript has been prepared for

publication.

b. Dental Resins for Increased Degree of

Polymerization and Crosslink Density.

Synthesis of a Diurethane tetramethacrylate

(BIS-GMA/2-IEM) . - The diadduct of BIS-GMA and IEM was prepared as shown which further shows the

utility of IEM as a reagent for urethane

methacrylate formation. (Fig. 2) BIS-GMA/2-IEM is

17
an almost colorless liquid somewhat less viscous

than BIS-GMA despite its greater bulk (molecular

weight = 822). Composites based on this

tetrafunctional, bulky monomer have acceptable

mechanical strength (e.g. DTS = 47 MPa). Other

properties (e.g. degree of cure, polymerization

shrinkage compatibility with other base monomers,

etc.) are under study.

Synthesis of a Disiloxane Tetramethacrylate. Again

from BIS-GMA, a unique tetrafunctional vinyl

monomer of greater flexibility was prepared using

3-methacryloxpropyldimethylchlorosilane (MPDMS ) as shown in Fig. 3. BIS-GMA/MPDMS was isolated in

excellent yield as a pale yellow liquid with a viscosity significantly less than that of BIS-GMA

despite its much greater bulk (molecular weight =* 880). Infrared analysis indicated that virtually

all the OH absorption of BIS-GMA had disappeared.

The resin polymerizes by the usual free radical

methods. A preliminary investigation of a composite prepared with this unique monomer alone

revealed that an extremely high powder /liquid

ratio of 6 was achievable using a conventional

silanized barium oxide glass. That is, the filler

content of these composites was 86$ by weight

(-70$ by volume); diametral tensile strength of

visible light cured composites was 42 MPa. Other

properties of this unique resin (especially its

potential use as a low shrinking diluent monomer)

and its composites are under investigation.

(2) Formulation of resins and composites based on the

newly synthesized monomers and PFMA (Figure 4) with

various diluent monomers including the disiloxane

diluent monomer, BIS-MPTMS (Figure 5).

a. Using diluents such as BIS-MPTMS, several visible

light activated PFMA based composites have been

prepared having acceptable mechanical strength and

both low water sorption and polymerization

shrinkage.

b. Formulation and Evaluation of Composites Utilizing

a Disiloxane Diluent Monomer (BIS-MPTMS).

This task was directed at assessing the effect of

bis-( methacryloxypropy 1) tetramethyldisi loxane , BIS-MPTMS, as a diluent monomer on the properties

of dental composites based on 3IS-GMA, BIS-IPMA,

2 , 2-[p-( me thacry loxy isopr opoxy ) phenyl ] propane , and other base monomers (Table 2). The details of

this study were presented at the 1985 IADR/AADR

meeting and a manuscript has been prepared for

publication [25]. The salient point is the

18
maintenance of the good mechanical properties of

the base resins even though significant amounts of

the very flexible disiloxane diluent are used

(Table 3). Water uptake for these siloxane

composites' is generally less than for similar

composites using TEGDMA as a diluent (Table 4).

The use of the less viscous, highly flexible

BIS-MPTMS in place of TEGDMA also permits higher

filler loadings than feasible with BIS-GMA which

also contributes to the lower water sorption

values. This unique diluent monomer is also

compatible with some hydrocarbon urethane

methacrylate monomers, PFMA and PFUMA. Several of

these siloxane-containing composites exhibited

significantly improved OER’s [25].

c. The Effect of Diluent Types and Concentrations on Polymerization Conversion and Shrinkage

The results of this study are summarized in Figure

6. For pure BIS-GMA resin, the polymerization

shrinkage (PS) is low but the degree of conversion

(DC) is also low (about 33 percent); i.e., as the

diluent concentration increases both DC and PS

increase. With the more bulky type of diluent

monomers (e.g., BIS-MPTMS and EPBADMA , Figure 5)

the increase in PS with diluent concentration is

more moderate than that observed with increasing

amounts of TEGDMA. Details of this study were

presented at the 1985 AADR/IADR meeting.

Phase II - Prototype Composite for Clinical Evaluation

A chemically activated, powder /liquid , PFMA composite

formulation using a conventional fused quartz filler has

been delivered to Dr. Joseph Moffa of USAIDR for

evaluation.

II. Improvement of Dental Cements

Overview

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 polyelectroy lte cements (e.g., glass ionomer) and

mineralized tissue also may explain their adhesion to tooth structure

[4].

19
Two types of dental cements can be distinguished depending on their

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

phosphate, polycarboxylate, glass ionomer) and in which water plays a major 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 are needed to achieve clinically acceptable setting

times (e.g., zinc oxide/eugenol-ethoxybenzoic acid, hexyl

vanillate-ethoxybenzoic acid, dimer acid, etc., type cements) and in

the development of their structure.

Objective

To enhance the durability of dental cements by improving their

hydrolytic stability, especially under acidic oral conditions (e.g.,

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 halatopolyraers) , were developed from

the commercially available and hydrocarbon polycarboxylic

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

metallic dimerates and trimerates matrices of these cements are

halatopolyraers, 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

eugenol 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 yet provide an alkaline environment which may promote secondary dentin formation.

They may find utility as Ca(0H) 2 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 [33~35]. 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, September 18, 1985.

PROGRESS REPORT

This particular phase of our general program to develop cements of

improved durability resulted in strong, tough DA/ZnO cements of low

solubility, similar DA/MgO cements, and DA/Ca(0H) 2 cements having

improved dimensional stability, low water solubility, enhanced

mechanical strength and esthetics superior to ZOE cements and, In some formulations, with comparable radiopacity. Strong, esthetic cement'

from DA/Ca(0H) 2 modified with MgO can have various degrees of

radiopacity by use of fillers such as radiopaque glass, titanium >x i le

20
and zirconium compounds. Dilatometric measurements indicate that these

cements generally are low shrinking. In some cases, volumetric

expansion on setting occurs suggesting that these cements have the

potential to reduce microleakage. Details of this study were

presented at the 1985 AADR/IADR meeting.

By proper selection of the base/filler components DA and TA cements

with various degrees of translucency can be prepared. Some of these

cements harmonize well with the appearance of enamel suggesting their

potential for use as an esthetic, intermediate restorative material.

For example, translucent cements resulted from using calcium base

powders (e.g. Ca(0H) 2

) with fillers such as fumed alumina, pyrogenic

silica, tricalcium phosphate (Ca^PO^^), composite vitreous fillers

and various other optically compatible fillers. With magnesium base

powders (e.g. MgO) or mixed Ca(OH) 2 -MgO powders less translucent, but

stronger and less soluble cement3 are formed. Zinc base powders (e.g.

ZnO), as expected, yield opaque cements. The versatile nature of DA

and TA cements suggests a wide variety of dental application. Two

manuscripts have been prepared for publication.

III. Development of Improved Interfacial Bonding Systems and Fillers

' for Composites and Cement3

Overview (filler)

On a weight basis the major component of dental composities 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 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 approximating 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, submicron

fillers such as precipitated or pyrogenic silicas (0 . 1 4-0. 007um)

averaging 0.04 um 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 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/ inorganic, macrofillers

are made from pulverized, prepolymerized composites derived from the

silanized, microfine fillers and the same or similar monomer system.

Composites formulated with these prepolymer ized composite fillers also

are termed microfilled composites.

21
Compared to conventional composites with their larger filler sizes

(0.7. to 100 um, but usually 3-50um) , 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

elastic 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 (and actually improving) other properties. Some

of the newer hybrid composites have a multimodal dispersed phase

consisting of different types, shapes and sizes of fillers.

In addition to silanization, another 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. [36-37] Properly done this

results in a glass filler having superficial surface porosity into

which the resin can 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 conducive to optimal packing

efficiency. New techniques that significantly increase filler

loadings have recently been developed. [38]

Overview (In ter facial Bonding Phase)

Although they are only minor components of resin based dental

restorative materials, interfacial bonding agents exert profound

effect on the durability of these 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 inter facial bonding phase.

Bifunctional coupling agents such as organo functional silanes,

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

adhesion between mineral fillers and organic resin binders.

Alkoxysilances having terminal vinyl groups have been the most widely

used type of coupling agent for dental composites. Initially, i vinyltr ialkoxysilane was used but it was later found that

3-methacryloxypropyltrimethoxysilane was more effective.

Alkoxysilanes can react with surface moisture, usually present it

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 so^

22
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. Organo functional

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 by 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) and

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

Phase II - Development of Improved Interfacial Bonding Phases for

Composites and Cements

Objective 1

Develop improved coupling systems for fillers by integral blending,

dual silanization and other bonding techniques.

PROGRESS REPORT

A study to assess the relative merits of integral blending of silane

coupling agents in composites versus their prior application onto

fillers has been initiated. Preliminary results with A-174 dissolved

in a BIS-GMA resin paste indicate that in situ silanization occurs

over a relatively short period (-2-3 days) and that such cured

composites have about the same DTS values as similar composites

prepared with presilanized fillers. A second study is in progress to

assess the coupling efficacy of other commercially available silane

agents, e.g. 3-N,N-dimethylaminopropytrimethoxysilane , 3-CMAPS,

predicated on its radical-forming reductive interaction with

camphoroquinone (CQ) in visible light activated composites, and

3-mercapto-propytrimethoxysilane (3~MPS) which may bond to the resin

by chain transfer reactions. Preliminary results indicate little, if

any, coupling of phases occurs using 3~DMAPS. Also when dissolved in

the resin phase it is a poor photoreductant ' for CQ. Similarly, only

modest coupling with 3“MPS has been observed as measured by

comparative DTS measurements using unsilanized glass composites as a control. Dual silanization studies are in progress with these and

other types of silane agents.

Objective 2

Formulation of composite or cement systems with various fillers

treated with the best new or binary coupling agents. This work is

deferred until the completion of Part 1 of Phase II.

23
Objective 3

Determination of physical, chemical or mechanical

appropriate. Utilize analytical techniques (e.g.

analysis, etc.) as required to assess the type

silanization. ‘Work on this part also i-S deferred.

properties as HPLC, thermal

and degree of

24
CF.

1 3

C

CF= k®

I

CF.

I

CF.

I -C-XH^^H-^. -OC-CHhCH-CH -C-OCH_-CH-CH -o

ICF.

IOH

CH.C1

2 2

ICF.

I CF.

2

|OH

PFP

0

II CH_=C-C-0-CH_-CH_-N=C=0

2

| 2 2

CH.

I EM

N

n*io

CF

I 3

C—

I CF.

CF.

I

CF.

I

CF. —C-XH^CH-CH_-0C-CH=CH-€H_C-0CH_-CH-CH^-0-

CF. 0

I C=0

I NH

ch2=1

CH

L

i?

c=o

I ?

CH,

CF. CF.

I0

Ic=o

INH

h

CH,

0

I o=c

A=CH

CH.

N

MW = 12,060

%F = 37.8

Figure 1. SYNTHESIS OF PFUMA

25
C=C-C-0-CH-CH-CH-Q-( ()>— C— (()

)-0-CH

-CH-CH

-0-C-C=CH

26

Figure 2

SYNTHESIS

DFBI

S-GMA/2

-IEM
Q

0

HC=C-C-CM>l_-CH--CHo-0-

2 I 2 t 2

CH. i,

'Q-CH_-*CH-CH_-C-C-C=CH.

OH CH.

BIS-GMA

j

H

:

2 CHo-C-C-O-CHpCHpCHp-Si-Cl

II MPDMS [ 0 CH-3

H^CsC-C-O-CH^-CH-CH^-0-

CH. i

tn t x —

m

x

i

cvj X

oOJ X

oCVJ X

o

» 01 u =

I -o

I

CVJ X

o

f’ —c—

I CH,

0

-0-CH -CH-CH -O-C-OCH.

2 t 2 | 2

m t X —

on x

i

CVJ x

oCVJ X

o

cvj X0

1 0

1 0 = -o

1

CVJ X

o

CH.

Figure 3 BIS-GMA/MPDMS

27
SYNTHESIS

OF

POLYMETHACRYLATE

(PFMA)

OICM

LU

I

CM

LU

co o

LU I LL_ LU— LU— LU

CM LU

I LU

II

CO

co LU

L2- I LL_ LU—LU— LU OICM

LU

1 . lu—o CM

CO

LU

co O

U_ I lu— lu — lu

co

LU

I

<n i

IICM LU

LU

oLO

CNI

CM

LU

CM CO LU LU

OICM

5 ”

* O O

0—0—LU_ LU= CM

CM LU

LU

co O

Li- I LL_ LU— LU— C ) CM

LU

II

CO

LL. Qu

co LU

LI- I U_

LU —LU— LU OICM LU

I

co

co CD LU cm

II I 31 LU—CD— LU — LU* LU

CM LU

co O

LL_ | LL_ O-LU-LU

CO

LU—LU— LU

28

FIGURE

4
Acronym DILUENTS Mol.Weight

EBPADMA

Bis-MPTMS

TEGDMA

HMDMA

° c

CHj=C—C-O C

CH,

CH2 — C-C -OCHrCH-CHr Si - O

CH3 ch.

CH,

C

l CH,

O

II oII c h/=c

c Hj-c Hro]h c- c =ch2 CH, CH,

o o

CHf= C “ C - O -{ CH 2}t 0-C“C=CHJ CH, CH,

540

387

286

254

Figure 5 DILUENT MONOMERS
Figure 6

SHRINKAGE vs. CONVERSION

30
TABLE 1

COMPOSITION AND PROPERTIES OF POLYFLUORORESIN BASED COMPOSITES

Resin

Composition (wt %)

Polym. Mode,

Setting Time

(Min)

P/L Ratio

(Type of

Filler

)

PFUMA (67.4)

HMDMA (31.7)

VLA 3

CQ (0.2) (Fused Quartz)

4-EDMAB (0.7) •

PFUMA (69.1 ) BIS-MPTMS (30-0)

VLA 3

CQ (0.2)

4-EDMA3 (0.7)

(Fused Quartz)

Commercial Composites VLA

2 4- Hour

Strength

DTS

Water

Sorption

(mg/ cm

2

)

Percent

Volume

Contraction

After 24 hours

47 0.21 2.8

45 0.20 2.3

25-55 0.30-0.80 2.8-4.

VLA = visible light activation

31
TABLE 2 MONOMERS USED IN THIS STUDY

ACRONYM

BIS-MPTMS

BIS-GMA

BIS-IPMA

UDMA

EBPADMA

TEGDMA

CHEMICAL STRUCTURE

MOLECULAR

WEIGHT SOURCE

O CH,

It I CHI =C-C-OCHJ —CH -CH,— Si -

I CH, CH,

387 PETRARCH SYSTEMS, INC BRISTOL, PA

FREEMAN CHEMICAL

PORT WASHINGTON, WI

o

n =c—cI CH,

OCH-CH,—

I CH,

480 ESPE

GMBH, W. GERMANY

o

li CH, = C-C-O-CH,

O

n -CH,OC-NH—

CH,

DETREY AG

ZURICH, SWITZERLAND

CH,

O

^C-C-O—(CH,CH,o)r(Q)--

CH,

N '

CH,

I C

I CH,

CH, = C-C -0-{CH, CH,0^-(!-C = CH,

CH, CH,

540 ESSCHEM

ESS1NGT0N, PA

286

32
PHYSICAL

PROPERTIES

OF

COMPOSITES

MADE

WITH

SILOXANE-CONTAINING

RESINS eoP PS Ps ps> PS PS Ps PS PS Ps

p Ps

4-1 sO cn *0- sO vO SO

p sO CM sO P m

a S>

O

O o O o © o © o o O

O P CSI 0) • • • • • • • • • • • • o s a o O o o o o o o o o © o

CO o SP sp SP >P Sp sp VP VP Sp

"O

U 00p sO cn

p cn CM o Os fH

m rv rv

<u s CO rv >a- cn

p rH

p s3- CM CM CMp

4J ></ • • • • • • • • • • • • CO O o O © o o o o o o O o

CO

<U Oj ps > 2 > p's ps PS rs Ps PS Ps PS Ps Ps PS P 0) o rs m rv CM p oo o p rv in rv

<8 jr o CM

m

pp P p

p CM CM

p cn

p

CO 4-1

wp sp sp VP sp sp VP Sp Sp sp

(U 00 TJ P c p CM cn *3- CM o cn

m o O oo sO 00

a a) CO P sr cn MT CM Os cn «a- o CM P P a p O 4-1 o CO

sp CM CM CM CM CM

p CM CM CM CM CM CM

<U PP

09 CO C ftj Ps

a> 2 > Ps /s /s Ps Ps Ps PS Ps Ps P's PS H 0) P P CM cn cn CM cn cn s3- CM p CM o sp sp sp sp sp sp VP VP Sp Sp sp P 4J

(0 Ofl T3 rv OS cn

m o cn o rv

O o inO P C p -a- '3- sa- sa- s3" m sa- s3- m sa- sj4-1 0) CO

0> P e 4J

CO co o

vp

T3P3

cr P m in

tJ o • • \ P cn in vO in in sO sa- in s

*3- in

m P 4J

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Pm

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<u 2 o o o o o o cs o o o o o p t P cn in cn m cn in cn in c co 3 o w U CO w V

09

co po

p

(p <- xi O 09 Pb <* c O M a) p

O. cn 1 CO 1 CO $ Q

e- >s a) M p £ co H (si CQ co © 0d | 33
TABLE

co

Cl] EhM

co2E8

CO<

CQV

coM

COEO

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taMg

co

04s

04o co 4—

•H CO o in CO o rH O o

Q< >

WCM 0 • o • o • o t o o e d _

cou ' ' ' ll ' , \ TJ CO in CO

J-i Cri 4-i VO in 0 E CO • • • § 4J w o o o o

(0

01 CL ,—

<r—

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co x:

a '—

— ' '

0> 4J CM <T\

O co

l-i a c 4J i-t ro CO CM

CM (N CM CM (M

g 0 CO U

CO 0

1—

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CO CO

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4-J E E MM 0 < <

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CQ N c y <#> <#> d£> <#> 0 O O O O •4—

Y r- t*- r4J co •H M <£ < <

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y E Q C O CO n Q CL-H <#> Y | Y Y E CO O co CO co co 0 0 O M (H M M o a: i—t CD m ffi CD

34
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 product 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 hydroxyapatite, 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. Buttersworths , 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. _6l_, 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. J_6 619, 1982.

[11] Antonucci, J.M., Aldehyde methacrylates derived from

hydroxy^benzaldehydes , 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] Asraussen, E. and Munksgaard, E.C., Bonding of restorative resins to

dentin by means of methacryloyl chloride and

raethacryloyl-iR^isocyanate , Scand. J. Dent. Res. 9J_ 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.

35
[15] Bowen, R.L. and Cobb, E.N. A method of bonding to dentin and enamel,

JADA _1_07 734, 1983.

[ 1 6 ] Bowen, R.L., Cobb, E.N. and Misra, D.N., Adhesive bonding by surface

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

1984.

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

composites, J. Dent. Res. 1180, 1982.

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

restorative materials, J. Dent. Res. 63 199, Abstr 255, 1984.

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

of in vivo worn dental composite restorations, J. Dent. Res. 63 675,

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. £2 126,

1983.

[22] ibid., Hydrolytic degradation of dental composites, J. Dent. Res. 6_3 1248, 1984.

[23] McKinney, J.E., Influence of acids on wear of composite restorati ves , J. Dent. Res. 63 199 Abstr 256, 1984.

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

surface energy dental composites from a polyfluorinated prepolynmer

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-flcontaining dental composites, J. Dent. Res. ^4 178, 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. 285, Abst. 1047,

1983.

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

initiator systems based on polythiols, J. Dent. Res. 6j_ 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. 6_3, 199, Abst. 257, 1984.

[29] deRijk, W.G., Conner, M.L., Jenning3, K.A. and Wu, W. , The j_n vivo wear resistance of dental composites with enhanced polymerization: J.

Dent. Res. 63 286, Abst. 951, 1983.

36
[30] Antonucci, J.M., New monomers for use in dentistry, Biomedical and

Dental 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 polyfluorinated prepolymer multifunctional urethane methacrylate, -J. Dent. Res. 64 209, Abst. 308, 1985.

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

shrinkage of photoactivated resin based materials, J. Dent. Res. 6>4 229, Abst. 488, 1985.

[33] Antonucci, J.M., Venz, S., Dudderar, D.J., Pham, M.C., Stansbury,

J.W., Non4aqueous polycarboxyate cements based on dimer and trimer

acids, J. Dent. Res. 63 294, Abst. 394, 1984.

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

J.W., Energy-iab sorbing , hydrophobic dental cements based on dimer and

trimer acids, Second World Congress on Biomaterials, 10th Annual

Meeting of the Society of Biomaterials, Transactions, VII, 137, 1984.

[35] Dudderar, D.J., Esthetic, non-tori ttle dental cements based on dimer

acid, J. Dent. Res. _64 163 , Abst. H6, 1985.

[ 36 ] 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.

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

composite resins. II. Heat treatments and etching characteristics,

ibid 748, 1976.

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

1983.

37
Manuscripts accepted for Publication

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

Encyclopedia of Polymer Science and Engineering, Vol. V,

WileyMInterscience, NY, NY (1985) (in press).

2. Resin Based Dental Composites An Overview, Proceedings of the 2nd

International Conference on Polymers in Medicine, Biomedical and

Pharmaceutical Applications, Capri, Italy, (in press) (1985)

Manuscripts under review (WERB)

1. Dental Resin and Initiator Systems Based on Polythiol3, J.M.

Antonucci, J.W. Stansbury, D.J. Dudderar and S. Venz.

2. Effect of a Polythiol on the Degree of Polymerization of Resins,

S.Venz and J.M. Antonucci.

3. Non^aqueous Polycarboxylate Cements Based on Dimer and Trimer acids,

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

4. Microleakage and Water Sorption of Hydrophilic and Hydrophobic Dental

Composites, S. Venz, N.W. Rupp and J.W. Antonucci.

5. Synthesis of a Polyfluorinated Prepolymer Multifunctional Urethane

Methacrylate, J.M. Antonucci, J.W. Stansbury and S. Venz.

6. Esthetic, Non^brittle Dental Cements Based on Dimer Acid, D.J.

Dudderar and J.M. Antonucci.

7. Evaluation of Sioxane^containing Dental Composites, J.S. Kuo, J.M.

Antonucci and W. Wu.

Invited talks

1. Fluoropolymer Applications in Dental Materials, Fluoropolymer

Workshop, Naval Research Laboratory, Washington, D.C., Feb., 1984.

2. Resin Based Dental Composites. An Overview, 2nd International

Conference on Polymers in Medicine, Biomedical and Pharmaceutical

Applications, June, 1985, Capri, Italy.

3. Low Surface Energy Dental Composites From Polyfluorinated Prepolymer

Multifunctional Methacrylates, 2nd International Conference on Polymers in Medicine, Biomedical and Pharmaceutical Applications,

June, 1985, Capri, Italy.

4. Properties of Hydrophobic, Energy-»Absorbing Cements, Dental Materials

Conference, St. Andrews, Scotland, Sept. 1985.

1 38
IADR/AADR/1 985

1 . Synthesis of a polyfluorinated prepolymer multifunctional urethane

methacrylate, J.M. Antonucci, J.W. Stansbury and S. Venz.

2. Evaluation of siloxane^containing dental composites, J.S. Kuo, J.M.

Antonucci and W. Wu.

3. Degree of cure and polymerization shrinkage of photcaotivated resin

based materials, S. Venz and J.M. Antonucci.

4. Wear and microhardness of ionomer cements, J.E. McKinney, J.M.

Antonucci and N.W. Rupp.

5. Detection of lead in human teeth by exposure to aqueous sulfide

solutions, A. Sugawara, J.M. Antonucci and G.C. Paffenbarger

6. Esthetic, non^brittle dental cements based on dimer acid, D.J.

Dudderar (Hatton award competition 4 J.M. Antonucci, Proctor)

39
II. WEAR RESISTANCE AND DURABILITY ASSESSMENT OF DENTAL COMPOSITE

* RESTORATIVE MATERIALS

General Overview - This part of the annual report includes descriptions

and results of experimental procedures used by us (the NBS Dental and

Medical Materials Group) to evaluate the performance of dental composite

restorative materials. The methods employ both iri vivo and iri vitro wear

testing, microhardness, viscoelastic measurements, and microdefect

analyses. The objectives are to use appropriate techniques to define and

delineate fundamental wear mechanisms applicable to the in vitro 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 Assessment of Composite Restoratives

Phase I. Experimental composites with flexible chain polymers

Phase II. Ionomer cements - conventional

Phase III. Ionomer cements - metal filled

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

Phase I. Torsional rheometer measurements

A. Wear and Durability Assessment of Composite Restoratives

Background

From microdefect analyses [1] on In vivo worn restoration biopsies,

environmental-generated damage was observed [2] on both occlusal and

nonstress-bearing surfaces of composite restorations. Accordingly,

the intraoral chemistry is believed to play a large role on the in

vivo degradation of these materials. For this reason a relevant

wear test should include the influence of a simulated intraoral

environment. Accordingly, the wear test specimens are preconditioned

in appropriate liquids prior to wear testing. Since dental composites

comprise two major components, polymer matrix and Inorganic

reinforcing filler, relevant preconditioning media were chosen which

have damage potential to these components.

Previous work at NBS has shown that the _in vitro wear resistance and

microhardness of dental composite specimens preconditioned in organic

food-simulating liquids [3] are commensurate with the extent of

solvent-induced damage. [4,5] As the solubility parameter of the

solvents was varied by selecting appropriate food-simulating liquids,

the wear resistance and hardness minimized at a solubility parameter

value corresponding to that of the matrix polymer. Accordingly, the

results suggest the selection of matrix polymers having solubility

parameter values out of the range of those of liquids encountered

intraorally

40
During this reporting period a manuscript describing this work was prepared and approved for publication by the Journal of Dental

Research.

Increasing the degree of cure of the matrix polymer by elevating the cure temperature improved the wear resistance of the composite

specimens. [ 6 , 7 * 8 ] A higher degree of cure produced a more rigid

and closely packed polymer matrix, which, in turn, inhibited the

diffusion of liquid penetrants capable of producing surface damage.

Since elevating the cure temperature by a sufficient amount in situ

is considered to be impractical, an alternative was to develop a flexible-chain polymer which will reach a sufficiently high degree of

cure at the in situ temperature, 37 °C.

Our work on the influence of intraoral acids, and even water, on the

degradation of certain commercial composites has revealed decreases

in microhardness and wear resistance. [9] More severe consequences

were observed on composites employing modified glass fillers to

obtain radiopacity than on those employing pure silica fillers. The

failure mode results from stress corrosion of the filler causing a breakdown at the interface. For this reason we have turned our attention to ionomer cements which have tight ionic bonds between

polymeric matrix and glass filler resulting in a more continuous

interface.

The cure process of the ionomer cements does not seem to be as viscosity limited as with the resin-based composites. Accordingly,

higher degrees of cure can be reached at the in situ temperature with

ionomer cements.

Objective

The objective of this task is to identify the _in vivo wear and

degradation mechanisms of dental composite restorat ions. The

results, when correlated with in vivo tests, facilitate the

development of new dental composite materials.

PROGRESS REPORT

Phase I

Experimental composites with flexible-chain polymers. —Microhardness measurements have been made on several

composites employing flexible-chain polymers and these polymers

in neat form. A large portion of this work was done by a research associate from Dentsply International. As with the more conventional composites, preconditioning was done in

appropriate organic liquids. With new composites and their

polymers, of which most were si loxane-containing or fluorinated

copolymers, the microhardness of the preconditioned specimens

minimized at lower solubility-parameter values than that for the

more conventional composites and their polymers, e.g., BIS-GMA.

41
Wear measurements were initiated on an experimental composite

containing a 70/30 PFUMA/BIS-MPTMS^ matrix polymer. The

specimens were preconditioned in 100$ ethanol and in pure water.

Previous microhardness measurements over a solubility-parameter

scan revealed a minimum corresponding to the solubility

parameter of pure ethanol. The degree of softening determined

from the Knoop Hardness Numbers of the 100$

ethanol-preconditioned specimens was larger than that of any

dental composite we have tested. There was no effect, however,

on the water-preconditioned specimen.

On the other hand, the initial wear was very small and about the same for both kinds of preconditioning. Although the

steady-state wear was large, it was about the same for both

cases. Even though the composite was subject to extreme

softening in ethanol, the wear was stable. This paradox,

apparently, results from the high degree of crosslinking in this

polymer and its more rubberlike character which allows

softening, but limits decomposition or breakdown during wear.

Phase II

Ionomer cements - conventional. — Wear and microhardness

measurements [ 10 ] were made by NBS on preconditioned commercial

specimens of essentially the same content. The preconditioning

media were air, water, and 0.02 N lactic acid. As usual, the

preconditioning period was one week. With the air-preconditioned

specimens, the hardness increased by nearly a factor of three,

and wear studies were essentially impossible due to the

catastrophic failure resulting from brittle fracture of the

dehydrated specimens. With the lactic-acid preconditioning, the

hardness fell markedly with a corresponding decrease in wear resistance. Since lactic acid is generated from plaque

formation, ' it is intraorally omnipresent in many people. This

kind of chemical instability is a serious limitation to the

application of ionomer cements as presently formulated.

Phase III

Ionomer cements - metal filled. — Wear and raicrohardness

measurements were extended to include a commercial

silver-modified ionomer cement. As with the more conventional

ionomer cements, the hardness declined the most during the

lactic acid preconditioning; however, the differences between

the results from different precondit ioning media were less.

With both the water and lactic acid treated specimens the wear resistance increased considerably over that of the more conventional ionomer cements. The silver appears to provide a lubricating effect. On the other hand, the susceptibility to

brittle fracture during wear does not appear to be improved by

1 For more details on the formulations and synthesis of this polymeric

system, see Part I, Section E.

42
the addition of combined silver. SEM microdefect analysis

revealed some damage to the si'lver-f illed ionoraer cements

preconditioned in 0.02 N lactic acid. The extent of damage was

not as much as that observed for the more conventional ones.

B. Gla33-Transition Temperature (T^) of Matrix Polymers

Background

As stated in the last section, dental composite restorations may be

made more durable by increasing the degree of cure of the matrix

polymer. In addition, we have determined that both the in vitro wear

resistance and micro-hardness are increased by increasing the degree

of cure through elevation of the cure temperature, T

c

. [6,7,8] Since

this method of increasing the degree of cure is considered to be

impractical for in situ placed restorations, an alternative must be

considered.

The problem with free-radical cured systems, of which BIS-GMA is an example, is depicted in Figure 1 where the glass transition

temperature, Ta , or the degree of cure, x, is plotted against cure

time at the isotherm, 1 . As the cure proceeds, T_ or x will

increase until Tg approximates T^ at which the cure

3 essentially

terminates prematurely. [11] The limited degree of cure results from

an increase in molecular ' viscosity , which prevents reactive groups

from becoming proximate. Since these groups cannot react with each

other to form crosslinks, the degree of cure is essentially limited

at a terminal value, and the pendant vinyl groups can have a plasticizing effect on the matrix and serve as potential sites for

oxidative attack.

From Figure 1 , it is evident that the degree of cure may be increased

by either increasing T

Q or decreasing Tgo,, the value of T

g corresponding to a completely cured system for which x = 1 , to make

the difference Tg* - T

c smaller. Since in clinical applications

increasing T

c is impractical, the alternative of the polymer is to

decrease Tg,,,. This procedure is more difficult in that it involves

nontrivial changes in chemical structure for which more detailed

narratives are given in Part I, Section E. These involve

silaxane-containing copolymers and fluorinated copolymers to produce

flexible chains. In addition the solubility parameters of these

polymers are expected to have lower values than those of the typical

dental polymer. This, in turn, is expected to reduce the interaction

with the organic liquids present in foods.

Objective

The objective of this task is to determine the glass-transition

temperature of selected dental polymers as a function of cure

temperature

43
Glass

Transition

Temperature,

PROGESS REPORT

Phase I

Torsional rheometer measurements. — T measurements [12] have

been made on pure BIS-GMA and 70/30 BIS-GMA/TEGDMA polymers in

collaboration with a guest worker from The Taiwan National

University using a Weisenberg Rheogoniometer . This viscoelastic

technique employs forced vibration in torsion at constant

frequency (in this case 1.9 Hz). From a temperature scan, T

g

is

determined from the temperature at which the energy dissipated

is a maximum. For example, at a cure temperature of T

Q

= 183 °C,

the measured'Tg is about 178 °C for both polymers. This value of

T

e is much less than T20B because a complete cure is still not

For our 90 °C for

obtained even at this elevated temperature.

application, we desire

which Ta00 -To = 53

37 °C.

a polymer with Tg(X) at about

„ j

.

q

- jj °C with Tc here, the in situ cure temperature,

A value of T„.p-o, too high produces an undercure, A value

too low produces a rubber-like material, which is not useful for

restorative application. Thus the determination of T

g

is useful, or perhaps even essential, to optimize these materials with

respect to long term in vivo durability.

FIGURE 1

This determination also gives the shear moduli above and below

T_, which are useful for development of these materials.

&

0

i—

D

o

0

0

CD

0Q

0

Schematic variation of the glass transition temperature

;g or degree of cure x with cure time. When T

g -I

c

, where -j

the cure temperature, the curing process terminates.

*c

44
References

[1] Wu, W. and Cobb, E. A silver staining technique for investigating

wear of restorative dental composites, J. Bioraed. Mat. Res.

15:343-348, 1981. * . . .

[2] Wu, W. , Toth, E.E., Moffa, J.F. and Ellison, J.A. Subsurface damage

of in vivo worn dental composite restorations, J. Dent. Res.

63:675-680, 1984.

[3] FDA Guidelines for chemistry and technology requirements of indirect

additive petitious. Mar. 1976.

[4] Wu, W. and McKinney, J.E. Influence of chemicals on wear of dental

composites, J. Dent. Res. 61:1180-1183, 1983.

[5] McKinney, J.E. and Wu, W. Influence of chemical softening on wear of

three types of dental composites, IADR Prog, and Abstr. 61:271,

Abstr. No. 831, 1982.

[6] McKinney, J.E. and Wu, W. Effect of degree of cure on hardness and

wear of three commercial dental composites, AADR Abstr. 62:285,

Abstr. 1047, 1983.

[7] Wu, W. Degree of cure and wear resistance of dental composites, IADR

Abstr. 62:671, Abstr. No. 192, 1983.

[8] de Rijk, W.G., Conner, M.L., Jennings, K.A., and Wu, W. The in vivo

wear resistance of dental composites with enhanced polymerization,

ibid , Abstr. No. 951.

[9] McKinney, J.E. Influence of acids on wear of composite restoratives,

IADR Abstr. 63:199, Abstr. No. 256, 1984.

[10] McKinney, J.E., Antonucci, J.M. and Rupp, N.W. Wear microhardness of

ionomer cements, IADR. 64: 371 , Abstr . 1767, '1985.

[11] Gillham, J.K. Formation and properties of network polymeric

materials, Polyra. Eng. and Sci. 19:676-682, 1979.

[12] Wu, W. and Yu, C.C. Glass transition temperature of dental composite

resins, IADR Abstr.' 64:229, Abstr. No. 487, 1985.

45
Publications

Environmental Damage and Wear of Dental Composite Restoratives, J.E.

McKinney, Proc. Inti. Symp. Resin Based Posterior Materials, Mullet Bay,

St. Maarten, Neth. Ant., ed. D.C. Smith and G. VanHerle, Jan. 1985.

Manuscripts Accepted for Publication

Chemical Softening and Wear of Dental Composites, J.E. McKinney and W. Wu,

J. Dent. Res. (in press)

Manuscripts Under Review

An In Vitro Comparison of the Wear Rates of Acrylic, IPN, and Microfilled

Denture Tooth Materials, D.J. Whitman, J.E. McKinney, R.W. Hinman, R.A.

Hesby, and G.B. Pelleu, ' Jr., Submitted' to J. Prosth. Dent. for

publication.

Invited Talks

Environmental Damage and Wear of Dental Composite Restorations, J.E.

McKinney, Proc. Inti. Symp. on Posterior Composites, Mullet Bay, St.

Maarten, Netherlands Antilles, eds. D.C. Smith and G. VanHerle, Jan. 1985.

(Corresponding publication entered separately).

Contributed Talks

Wear and Microhardness of Ionomer Cements, J.E. McKinney, J.M. Antonucci,

and N.W. Rupp, IADR Abstracts 64, No. 1767 (1985)

Glass Transition Temperature of Dental Composite Resins, W. Wu and C.C.

Yu. IADR Abstracts 64, No. 487 (1985)

46
III. DENTAL ALLOYS AND CERAMICS (AND METROLOGY)

General 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 crowns comprise a significant fraction of those protheses fabricated. Because the newly

introduced alloys can vary considerably in ' their fabrication

characteristics and clinical performance, more reliable methods than now

exist are desired 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 the

porcelain-alloy thermal-stress compatibility, the porcelain-to-metal

system strength, alloy castability 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 aid 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 stress has its origin in the differences in

thermal expansion which exist between porcelain and alloy throughout

the firing temperature range. Other properties which also affect the

build up or retention of stress include the thermo-plastic properties

(primarily of the porcelain), thermal conductivity, and

temperature-dependent elastic moduli. Geometric variations in

restorations are also contributing factors. Thi3 study was undertaken

to define the thermo-mechanical stress compatibility in terms of

those parameters.

Accomplishments

The objective of this part of the investigation was to explore the

potential of using the gap of a procelain veneered split metal ring as

a means for determining the thermal-stress compatibility between the

porcelain veneer and the metal substrate. The change in gap upon

cooling from the veneering temperature is the effect measured and

desired. For this purpose several finite-element models (FEM’s) had

been developed, each to assess in a preliminary manner the material

properties required and the graphic grid and computer program

necessary to provide good insight into the compatibility problem.

Earlier work reported on [1,2] indicated that the porcelain ring

composite would be highly indicative of viscous relaxation behavior of

47
the porcelain (two porcelains with nearly the same values of a, the

coefficient of thermal expansion, had shown greatly different gap

changes). It was considered necessary to obtain the temperature

dependence of the elastic modulus of several porcelain and alloys in

order to refine calculations of gap changes. (These changes are then

to be correlated with experimentally-determined values. Ultimately,

it is expected that tables of properties and stress, etc., or simplified regression equations or other techniques can be developed

which will describe thermal stress compatibility, with the split ring

serving as the experimental check on the methods employed. It should

be noted that the resultant description of compatibility should be

generally applicable for any veneering process using thermal

techniques provided the critical material properties are adequately

described. . .one intent was to confirm what the critical properties

are)

Phase I

During the previous period, progress had been made in

determining the temperature-dependent elastic moduli for three

alloys and two porcelains. One manuscript (see publications

#1)* has been published ' in this period and another (see

manuscripts in review**) has been submitted for publication.

Also determined were the surface temperature differences between

porcelain and metal during cooling of a split ring having

thicknesses , of 0.8 mm of porcelain and 0.5 mm of metal. The

maximum temperature difference was 35 °C, reached shortly after

cooling from 980 °C.

Phase II

These data, along with previously obtained results on temperature-dependent viscosities of the porcelains [3] and

their thermal expansions [1] will be used, in a refined finite

element program (under construction) on analysis of gap change,

(and resultant stresses) as functions of these parameters and

cooling conditions.

Phase III

Finalize material input parameters for split ring computer

program and fine tuning for match with experimental results.

Planned for FY 86.

Phase IV

Devise 3imple analytical representation of split ring

stress-strain calculations, if possible.

Phase V

Examine results of FEM vs 2-dimensional theory developed by

Scherer. FY 87. [4]

48
B. Porcelain-Alloy Compatibility (Bonded System Strength)

PROGRESS REPORT

Overview

Numerous tests have been proposed by others [5, 6, 7, for example]

for the purpose of evaluating the porcelain-metal bond strength

(PMBS). Some are qualitative in essence, others attempt to test in

shear even though brittle materials fail in tension (porcelain and

the nonmetallic interface are brittle). Often, the test designs

involve curved or sharp boundaries between the porcelain and the

metal, further complicating any analysis (qualitative or quantitative) because of the crack initiation aspects of such stress

raisers.

In an attemp’t to overcome the forementioned difficulties, a bending

beam composite (BBC) specimen was designed for evaluation. The

specimen is prepared to provide all smooth surfaces at

porcelain-metal junctions when subjected to the proper bending moment

and creates tension at the bond and within the porcelain. Alignment

of the specimen is not critical (misalignment by a few degrees about

an axis perpendicular to the horizontal plane of the specimen results

in only a few tenths of a percent effect on the calculated stress).

Three-dimensional finite element and two dimensional finite-element

stress analyses showed good agreement with beam theory analysis.

Accomplishments

Phase I

Test fractures for the BBC were not isolated to only the

interface, but were distributed through the porcelain (lying in,

near, or 1-2 mm away from the interface. It is apparent that

what is really being evaluated is porcelain fused-to-metal

system strength; this is also what is clinically important. It

also became understood that every other dental

porcelain-to-metal bond test in the literature is in reality

testing porcelain-metal system strength. With this in mind all

fracture data were grouped in cumulative failure plots for each

system tested and graphically-distinct differences could be

discerned where the simple application of normal distribution

statistical analyses revealed none. Because we are dealing with

brittle fracture in ceramic materials (by observation ... also

,

the metal is not expected to fail as the lowest metal-yield

strength is -3X the tensile strength of the porcelains) Weibull

statistics curve fitting (cumulative failure) is deemed the

appropriate approach.

One paper on the feature of specimen design, and stress analyses

has been prepared. (See manuscripts in review, # 2) It will be

submitted for publication with another manuscript which is

currently in preparation and deals with the Weibull analysis. It

is considered important to publish these two papers together as each lends substance to the other. For this reason the first

manuscript has not yet been published.

49
The Weibull method has been chosen to provide more convenient

and significant differentiation between porcelain-metal bonded

systems. It is proposed to explore two- and three-parameter

Weibull' plots for fitting of fracture data. Generally,

according to Weibull for a large sample of data, the probability

of failure at a given stress level P(a) may be represented by:

where a is the level of stress

aQ is a characteristic stress

is a threshold stress (Oi >0) m is a shape or distribution parameter.

As an example, let = 0. Then two porcelains with the same

a Q , but with different values of m would plot as shown in figure

1 .

Figure 1

The average, or mean values of these two porcelains would be

nearly the same, (this is slightly oversimplified, but this

approximation is used to demonstrate the usefulness of the

Weibull approach). Hence, these systems would be virtually

indistinguishable by simple normal distribution statistical

analysis, yet it is clear that system #1 (Figure 1) is more prone to failure at lower stresses. This is expected to be of

clinical significance. For example, system 1 could be expected

to have many more early clinical failures due to the to failures

at low stress levels. The application of Weibull analysis coul 1 lead to greater understanding and definition of critical

50
parameters for improving dental porcelain-metal systems.

Further, the analysis and four-point bend test is not restricted

to porcelain-metal systems, it should find applicability for

other dental bonded systems, such as enamel-to-resin

dentin-to-resin , composite-to-metal and so forth.

Phase II

Determine three dimensional and two dimensional FEM of BBC.

This phase was completed in FY 83.

Phase III

Determine theoretical curve fitting methods: exploration of

3-Parameter Weibul analysis. Under investigation. . .will pursue

in FY 86.

Phase IV

Photo elastic study of BBC... to be explored in FY 86 and 87, if

deemed necessary.

Phase V

Explore effects of alloy reuse, specimen reuse, annealing of

porcelain, immersion in water (or saline solution) on system

strength. To be initiated in FY 86.

C. Castability (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. Asgar [8] described a method using a spiral pattern. The length of spiral that was cast was used to

provide a quantitative measure of the ability to cast an alloy.

Obtaining consistent, nearly identical patterns with a constant pitch

for all spirals and constant diameter could be a difficulty

encountered with the use of such a method and would complicate the

length-measurement process. Sorensen and Ingersoll [9] used a stainless-steel mold to produce patterns in the shape of a six-spoked

wheel with thin web sections between the spokes to indicate fluidity

of gold casting alloys.. Obtaining a quantitative measure of

cast-ability of an alloy is virtually impossible with that pattern,

although good qualitative information can be derived. Vincent et al.

[10] describe a method for measuring castability by using a pattern

51
with a range of rod diameters. Quantitative and qualitative

information is available from this technique, and it does allow for

separation of some aspects of castability. This technique also

requires a precise measurement of length to -0.1 mm. Preston and

Berger [ 11 ] employed a spring-shaped pattern similar to Asgar's while

Nielsen and Shalita [ 12 ] and Barreto et al. [ 13 ] have used various

configurations of a wedge; these also require precise and microscopic

measurements. Smith et al. [ 14 ] studied both castability and fit

together using a simulated molar crown scribed with lines for

measurements with a traveling microscope. Nielson et al. [ 15 ] have

developed a razor monitor which is capable of relating effects of

variables such as alloy temperature and mold temperature in terms of

reproduction of fine detail.

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 employing 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.

Accomplishments

Phase I

Statistical and functional representation of castability. One

manuscript has been published (Publication #2) entitled "A

Technique for Characterizing the Casting Behavior of Dental

Alloys". Another manuscript, "Castability of Dental Alloys,

Mold and Alloy Temperature Effects", has been prepared and is

under internal review.

Phase II

Analysis of Effects of Composition on Castability. The first

determinations of this have been made, using data available from

the six alloys mentioned in Phase I. The following equation was

found:

52
c = K + K [Si] + K [B] + K [Cb x Sn] + K [A1 x 3e] + v o 1 2 3 4 t

[Mo x Mn]

Where : K* = function of mold and alloy temperature

[J = concentration of elements

This expression needs further refinement as it is not certain

that the terms involving products of elemental compositions are sufficiently independent in each element, that is, some particular compositions appear to be too strongly correlated.

Also, to be strictly correct, only one investment should be used

for obtaining the castability data whereas 3 were used for the

earlier parts of this program. However, at this point, the

technique has been demonstrated to be a viable method for

analyis. A manuscript (publication #5) on this was prepared for

presentation as an invited paper at an International Precious

Metals Institute Meeting in Israel, April 1985.

For the six alloys in question, preliminary results have shown

the temperature-dependent effects on for B and Si ( Figures

2 and 3). Determinations of K^’s will be useful for computer

aided design of dental alloys.

ELEMENT: Boron

Catting Temp. (Tc), (Degrees Celsius)

Figure 2: Effect of alloy casting temperature on constant, K-,

,

(equation 3a, text) for boron. The alloy is a Ni-Cr

based alloy.

53
V V

Casting Temp. (Tc), (Degrees Celsius)

Figure 3

’ Effect of alloy casting temperature on constant, , (equation 3A, text) for silicon. The alloy is a Ni-Cr based alloy.

Phase III

In order to investigate the effects of investments on C yt , one alloy (from one batch) was cast into several investment batches

of the same brand of investment. The results showed that for

two different batches of investment, 1 and 2, this previously

found equation for the transformed castability value, C

y t

, is:

C

v, tl a1 + b

1 TA

1/2 2

T

M

C v , t2

1/2 2 a + T T

2 bl A M

where TA

is the alloy superheat temperature, given by T

A

- T^ - T

s , and Tq = the casting temperature, T3

=* the alloy solidus

temperature. TM

= the mold temperature.

In these equations "b" remained unaffected, with the effect of

batch showing on the term', a', . Hence the temperature dependence

of Cyt is unaffected by batch variation; (note; however, Cyt. is

changed through changes in the constant, a). This result may

prove useful in correcting laboratory procedures, if necessary,

when batches are changed and indicates the desirability of

maintaining as large a supply of one batch of investment as possible in order to avoid encountering casting problems from

changing batches. It is conceivable that C yt might also be used

to characterize Investments with a standard alloy. A manuscript

on preliminary results has been published, [see publication S 5]

54
D. Castability (Accuracy of Fit of Dental Castings)

PROGRESS REPORT

Overview

Because base metal alloys had come into widespread use Eden et al.

[16] investigated the reasons for their often producing tight fitting

castings. They demonstrated that satisfactory oversized single unit

castings could be achieved routinely with a modified investing

technique. Although this technique worked with single units

centrally ' located in the investing ring, the question arose as to how

well it might work with multiple unit castings. An extension of this

study by Hinman and co-workers revealed the conditions under which

multiple unit castings produced the best fit. It was found that

pattern distortion apparently was greater " than mold expansion

distortion and that a bench set technique with an all wax pattern

system (pattern, prues, runner bars) produced the most consistently

accurate dental castings.

In view of these results and early results of Marsaw [17] it appeared

that the internal setting expansion of dental investments was lower

than and quite different from that obtained from external

measurements and run by manufacturers according to ADA measurement

techniques. A similar finding of lower internal expansion had been

obtained many years ago by Asgar [18] on gypsum investments.

The ballon techniques of Asgar et al. and Marsaw et al. are difficult,

to set up and monitor and the casting techniques are not sufficiently

controllable to separate the effects of many variables on setting

expansion. Hence, some preliminary studies using strain gauges were

considered for investigating internal setting expansion. It was reasoned that a strain gauge might act very much like a pattern and

not begin to change shape until the investment was sufficiently set

to deform it. Therefore, it seemed to provide a reasonable approach

toward isolating setting expansion from other unknown efforts such as pattern distortion. The strain gauges are small and planar and

measure expansion in only one direction.

Accomplishments

One paper on the fit of multiple unit fixed partial dentures was published in this reporting period (publication #4).

Phase I

Preliminary experiments on the use of strain gauges were conducted and the findings published (see publications, ?/6).

These results confirmed the earlier results of Marsaw and of

Asgar and their co-workers in that the internal setting

expansion was indicated to be much smaller (-0.101) than

manufacturers indicate from their external measurements (-11)

55
Phase II

This work will be continued with the following objectives: (a)

improve stability and reproducibility of individual strain gauge

measurements and (b) examine multidirectional and specific

spatial effects.

E. Solderablllty

PROGRESS REPORT

Overview

The original objective of this work was to examine whether bend or pure-tensile testing was the most effective method for evaluating the

strength of soldered joints. Following the work reported on for FY

84 it may be stated now that it is not planned to continue this work

beyond that previously reported on as the investigators do not

believe that any particular difficulties exist with either bend or tensile testing of soldered joints; hence', there is not considered a need here for development.

F. Metrology and Analysis: Measurements for Characterization of Dental

Materials or Function

PROGRESS REPORT

Overview

Although many other properties must be considered in choosing

materials for restorations and prostheses two of the primary

properties or characteristics to be considered are mechanical

strength and durability.

As a necessary adjunct to NBS dental research projects, this group

has long maintained various kinds of general purpose test and

analysis equipment such as tensile machine and hardness indentors.

These are used by researchers to conduct standard tests for strength

as well as non-standardized tests of such properties as adhesive

strength or the retention strength of prostheses for example. In

addition, this group has developed and now maintains several less

common devices in support of various projects. These include a mercury filled dilatometer for measuring the volume changes which

occur during the setting of restorative materials, apparatus for

measuring thermal expansion from room temperature to 1 500 °C and

apparatus for measuring tensile and shear moduli from room temperature to 500 °C.

Besides these devices, we are developing various test methods. These

include a four point bending test for character izat ion of the strength

of bonded dental systems such as porcelain-fused-to-metal ind

composite to metal, for example, a split ring test character iz ing

thermo-mechanical capability in veneered systems (such is

porcelain -fused to metal, ceramic to ceramic, etc.) and a castabllity

index test to quantify the ability of an alloy to produce complete

castings under various sets of conditions.

56
Objective

The objective of this project was to develop various test instruments

and methods to the point that they can be used by researchers for

routine measurement. A device for measuring the volume changes which

occur on the setting of restorative materials was needed for research

in other parts (I and II) of our program. Another section of this

effort has involved an investigation of the suitability of using the

standard diametral test [ 19 ] for evaluating the tensile strength of

modern dental composites. '

Accomplishments

Phase I

Development of a Recording Dilatometer for Measuring

Polymerization Shrinkage

A device described in the literature for measuring

polymerization shrinkage was constructed. However, this device

was thermally and mechanically unstable, ' i.e. , it required much

longer periods (several hours) for the system to stabilize

during an experimental run than the time for the polymerization

to be completed and the magnitude of the drift was of the same order or greater than that of the expected change in output due

to the polymerization.

The problem was solved by replacing the poly (methyl

methacrylate) device with a more rigid, less massive one constructed of pyrex glass and by substantially reducing the

volume of mercury. Ancillary equipment which had been developed

functioned satisfactorily with the new dilatometer. This

included a thermostatic air chamber which is stable to +_ 0.01 °C

linear variable differential transformer device for measuring

the volume changes as well as a simple pynknometer for measuring

the sample volume. The device has been shown to be sensitive to

volume changes of +_ 10

-

^ CM^ and to be stable to within those

limits for periods of several hours. The device is now in

routine use and several requests for information have been

received.

A poster presentation and manuscript describing the dilatometer

device were presented at the IADR meeting in March 1985, and a manuscript has been submitted for publication to the Journal of

Dental Materials.

This project of development of a dilatometer for measuring

polymerization shrinkage is completed. One manuscript on the

design of the dilatometer has been submitted for publication

(see manuscript in review, #5).

Phase II

Evaluation of the Suitability of Applying the Diametrical Tensile

Test for Determining the Tensile Strength of Dental Composites.

57
During the 1984 meeting of the International Association for

Dental Research the question arose among two scientists from the

NBS and University of Michigan (UM) dental groups whether the

diametrical tensile test Cl 9] remained a valid test method for

evaluating the tensile strength of modern dental composites.

These composites often contain lower amounts of filler, have

different curing systems and modified resin matrices from those

in existence at the time of development of Spec. #27. [ 19 ]

In a cooperative effort between NBS and UM to test the validity

of using the DTT for newer dental composites, four composites

were chosen for testing, each having one or more essential

difference from all others. It was reasoned that for either a deformable or viscoelastic material, the calculated failure

stresses should be strain rate dependent. Hence, forty DTT

specimens were prepared at NBS' for each composite evaluated

(Table #1 ) and divided into four equal groups for testing at

different crosshead speeds (CS) (or strain rates) of 5, 0.5,

0.05, and 0.005 cm/min. Twenty specimens were similarly

evaluated at UM.

Test results are given in Table 2. The results for each

material were fit to a regression curve of the form y

=* A+BX,

where y

= the DTS and X = the log CS. Correlation coefficients,

r, were also calculated and the ''pooled” "t” values were obtained from

The probability, a, of obtaining a t value equal to or greater

than the calculated t was obtained from a table of t values.

The results are summarized in Table 3« In the above

formulation, N = the pooled number of samples, 40 for NBS and 20

for UM.

From Table 2 we note that from the NBS evaluation significant

correlation with log CS exists at the 95 percent confidence level

(or better) for materials a, c, d, e and from the UM evaluation

for materials d and e. It should be noted that S (the estimate

of the standard deviation) is linearly related to the magnitude

of the value of Y, Fig. 1 . Hence, in order to compare effects

between materials it was necessary to transform all data to i parameter, P, which is independent of log CS. Dividing y

- A + BX

by Y accomplished this; hence, B/Y was compared for each

material. Under these conditions it can be seen in (Table 2)

that all values of B/Y are less than those for material e, in

58
accepted brittle material. It was; therefore, concluded that

each of the materials in question is functioning in a brittle

manner, as the effect of log CS on the DTS is less than its

effect on the brittle material, e.

Hence, the DTT is a viable method for determining the tensile

strength of modern dental composites. One manuscript (see

manuscript in review, #4) is in review.

TABLE 2

Parameters resulting from analysis of diametral tensile testing of composites. Regression analysis according to equation y

- A + BX and statistical

evaluation.

Material

Parameters a b c d e

NATIONAL BUREAU OF STANDARDS TESTING:

r 0.32 0.10 0.50 0.48 0.53

Y 36.9 35.6 53.3 59.6 6.7

(3.4) (4.22) (5.3) (6.2) (1.1)

B 1 .02 1 .09 2.71 2.96 0.58

B/Yx102 2.76 3.05 5.09 4.97 8.7

t 2.05 0.62 3.55 3-37 3.85

a 0.05 0.5 0.001 0.005 0.001

UNIVERSITY OF MICHIGAN TESTING:

r -0.14 ’ -0.31 0.28 0.49 0.58

Y 32.4 31 .7 49.1 51 .7 4.3

(4.0) (3.7) (4.9) (4.11) (0.71

)

B -0.51 -1 .0 1 .24 1 .99 0.43

B/Yx102 -1.6 -3.2 2.5 3.9 10.1

t 6.60 1.38 1 .24 2.38 3.02

a 0.5 0.2 <0.2 <0.05 <0.01

r - correlation coefficient

Y - mean value of all values of where Y is the breaking strength of

individual specimens tested at various crosshead speeds with standrd

deviation in parenthese.

B - regression coefficient

t - t value from standard t. tables for confidence level a, for the degrees

of freedom and standard deviation applicable

a - significance level

59
References

[1] Whitlock, R.P., Tesk, J.A., Widera, G.E.O., Holmer, A, and Parry,

E.E., Consideration of Some Factors Influencing Compatibility of

Dental Porcelains and Alloys. Part I, Thermo-Physical Properties,

Proceedings of the 4th International Precious Metals Conference,

Toronto, Canada, Pergammon Press, p. 273-282, June 1980.

[2] Tesk, J.A., Whitlock, R.P., Widera, G.E.O., Holmes, A., and Parry,

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, p. 283-291 , June 1980.

[3] Tesk, J.A., Hinman, R.W., Whitlock, R.P., Holmes, A., and Parry,

E.E., Temperture Dependence of Shear Viscosity for Several Dental

Porcelains., J. Dent. Res. 60(A), Abstract 839, p. 519, March 1981.

[4] Scherer, G.W., Viscoelastic Analysis of the Split Ring Seal, J. Am.

Cer. Soc. 66(2), p. 135-139, Feb. 1983.

[5] Shell, J.S. and Mielsen, J.P., Studyn o the Bond Between Gold Alloys

and Porcelain, J. Dent. Res. Vol. 41, 1424-1437 (1962).

[6] Anusavice, K.J., Dehoff,. P.H. and Fairhurst, C.W., Comparative

Evaluation .of Ceramic-Metal ' Bond Tests Using Finite Element Stress

Analysis, J. Dent. Res. Vol. 59, #3, 608-61 3, March 1980.

[7] Chong, M.P. and Beech, D.R., A Simple Shear Test to Evaluate the Bond

Strength of Ceramic Fused to Metal, Australian Dental Journal, Vol.

25, #6, 357-361, 1980.

[8] Asgar , K. , Metal Castings in Dentistry. In Dental Biomaterials

-Research Priorities, L.W. Wachtel, Ed. Working DC, DHEW Publication

#(NIH) 74-548, pp. 27-44, 1973.

[9] Sorensen, S.E., and Ingersol, C.E., A Method for Determining Fluidity

of Casting Gold Alloys, IADR Prog. Abst. 45: #191, 1966.

[10] Vincent, P.F., Steveven, L., and Basford, K.E., A Comparison of the

Casting Ability of Precious and Non-Precious Alloys for Porcelain

Veneering, J. Prosthet. Dent. 37: 527-536, 1977.

[11] Preston, J.D., and Berger, R., Some Laboratory Variables Affecting

Cement-Metal Alloys, Dent. Clin. N. America, 21: 717-728, 1977.

[12] Nielsen, J.P. and Nalita, S., Margin Casting Monitor, AADR Progr. and

Abstr. 56, #645, March 1977.

[13] Barrett, M.T., Goldberg, A.J., Nilkson, D.A. and Manford, G. , Effect

of Investment on Casting High-Fusing Alloys, J. Prosthet. Dent. U4:

504-507, 1980.

60
[14] Smith, C.D., Deckman, J., and Fairhurst, C.W. , An Alloy Castability

and Adaption Test, AADR Progr and Abst. 59: ' #328, March 1980.

[15] Nielson, J.P., Sumethr, N., and Cassone, P., Castbility Ranges for

Dental Alloys, J. Dent. Res. 63 » Abstract #798, March 1984.

[16] Eden, G.T., Franklin, J.M., Ohta, Y. , and Dickson, G. , Fit of

Porcelain Fused-to-metal Crown and Bridge Castings, J. Dent'. Res., 58

( 12 ).

[17] Marsaw, F.A., deRijk, W.G. , Hesby, R.A., Hinman, R.W. , Pellen, G.B.,

Internal Volumetric Setting Expansion of Casting Investments. J.

Prosthet Dent., 52: 361, 1984.

[18] Asgar, K. , Lawrence, W.N., and Peyton, F.A., Further Investigation

into the Nature of Hygroscopic Expansion of Dental Casting

Investments, J. Prosth. Dent. 8: 673. 1958.

[19] ANSI/ADA Specification #27, Direct Filling Resins, J. Amer. Dent.

Assn., Vol. 94, June 1977, pi 191.

Publications

1. Elastic Constants of two Dental Porcelain, H. R. Kase, J.A. Tesk, and

E.D. Case, J. Mats. Science, 20, 524-531, Jan., 1985.

2. A Technique for Characterizing Casting Behavior of Dental Alloys,

R. W. Hinman, J.A. Tesk, R. R. Whitlock, E.E. Parry, and J.S.

Durkowski, J. Dent. Res. 64(2') 13'4-138, Feb., 1985.

3. Physical Metallurgy of Dental Casting Alloys: sections c, Co-Cr-Mo

alloys; a, Ni-Cr alloys; e, stainless steels; f, Ti alloys in

Encyclopedia of Materials Science and Engineering, Pergamon Press,

Mar., 1985.

4. Improving the Casting Accuracy of Fixed Partial Dentures, R.W.

Hinman, J.A. Tesk, E.E. Perry and G.T. Eden, J. Prosth. Dent. 53(4),

466-471 , April 1985.

‘

5. The Mesh Monitor for Casting Characterization in Noble Metals

Fabrication and Technology Seminar, J. A. Tesk, 0. Okuno, R.W. Penn,

S. Hirano, and H.R. Kase, Proceedings International Precious Metals

Institute, Apr. 1985.

6. Internal Setting Expansion of a Dental Casting Investment Measured

with Strain Gauges, E.T. Meiser, Jr., W.G. de Rijk, J.A. Tesk, R.W.

Hinman, R.A. Hesby, and'G.B. Pelleu, J. Prost. Dent. 53(6), 870-873,

June, 1985

7. Dental Research at the National Bureau of Standards: How it changed

the practice of dental health service, G.G. Paf fenbarger , J.A. Tesk,

and W.E. Brown, J. Am. Dent. Assoc., July 1985.

61
Manuscripts in review or accepted for publication

1. Kase, H.R. and Tesk, J.A., Elastic Constants of Three Representative

Nonprecious Dental Alloys, submitted to J. Biomedicl Mate’rials

Research.

2. Tesk, J.A., Widera, G.E.O., Hinman, R.W. and de Rijk, W.G., A

Porcelain-Metal Composite Specimen for Determining System Strength.

Cleared WERB Review, to be submitted to Dent. Mats. J. with companion

paper on analysis of data.

3. Tesk, J.A., The Role of Structure and Composition on the Physical and

Biological Properties of Dental Alloys, A Review etc., to be

published in proceedings of International Workshops:

Biocompatibility, Toxicity and Hypersensitivity to Alloy Systems Used

in Dentistry, U. Michigan,

June 27, 1985. *

4. Craig, R.G., Penn, R.W. , and Tesk, J.A., Diametral Tensile Strength

and Dental Composites in Werb Review.

5. Penn, R.W. , A Dilatometer for Measuring Polymerization Shrinkage of

Dental Composites, submitted to J. Dent. Materials.

Invited talks

Characterization of the Strength of Porcelain Alloy Systems, J.A. Tesk,

Univ. of Maryland Dental School, Baltimore, MD, Mar., 1985.

The Mesh Monitor for Casting Characterization, J.A. Tesk, 0. Kuno, R.W.

Penn, S. Hirano and H.R. Kase, Noble Metals Fabrications and Technology

Seminar, Jerusalem, Israel, The International Precious Metals Institute,

Allentown, PA, April, 1985.**

The Role of Structure and Composition of the Physical and Biological

Properties of Dental Alloys, J.A. Tesk. A Review for the International

Workshop on Biocompatibility, ' Toxicity and Hypersensitivity to Alloy

Systems Used in Dentistry, The Univ. of Michigan, Ann Arbor, MI, June,

1985.

Materials for Orthopedic Implants J.A. Tesk, in Advances in

Biomedical Materials, Health Care Exp. 85, Aug., 1985

Invited and scheduled, unable to present due to poor health at that

time.

Invited, paper presented, but unable to attend due to poor health i“. that time.

62
Contributed Talks IADR/AADR Meetings

An Improved Dilatometer for Measuring Polymerization Volume Changes, R.W.

Penn, March 1985.

Diametral Tensile Strength and Dental Composites, R.G. Craig, R.W. Penn

and J.A. Tesk, March 1985.

Biological Safety Evaluation of a Newly Developed High Strength, Acrylic

Resin Compatible Adhesive Cement, C. Siew, S. Gruninger, R. Hsu, G.M.

Brauer, J.A. Tesk, March 1985. ' ' '

63
NBS-114A (rev. 2-ao

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO.

NBSIR/86—3320

2. Performing Organ. Report N 04 3. Publication Date

FEBRUARY 1986

4. TITLE AND SUBTITLE

Properties and Interactions of Oral Structures and Restorative Materials

5. AUTHOR(S) s

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

6 . PERFORMING ORGANIZATION (If joint or other than NBS, see instructions)

Venz, H Iizuka, and 0. Okuno

, J. Stansbury, W. de Rijk,

7. Contract/Grant No. NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, O.C. 20234

9. SPONSORING ORGANISATION NAME ANDCOMPLETE

National Institute of Dental Researc

8 . Type of Report & Period Covered

MD 20205

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 systems”

potentially applicable to other composite applications, e.g., durable resin matrices,

stronger more durable coupling between fillers and resins and improved reinforcement by

defining the types, compositions 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 biocorapatibility , higher

strength, greater toughness and adhesion to various substrates including enamel and

dentin. Analysis techniques include IR spectrocopy, 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

by wear and hardness measurement techniques, 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 of clinical results on wear and failure of

composites with laboratory test data via a time to failure analysis. Metrology and

analysis constitutes the underlying theme of investigation into porcelain-metal system,

casting of dental alloys and expansion of casting investments.

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

definition of measurement methods, materials property data, and standards of basi’

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 0MB Circular A-76, Revised inder

paragraph 5f ("Activities classified as Government responsibilities or ar^

intimately related to the public interest")." *

12. KEY WORDS (Six to t wel ve .entries; alphabetical order; capitalize oniy proper namesz^ind sepocote ke* words oy .sfm cakiriu i adhesion; castability; dfentaT alloys; aentai casting alloys; dental cements; aentai

composites; dental materials; dental restoratives; wear and degradation of

composites

13. AVAILABILITY

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|X I For Official Distribution. Do Not Release to NTIS

I 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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15. Price

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