NBS

PUBLICATIONS

NBSIR

NAT’L INST OF STAND & TECH

A11107 310127

85-3113

Properties and Interactions of

Oral Structures and Restorative

Materials

U S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Center for Materials Science

Polymers Division

Dental and Medical Materials

Gaithersburg, MD 20899

Annual Report for Period

October 1, 1983 thru September 30, 1984

Issued March 1 985

Interagency Agreement

Y01 -DE-30001 (formerly Y01 -DE-4001 5)

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

QC

100

,1156

85-3119

1985

c. 2

nal institute of Dental Research

>sda, iVID 20205

national BUREAU

OF STANDARDS

LIBRARY U f

NBSIR 85-3119

ft# '-*C L* PROPERTIES AND INTERACTIONS OF

ORAL STRUCTURES AND RESTORATIVE

MATERIALS

J.A. Tesk, J.M. Antonucci, G.M. Brauer, J.E. McKinney

R.W. Penn, J.W. Stansbury, and W. Wu

U S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Center for Materials Science

Polymers Division

Dental and Medical Materials

Gaithersburg, MD 20899

Annual Report for Period

October 1, 1983 thru September 30, 1984

Issued March 1985

Interagency Agreement

Y01 -DE-30001 (formerly Y01 -DE-4001 5)

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

TABLE OF CONTENTS

Page

ABSTRACT i

INTRODUCTION ................ ii

I. Synthesis and Evaluation of Dental Composites, Resins,

Cements and Adhesion ..... ......... 1

A. High Strength, Eugenol-Free Cements and

Restoratives 1

Background ........ . 1

Objective 1

Phase I 2

(la) Synthesis of vanillate monomers ...... 2

(lb) Synthesis of syr ingate esters 2

(2) Formulations of new cements and new

restoratives ..... 2

Phase II 2

(1)

Evaluation of mechanical properties and

bonding to metals 2

Phase III 6

(1) Synthesis of materials for pre-clinical

studies 6

(2) Pre-clinical studies of cements and IRM . . 6

(3) Ames Testing ..... 7

Phase IV

(1) Continued bonding studies of cements to

tooth structure 8

(2) Evaluation of sealing properties 8

(3) Examine incorporation of fluoride into

composition, study mechanical properties

and fluoride release 8
Phase V 10

(1) Pre-clinical studies on biocompatibility,

toxicity of newer vanillate and syringate

cements and IRM as appropriate 10

B. Monomers Which Expand on Polymerization

Objective . 10

Phase I 11

Synthesis of suitable monomers that expand on polymerization 11

Phase II and Phase III 13

Use of monomers synthesized in Phase I 13

C. Changes in Esthetic Properties of Dental Resins

and Aging 13

Objective . 13

Phase I 13

Determination of color changes in resin based

dental materials 13

D. Adhesion of Coatings and Restoratives to Dentin

and Enamel 14

Objective 14

Phase I 14

Prepare and evaluate the adhesion of compositions.

based on allyl 2-cyanoacrylate containing crosslinking agents and hydrophobic components ... 14

Phase II 15

Synthesize and evaluate adhesive properties of

oligomers of 2-isocyanatoethyl methacrylates

to dental tissues 15

Phase III 15

Arrangements for pre-clinical and clinical

studies as needed 15
E. Improvement of Dental Composites, Sealant and

Cement Materials 15

Objective ...................... 15

Phase I .................. 16

(1) Synthesis of monomers ........... 16

(2) Formulation of resins, composites

and cements ................ 16

(3) Halotopolymer cements based on dimer

and trimer acids. . 27

Phase II 28

(1) Develop improved coupling agents for

fillers such as dual silanization. ) .... 28

(2) Formulation of composite or cement system

with various fillers treated with coupling

agents. 29

(3) Determination of physical, chemical or mechanical properties as appropriate.

Develop new analytical techniques as required. ...... 29

Phase III 29

(1) Select systems for development toward

systems with potentially clinical

usefulness 29

(2) Determine properties of near optimum

systems 29

Phase IV. . 29

(1) Pre-clinical Testing. 29

(2) Clinical Evaluation 29

II. Wear Resistance and Related Physical Properties of Dental

Composite Restorative Materials

Background 30
A. Wear and Durability Assessment of Composite

Restoratives 31

Objective 31

Phase I 32

Effect on wear and hardness from preconditioning

in organic food simulating liquids 32

Phase II 33

Effect on wear from preconditioning in oral

environmental acids 33

Phase III 35

Diffusion, effect of fillers on the swelling

ratio in composites 35

Phase IV , . 36

Glass transition measurements 36

Phase V 37

A Composite dilatometer for measuring polymerization volume changes 37

B. Formulation of New Dental Resins to Improve Durability 38

Objective 38

C. Clinical Evaluations 40

III. Dental Alloys and Ceramics 41

Background 41

A. Porcelain-Alloy Compatibility (Thermo-mechanical

Compatibility) 42

Objective 42

Phase I 43

Determine the temperature dependence of elastic

modulus for dental porcelains and alloys .... 43
Phase II .

Finalize the ultimate computer program on the

final element model (FEM) of split ring stress . 44

Phase III .......... o ....... . . « . 44

Finalize material input parameters for split

ring computer program and fine tuning for match

with experimental results.

Phase IV 44

Devise simple analytical representation of split

ring stress-strain calculations if possible.

Phase V 44

Examine results of FEM vs 2-dimensional theory

developed by Scherer ...... . 44

Phase IV. 44

Modify expansion and other properties of porcelain and/or alloys to establish limits for

clinical stress compatibility 44

Porcelain-Alloy Compatibility (Bond Strength) .... 44

Phase I ....... 45

Determine the most appropriate method for

representing BBC data 45

Phase II 45

Determine three dimensional and two dimensional

FEM of BBC . . 45

Phase III . 45

Determine theoretical curve filling methods:

exploration of 3~parameter Weibul analysis ... 45

Phase IV 45

Photo elastic study of BBC 45
Phase V 45

Explore effects of alloy reuse, specimen reuse,

annealing of porcelain, immersion in water (or

saline solution) on system strength 45

B. Castability (Filling a Mold with Cast Dental Alloy) . 46

Objective 46

Phase I 46

Statistical and functional representation of

castability 46

Phase II 46

Multivariant analysis of effects of composition

on castability 46

Phase III 47

Extension of the method to other investments

and mesh sizes 47

Castability (Fit of Dental Castings and Investment

Expansion) 47

Objective 47

Phase I 48

Strain guages used in dental investment 48

C. Solderability 48

Objective 48

Phase I 49

Develop solderability specimen pattern, theory

and experiment 49

Phase II 50

Initiate tests 50
Phase III ..... .......... 50

Modification of testing ............ 50

Phase IV ............ 50

Evaluation of alloys and solders 50

REFERENCES 51

MANUSCRIPTS IN REVIEW OR ACCEPTED FOR PUBLICATION ....... 54

PAPERS PUBLISHED 55

INVITED TALKS 56

PAPERS PRESENTED AT THE 1984 IADR/AADR MEETING IN DALLAS. ... 57

ABSTRACTS SUBMITTED FOR 1985 IADR/AADR MEETING IN LAS VEGAS . . 58

ABSTRACT

Significant accomplishments during the FY84 are itemized as follows:

(1) Synthesis of syringate esters and of polymerizable vanillates was achieved. Properties of cement composites were determined and found to

hold potential as intermediate restorative materials. Formulations which

adhered well to porcelains, composites, and metals were developed. (2)

Preclinical evaluations of syringate and vanillate cements showed mild

pulp reactions, negative Ames tests, high LD^q (oral values and only

slight hemolysis). In general, biocompatibility was good. (3) Fluoride

containing cements were found to be adequately strong. (4) New, polymerization expanding monomers were formulated in high yields. (5) High

strength, low water absorption, fluorinated resin composites were achieved

with reduced polymerization shrinkage. (6) Dimer and trimer acid cement

formulations were discovered that expand on polymerization. (7) PETMP, a chain transfer agent was found effective in increasing the degree of cure

of dual cured (light and chemical) composite resins. (8) Wear studies

showed glass ionomer cements prone to catastrophic failure in the presence

of lactic acid. (9) Preconditioning of dental composites in acids showed

quartz and pure silica glass filled versions only slightly affected

regarding wear. Radiopaque filled composites were more strongly attacked.

(10) Experimenbts confirmed that composites swell in an inverse relationship relative to the filler content. (11) A sensitive, stable dialometer

was constructed for measuring polymerization shrinkage. (12) More highly

cured dental composites resisted clinical wear of a greater degree, except

in one instance which revealed the importance of considering polymerization shrinkage and filler content. (13) Temperature dependent elastic

properties of dental porcelains and nickel based alloys were determined.

(14) The effectiveness of Weibul statistics in distinguishing between

failure stresses of porcelain fused to metal systems was demonstrated.

(15) The first mathematical descriptiuon of the effects of elemental

composition on a castability value, C

y

, as functions of alloy mold and

casting tmeperatures was developed. (16) Preliminary studies of casting

investment setting expansion using strain gauges showed internal expar.'i:o

apparently much less than externally measured expansion.

i
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-t.o-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 of

porcelain-fused-to-metal . Special emphasis is being placed on measurement

techniques and flaw analysis.

ii
1

I . Synthesis and Evaluation of Dental Composites, Resins, Cements and

Adhesion

A. High-Strength, Eugenol-Free Adhesive Cements and Restoratives.

Background

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

[1,2]. These cements have the following advantages compared to the presently used Zinc Oxide-Eugenol (ZOE) or EBA cements: (1) they have excellent strength, (2) have much lower solubility than zinc oxide-eugenol

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

conjunction with composite filling materials to which they adhere, (4) are

compatible with acrylic monomers and can be formulated in conjunction with

them, and (5) adhere strongly, even on prolonged water exposure, to nonprecious metals and composites. The cements exceed considerably the requirements of ANSI/ADA Specification No. 30 for Type II, III, and IV type

restoratives.

Objective

The objective of this study is to continue to evaluate these cements

for various dental applications and to further improve desirable properties. To achieve this objective the following tasks were planned for

the period of this project: (1) synthesis and evaluation of divanillates

and polymerizable vanillates such as methacryloylethyl vanillate and addition of these compounds to hexyl vanillate-ethoxybenzoic acid (HV-EBA) cements to improve mechanical properties; (2) quantitative measurements of

the adhesive properties of HV-EBA cements; (3) development of intermediate

restorative formulations (IRF) incorporating monomers and reinforcing

fillers with cement ingredients and determination of their mechanical
2

properties; (4) synthesis of cements using structurally related syringate es

ters and evaluation of their physical properties and (5) guidance and assistance for studies of (a) the biocompatibility, (b) pulp irritation and

tissue response as well as for clinical studies using these cements to be

conducted at such institutions as Indiana University, Baylor, Northwestern

University, University of Tennessee and the University of South Carolina.

Progress Report

Phase I

(la) Synthesis of vanillate monomers.

A series of divanillates and polymerizable vanillates such as meth

acryloylethyl vanillate and vanillyl methacrylates were synthesized. These

compounds were incorporated successfully into dental cements and resulted in

improved properties. A manuscript describing this investigation has been

submitted to the Journal of Biomedical Materials Research.

(lb) Synthesis of Syringate esters.

These syntheses were essentially completed during the last reporting period. A paper describing this research was published in the February

1984 issue of the Journal of Dental Research (pp 137-140). A patent using

cements containing syringate esters has been applied for by NBS.

(2) Formulations of new cements and intermediate restoratives.

This work is in progress and will be presented in FY85 report.

Phase II

(1) Evaluation of mechanical properties and bonding to metals,

porcelains and composites.

(a) The evaluation of cements containing vanillate compounds with multifunctional groups or cements with syringate esters ingredients was completed.
3

(b) Additional properties of cement composites incorporating monomers and suitable polymerization accelerators in the liquid, and

silanized glass and peroxide initiator in the powder were determined.

These cement composite formulations, because of their high strength, low

solubility and strong adhesion to various substrates, appear to be most

useful as intermediate restoratives. A manuscript describing properties

of the compositions investigated has been accepted for publication in the

Journal of Dental Research.

(c) Incorporation of acids into vanillate or

syringate cements.

Further improvement of these cements was obtained by

kncorporating small concentrations of acid such as propionic acid into

these formulations. Cements with better properties were obtained by coating 2? propionic acid on some of the zinc oxide powder rather than by adding acid to the liquid portion. Addition of the propionic acid coated

powder improved working properties of the mixtures, decreased setting

times to any desired time (thus permitting control of the cement cure) and

allowed incorporation of higher concentrations of HV into chemically useful formulations. It also reduced brittleness of HV-EBA and ethylhexyl

syringate (EHS-EBA) cements. Selected properties of these cements are

given in Table 1. Dental luting agents of standard consistency with film

thickness as low as 5 uni have been obtained. Maximum film thickness for

ZOE cements is 25 um in the ADA Specification. Adhesion of these cements

to stainless steel and porcelain is excellent. Mean values for five measurements were as high as 19.2 MPa (2780 psi) for the stainless steelcement and 14.6 MPa (2120 psi) for the porcelain-cement bond. On addition

of plasticizing agents, e.g. zinc undecylate, flexible materials with po-
4

tential usefulness as tissue packs were obtained. A talk describing these

studies was presented before the International Association for Dental Research in March 1984.

(d) Improvement of cements by adding metal powders.

Metal powders such as stainless steel or titanium have been

incorporated into typical HV-EBA-ZnO formulations. The results obtained so

far do not indicate that addition of such metals will improve appreciably

the mechanical properties of the cements.

(e) Measurement of the bond strength of the cements to various

substrates.

ZOE cements and other temporary restoratives do not bond to composites or metals in an aqueous environment. The HV-EBA or HV-EHS-EBA cements as well as the "cement composites" adhered strongly to non-precious

metals, composite resins and porcelain. They formed stronger bonds to

these substrates than do ionomer cements. The joined specimens broke cohesively, often considerably above the tensile strength of the cement (Table 1). This high bond strength especially to stainless steel, may result

from the extremely low film thickness of most formulations. Porcelain-toporcelain or porcelain-to-composite specimens joined together with HV-EBAZnO cements had higher bond strength than joints prepared with commercial

bonding agents. Pretreatment of the porcelain with a commercial porcelain-acrylic resin bonding agent or roughening the porcelain surface further increased bond strength. With proper pretreatment of enamel surfaces

the adhesion of HV-EBA cements is similar to ionomer cements. The latter

materials however, have a somewhat greater bond strength to dentin.
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Phase III

(1) Synthesis of materials for pre-clinical and clinical

studies.

Vanillate and syringate esters synthesized in this laboratory

have been made available to many researchers on request. Hexyl vanillate

is now commerically available from two manufacturers of specialty chemicals.

(2) Pre-clinical studies of cements and IRM 1 .

A number of studies on various aspects of the biocompatibility of

these cements and their individual ingredients are being conducted at other

institutions. These investigations are in various stages of completion.

(a) Pulp reactions to HV-EBA cements.

This investigation by Drs. Kafrawy and Phillips at Indiana

University was reported at the 1984 IADR meeting (Abst. No. 2). It was

concluded that the mild pulp reactions in monkeys were similar to those

illicited by IRM.

(b) Mutagenicity.

Hexyl vanillate prepared in this laboratory gave a negative

spot test by the procedure of Dr. Bruce Ames with Salmonella Strains TA97,

TA98 and TA100. These tests were conducted by Drs. Miller, Washington,

Zimmerman and Bowles of Baylor University. Results were reported at the

1984 IADR meeting (Abst. No. 1278).

A mutagenicity assay was conducted for o-ethoxybenzoic acid

and also with 64$ Zn0~30$ A^O

3 - 6 $ hydrogenated rosin powder and compared

with negative and positive blanks. Using Salmonella strains TA98 and TA100 these compounds gave negative tests. The mutagenicity of HV by this

1 A commercially available Intermediate Restorative Material.
7

more time-consuming procedure is nearing completion under the direction of

Dr. C. Siew, Director of Toxicology, American Dental Association Health

Foundation.

(c) Acute Oral LD^q for ZnO-A^O^-hydrogenated rosin is >1.0

g/kg. These studies were conducted at the American Dental Association

Laboratories

.

(d) Hemolysis.

Both o-ethoxybenzoic acid and ZnO-A^O^-hydrogenated rosin

are slightly hemolytic (18. 5 ± 2.55° and 19.9 ± 2.0 respectively, ADA

Laboratories)

.

(e) Activation of complement by HV-EBA-ZnO cements.

Many foreign substances interact with the serum complement

system and complement activation is important to immunopathological

response to antigenic materials. With these thoughts in mind, work was

undertaken by Drs. Keller, Hoyt and Boackle of the University of South

Carolina to study the activation complement by HV-EBA-ZnO and other selected cements. These might interact with complement in the gingival sulcus and pulpal tissues of unlined cavity preparations. (1984 IADR, Abst.

No. 428).

(3) As soon as results of the detailed Ames tests for hexyl

vanillate become available, permission will be requested from the Human

Research Ethics Committee of the National Bureau of Standards to place a

limited number of HV-EBA-ZnO restorations in human patients.
8

Phase IV

(1) Continued bonding studies of cements to tooth structure.

Pretreatment of enamel with various acids increases the adhesion

of this substrate to HV-EBA-ZnO cement. Some typical values of the bond

strength are given in Table 2. Use of 37$ phosphoric acid is quite

effective. Such treatment is not biocompatible for dentin, but some

adhesion of the cement is obtained by pretreatment of this substrate with

either 1$ sodium citrate or aq. polyacrylic acid (see also Phase II, 2e.)

New formulations to improve the materials compositions incorporating plasticizers, metal powders, or fluorides have been prepared and

evaluated. See Phase II (2c, 2d) and Phase IV (3). Materials useful as

tissue packs containing the suggested ingredients and Crisco^ have been

prepared and evaluated at Northwestern University. These materials have a

low dimensional change.

(2) Evaluation of sealing properties.

The properties of the cements as endodontic sealers have been

measured by Dr. Glick and Dr. Greener at Northwestern University. Sealing

characteristics of these materials are better than those of a commercial

endodontic sealer. The hexyl vanillate has some irritating action similar

to eugenol, but the cement does not show a bacteriostatic zone of

inhibition.

(3) Examine incorporation of fluoride into compositions. Study

mechanical properties and fluoride release.

Incorporation of a leachable fluoride without lowering the physical properties should yield useful caries-reducing cements. HV-EBA-ZnO

and EHS-HV-EBA-ZnO materials containing sodium fluoride, zirconium fluo2 A vegetable oil product manufactured by Proctor and Gamble.
9

Table 2

EFFECT OF PRETREATMENT OF SUBSTRATE ON ADHESION TO HV-EBA CEMENTS

Powder: 64 ? ZnO - 30? A1

2 0

3 = 6 ? hyd. rosin

Liquid: 12.5? n-Hexyl Vanillate - 87.5? EBA

Cement stored in water for 24 hours

Pretreatment of Substrate Adhesion in MPa to

Enamel Dentin

None

37? H^POij

37? H

3 P 04

3

1? Na Citrate

0.1? Ferulic Acid

1.25? Ferulic Acid

1.25? Ferulic Acid

5.0? Ferulic acid

Aq. Polyacrylic Acid3

1.2 + 0.4 0.5 ± 0.2

1.8 + 0.3 -

3.5 -U 1.9 -

- 1.0 + 0

2.7 + 0.7 4 -

3.5 + 0.7 0

2.7 + 0.7 4 2.3 + 0.7 4

0.2 + 0.3 4 -

1.8 + 0.3 1.0 + 0.2

-> A cement-composite of the following composition was used:

Powder: 1 pt 64? ZnO - 30? AI 2O

3 - 6 ? hydr. rosin, 1 pt sil. glass

+ 1? Bz 2 02

Liquid: 1 pt 12.5? n-Hexyl Vanillate - 87.5? EBA, 1 pt monomer + 1? DHE?

+0.02? BHT

Stored at 100? relative humidity
10

ride or disodium monof luorophosphate were prepared and their properties

determined. Cement with 0.1 to 2.055 NaF in the powder had adequate tensile

and compressive strength and adhered well to stainless steel and composite

(for properties of selected compositions see Table 1). On storage HV-EHSEBA-ZnO cements with above 0.5$ NaF increased excessively the fluoride

concentration in water. No unusual leaching was found for cement with 0.1

NaF or 0.2$ ZrF^. The dissolution of fluoride over long periods will be

studied by means of the fluoride electrode. Cements with disodium monofluorophosphate were brittle.

Phase V

(1) Pre-clinical studies on biocompatilibity , toxicity of newer

vanillate and syringate cements and IRM as appropriate.

Samples of some of these compositions have been prepared and

distributed to interested parties. No results are available at this time.

B. Monomers Which Expand on Polymerization.

Objective

The objective of this portion of the study is to synthesize new spiro

ortho-carbonate compounds which can be polymerized by free radical initiators to give expansion upon polymerization. The physical properties of

the various homopolymers and selected copolymers will be evaluated and

correlated to the overall degree of expansion observed. Enhanced adhesion

is anticipated as a result of a zero or a positive expansion upon curing

of resin. To take advantage of this, the study is focusing on highly substituted monomers which will yield expanding polymers with high glass

transition (Tg) temperatures. Monomers will be synthesized to investigate

the effect of ring size on the mechanism of ring opening polymerization.
Progress Report

Phase I.

Synthesis of suitable monomers that expand on polymerization.

Synthesis of the monomer, 3, 3-dimethyl-9-methylene-1 , 5, 7 , 1

1 -tetraoxaspiro [5.5] undecane (Fig. 1) has been successfully accomplished. This

novel compound was selected as a model compound to work out the synthetic

difficulties encountered in preparing substituted, unsymmetrical spiro

ortho-carbonates capable of free radical ring opening. The key step in

the process involved development of a method to obtain six membered ring

thiocarbonates (Compound 1, Fig. 1) which are fairly unstable intermediates and require a very mild synthetic reaction procedure. With this technique available, the new monomer was prepared in approximately 50 % overall

yield. Polymerization studies involving various initiators and conditions

will be conducted to verify the ring opening mechanism and evaluate the

degree of expansion.

While this monomer may have interesting applications of its own, especially with its low melting point of 3^°C, this study was devised to

prepare and evaluate monomers which are precursors of high T expanding

O

polymers. Therefore, the new thiocarbonate synthesis was applied to a series of anthracene-based diols. The five membered ring anthracene-thionocarbonate adduct (Fig. 2A) was synthesized in good overall yield and the

corresponding monomer (Fig. 2B) is currently being prepared. The six membered thionocarbonate (Fig. 3A) which arises from a 1,3~diol has been obtained, but only in poor yield. This particular compound appears to be

extremely moisture-sensitive and its synthesis must be modified accordingly. A very small quantity of the desired monomer (Fig. 23) has been
1 2

Fig. 1

Fig. 2

Fig. 3 Fig. 4
13

prepared, but lack of the preceeding intermediate severely limited the

scale of the reaction. From a single attempt at forming a seven raembered

thionocarbonate (Fig. 4A), the only isolated product was a cyclic ether

(Fig. 4B) resulting from a ring contraction. The reaction will be rerun

at a lower temperature in an attempt to stabilize the desired compound.

Phases II and III await completion of Phase I. These phases involve

use of the monomers synthesized in Phase I to formulate composites and

adhesives (Phase II) and evaluate properties (Phase III).

C. Changes in Esthetic Properties of Dental Resins on Aging.

Obj ective

The objective of this part of the study is to improve esthetic

properties of dental resins and to establish causes and mechanisms of

discoloration and aging.

Progress Report

Phase I

Determination of color changes in resin based dental materials.

Study the discoloration on aging in various environments due to exposure to different energy sources. Determine color changes of dental resins, plastic teeth and composites resulting from (1) irradiation of a 150K

lux Xenon lamp under water or in air, (2) a standard RS light source used

in the ADA specification tests, (3) exposure to elevated temperatures , in

the dark in air and in water, and (4) exposure of specimens to the different environments for various periods of time.

Results during the previous period had shown that dental composites

are more sensitive to color changes due to aging from exposure to radiation than denture base resins or plastic teeth. Thus, (1) conventional
14

chemically cured, (2) chemical cured microfilled, (3) light cured, (4)

light cured microfilled and (5) light cured and chemical cured composites

were exposed to various conditions. The combined light cured and chemically cured material and some chemically cured brands showed perceptible

color changes on 24 hr irradiation by the Xenon light source. Generally,

longer irradiation did not increase the color changes. Masking of a portion of the specimen with foil improved the ability to differentiate color

changes caused by exposure to the radiation. Light cured composites were

more color stable than the chemically cured ones. Storage of the materials in the dark for a week at 60°C did not alter the color. The effect of

shade (dark or light) of composite brands on color stability is being determined. An effort is being made to delineate the causes for the color

changes on aging and to determine how to prevent them. For this reason

analysis of the composition of the composites for the amine accelerator

and any light stabilizer will be conducted.

D. Adhesion of Coatings and Restoratives to Dentin and Enamel.

Objective

The objective of this investigation is to synthesize compounds which

will improve adhesion between dental tissues and restorative materials and

to incorporate them into restorative compositions

Progress Report

Phase I.

Prepare and evaluate the adhesion of compositions based on allyl

2-cyanoacrylate containing cross-linking agents and hydrophobic components

to improve hydrolytic stability.
15

The monomer was synthesized. On storage of extended time periods

(several months) in a refrigerator, the monomer, even after addition of

inhibitor, underwent polymerization. The depolymerization of this material to regenerate monomer of suitable purity is being pursued.

Phase II.

Synthesize and evaluate adhesive properties of oligomers of

2-isocyanatoethyl methacrylates to dental tissues.

This phase now appears to yield more important results. It is being

initiated at this time, but will receive major attention during the following year.

Phase III.

If appropriate results are obtained, proceed to arrange pre-clinical

and clinical studies as needed.

No studies have been conducted on this phase.

E. Improvement of Dental Composites, Sealant and Cement Materials

1. Dental Resins for Hydrophobic Composites

Obj ective

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

Previous research has indicated that the oral environmental resistance (OER) of resin-based dental restorative, sealant and adhesive materials is a significant factor in determining their performance and

service life [3,4]. The sorption of relatively excessive amounts of wate^

as well as other chemicals present in the oral cavity can promote plasti-
16

cization of the organic matrix, and, ultimately, degradative attack not

only of the polymeric binder but also of the interfacial bonding system

and, in some cases, of the filler itself [5-8].

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 far removed from

that prevalent in the oral environment. The other is aimed at increasing

the degree of polymerization and the crosslink density of the resin systems by methods compatible with the clinical situation. The first approach involves the synthesis and formulation of resins that yield polymers containing significant amounts of fluorocarbon or siloxane segments

to result in dental materials having the desired hydrophobicity and solubility parameters to resist the detrimental effects of the oral environment. The second approach, which also may encompass the first approach,

involves the synthesis and formulation of multifunctional methacrylates,

chain transfer agents and other types of network forming agents that can

augment the degree of cure and crosslink density. Emphasis also is directed to monomers that should have minimal polymerization shrinkage. An

ancillary part of this approach also involves the development of more efficient initiator systems for ambient polymerizations of dental resins.

Progress Report

Phase I

1. Synthesis of monomers, and

2. Formulation of resins, composites and cements.

a. Formulation and Evaluation of PFMA-Based Composites

We continued our study of resin-based composites formulated

with the polyfluorinated prepolymer multifunctional methacrylate, PFMA.
17

The major achievement of this phase has been the successful development of

a highly esthetic, mechanically strong, quartz filled fluorinatea

composite. Previous PFMA based composites formulated with a conventional

barium oxide containing silanized glass were deficient in transluscency

due to the mismatch of the refractive indices of the glass filler and

fluorinated resin system. Fused quartz (refractive index = 1.4583) was

optically compatible with the following fluoro-resin system: 68. 8455 PFMA,

29.50 DMDMA5

, 0.98 % PETMP 6

, 0.40 DHPPT7, and 0.28 DMAPS8

. Using a

powder/liquid formulation, P/L = 3, composites with excellent esthetics

and having the following properties were obtained: setting time = 2.0

min., diametral tensile strength = 41 MPa, compressive strength = 232 MPa,

water sorption = 0.17 mg/cm^. The compressive strength value represents

the highest achieved thus far with a PFMA formulation.

b. Synthesis of a Polyfluorinated Prepolymer Multifunctional Urethane Methacrylate (PFUMA)

The polyfluorinated oligomeric polyol, PFA, was converted

to a multifunctional urethane type methacrylate using the difunctional

monomer isocyanatoethyl methacrylate (IEM) as outlined below (Fig. 5):

<5^DMDMA - 1 , 1 0-decamethylene dimethacrylate

°PETMP - pentaerythri tol tetra 3~mercaptopropionate)

IDHPPT - N,N-bis(2-hydroxypropyl)-p-toluidine

a DMAPE - p-N,N-dimethylaminophenethanol
18

CF CF CF —C-O-CH -CH-CH -OC-CH=CH-CH -C-OCH -CH-CH -0-

CF OH CF

3

PFA

+

CH

CF OH

N = 10

CH C-COCH CH NCO

3

II 2 2

0

I EM

CH Cl

2 2

PFA Backbone

C=0

I NH

I CH

I 2

CH

I 2

0

I c=o

I C-CH

CH

2

PFUMA

Figure 5
19

IEM via its -NCO group reacts with the -OH groups of PFA yielding a polyfluorinated prepolymer monomer, PFUMA, which contains pendant urethane and

methacrylate groups. PFUMA is a pale yellow liquid of somewhat greater

viscosity than PFMA. PFUMA also has a higher refractive index than PFMA

(1.43^7 vs 1.4197) which may make it more optically compatible with radiopaque glass fillers than PFMA. Structural confirmation by infrared and

NMR analyses has been obtained. PFUMA is miscible with many conventional

diluent monomers. Composites based on this unique fluorinated resin are

currently being formulated for evaluation.

Dental Resins for Increased Degree of Polymerization and Crosslink

Density

.

c. Synthesis of a Diurethane tetramethacrylate ( BIS-GMA/ISM)

.

The diadduct of BIS-GMA and IEM was prepared using in

CH 2Cl2 using triethyl amine (Et^N) as a catalyst (Fi 6 ):

2 IEM + BIS-GMA

CK

2C1 2* Et 3N

0 0 CH

3

BIS-GMA /I EM

C=0

CH

L 2

Figure 6.
20

BIS-GMA/IEM is an almost colorless liquid somewhat less viscous than

BIS-GMA despite its greater bulk (molecular weight = 822). Composites

based on this tetrafunctional, bulky monomer are under study.

d. Synthesis of a Siloxane Tetramethacrylate

Again from BIS-GMA, a unique tetrafunctional vinyl monomer

of great bulk was prepared using 3 -methacryloxypropoxydimethylchlorosilane (MPDMCS) as shown in Fig. 7.

f3

CHp=C-C-0-CHp-CH-CHp-0

II \ OH

BIS-GMA

(pH

3

(jJH 3 (JH 3

<jj- + 2 CH2=C-C-0-CH2CH 2CH 2-|i-Cl

CH- CHMPDMCS

CH 2Cl 2 /Et

3

N

BIS/GMA/MPS

Figure 7.
21

BIS-GMA/MPS 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 composites 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; diametral tensile strength of visible light cured composites was 42 MPa. Other properties of this unique type of composite are

under investigation.

e. Formulation and Evaluation of Composites Utilizing a

Disiloxane Diluent Monomer (BIS-MPTMS).

This task is directed at assessing the effect of the disiloxane diluent monomer Bis-(methacryloxypropyl ) tetramethyldisiloxane (BISMPTMS) on the properties of dental composites based on BIS-GMA and 3ISIPMA , 2, 2-[p-(methacryloxyisopropoxy)phenyl] propane. Table 3 summarizes

our results to date on the mechanical properites of such composites compared to typical BIS-GMA and BIS-IPMA composites (Formulations A-C). The

salient point of these results is the maintenance of the good mechanical

properites of the base resin even though significant amounts of the very

flexible disiloxane diluent are used. The use of the less viscous, highly

flexible BIS-MPTMS in place of TEGDMA also permits higher filler loadings

with BIS-GMA. This unique diluent monomer is also compatible with urethane methacrylate monomers.
22

Table 3

MECHANICAL PROPERTIES OF COMPOSITES9 USING BIS-MPTMS AS A DILUENT

Formulation Resin Composition

(in weight $)

P/L Mechanical

DTS

Strength in

CS

A BIS-GMA (70) 4 50 239

TEGDMA (30)

B BIS-IPMA (100$) 4 43 204

C BIS-IPMA (100$) 5 47 253

D BIS-GMA (80) 4 44 248

BIS-MPTMS (20)

E BIS-GMA (70) 4 48 232

BIS-MPTMS (30)

F BIS-IPMA (90) 4 42 209

BIS-MPTMS (10)

G BIS-IPMA (80) 4 45 210

BIS-MPTMS (20) 4.5 44 188

H BIS-IPMA (70) 4.5 40 200

BIS-MPTMS (30) 5.0 42 227

I BIS-IPMA (60) 5 45 210

BIS-MPTMS (40)

J BIS-IPMA (50) 6 44 -201

BIS-MPTMS (50)

^Composites were cured using visible light (Caulk Lite, L. D. Caulk,

Milford, DE) for 70 s per side. The catalyst system consisted of 0.2$

camphoroquinone and 0.7$ ethyl 4-dime thylaminobenzoate. The glass filler

was Corning Glass 7724 (3255 mesh) silanized with 0.5$ 3~methacryloxypropyltrimethoxysilane as previously described.
23

f. The Effect of a Polythiol on the Degree of Polymerization of Dental Resin Based Materials.

Final properties of dental composites such as hardness,

stength and wear are primarily related to the composition of the composite

and to the conversion of double bonds in the resin.

As described in a recent study the decrease in hardness on

composite surfaces caused by chemical softening can be diminished by about

40$ when the curing temperature was 80°C instead of 37°C [9]. Also, the

wear resistance was significantly improved due to higher degree of cure in

the resin obtainable at the higher temperature.

Several studies [10,11] describe the determination of residual unsaturation in either commerical or experimental composites or unfilled resins. Ruyter [11] used multiple internal reflection to study the

conversion of double bonds and reports remaining double bonds in commercial composites to vary between 25$ and 48$. Others [12] used Fourier

Transform Infrared Spectroscopy (FTIR) to evaluate the conversion of C=C

double bonds in several unfilled BIS-GMA resin systems using a potassium

bromide pellet sampling technique. Conversions between 52$ and 74$ were

obtained; DTS (diametral tensile strength) and unreacted double bonds are

apparently correlated for the system studied. The viscosity of the resin

system has a significant effect on the degree of conversion; of diluents

such as TEGDMA (triethylene glycol dimethacrylate) or MMA (methylmethacrylate) are used to increase the conversion of BIS-GMA.

In another investigation [12] hardness and strength a3 a

function of remaining C=C double bonds were shown to be well correlated.
24

Previous work [13] showed that adding modest amounts of

pentaerythritol tetra (3 - mercaptoproprionate) , PETMP, to experimental resins yielded cured composites with enhanced esthetics and diametral tensile

strength. This study was designed to assess quantitatively by FTIR infrared spectroscopic techniques the efficacy of PETMP as an agent for the reduction of the residual vinyl unsaturation present in cured dental resins

materials. The objectives to be addresses are:

1. Measure the degree of conversion (DC) in composite films by FTIR.

2. Measure the diametral tensile strength (DTS) for some composites.

3. Investigate factors which influence DC.

4. Determine the effect of PETMP on DC and DTS.

5. Study the correlation between DTS and DC for several resin-based

composites

.

The details of this study were presented at the 1984 IADR meeting in

Dallas and a manuscript has been prepared for publication [15]. The base

resins used in this study with their chemical structures are shown in Figure 8. A summary of the salient points of the conclusions from this study

are listed below:

1. Addition of a multifunctional chain transfer agent, such as

PETMP, in small amounts (1-5%) increased the conversion of C=C

double bonds and the strength when used with resin formulations

based on BIS-GMA, BIS-PMA or BIS-IPMA monomers.

2. The effectiveness of PETMP on the conversion is determined by

structure and stiffness of the main resin component, e.g. PETMP
25

Isomer of Bis PM A

0

ii c — HN-R-NH-C—OC

h3

=0

h2 H-CH20 -

Generalized Chemical Structure of NCO Monomer

Mol. Wt. 1000

Where R is an Aliphatic Hydrocargon Group, Oligomeric Urethane

Methacrylate Also Contains Diluent Monomer

(e.g. Triethylene Glycol Dimethacrylate)

Figure 8.
26

used with the stiff prepolymer NCO monomer is ineffective, while

when added to more flexible resins, as BIS-GMA plus diluent or

BIS-PMA, an increase in the conversion of double bonds is noted.

3. The effect of PETMP on the DTS in composites follows a very

similar pattern. Increase in stength through addition of PETMP

is shown here to be influenced by (a) structure and stiffness of

the main resin components, and (b) the number of C=C double bonds

lost (new C-C- bonds formed).

4. A positive correlation exists between conversion of C=C double

bonds and DTS (as reported by Ferracane and Asmussen) . However,

this correlation applies only within a given resin system.

g. New Initiator Systems for Resin-Based Dental Materials.

Previously we had shown that polythiols such as PETMP could

function as polymerization accelerators for chemically cured dental

resins. That is resins containing peroxides such as benzoyl peroxide or

cumene hydroperoxide and PETMP were polymerizable under ambient conditions

in clinically acceptable times [14].

We have also investigated the accelerative potential of

PETMP on camphoroquinone (CQ) . PETMP is not as effective as a photoreductant as are tertiary amines although it does act as reactive diluent as

well. However, with dual cure, two part systems, PETMP is effective in

increasing the degree of cure and diametral tensile stength [15]. The

dual cure systems consist of a conventional silanzied glass powder coated

with benzoyl peroxide and a liquid resin containing photoinitiators and

slow activators (e.g. ascorbyl palmitate, ethyl-4-dimethylaminobenzoate,
27

PETMP, etc.) for the peroxide. These systems yield composites with higher

and more unifrom degrees of cure versus depth, minimal air inhibition and

enhanced strength.

3. Halotopolymer Cements Based on Dimer and Trimer Acids.

Introduction

A novel, versatile class of dental cements, termed halatopolymer

cements, was developed from the commerically available polycarboxyl ic acids, designated dimer (DA) and trimer (TA) acids [16,17]. The divalent

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

character. All of these cements have water repellent properties due to

their large paraffin like core. Some of these cements, especially those

based on the use of calcium bases, display energy-absorbing qualities under compressive stress. These cements do not inhibit the polymerization

of resin based dental materials and in fact, can be formulated to yield

hybrid composite cements. The calcium hydroxide based cement may promote

secondary dentin formation. Further details on the properties of these

cements are contained in the abstracts and microfilmed papers presented at

IADR meeting in Dallas and the 10th Annual Meeting of the Society for

Biomaterials in Washington, DC [16,17].

Obj ective

The aim of this particular phase of our general program to

develop cements of improved durability was to evaluate new DA/Ca(0H) 9 cements having improved dimensional stability, low water solubility, enhanced mechanical strength and esthetics superior to ZOE cements but with

comparable radiopacity. Strong, esthetic cements with various degrees of
28

radiopacity were obtained using fillers such as radiopaque glass and

certain titanium and zirconium compounds. Dilatometric measurements indicate that some of these cements display volumetric expansion on setting

which suggests that these cements may result in reduced microleakage.

By proper selection of the base/filler component 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.

CatOH^) with fillers such as fumed alumina, pyrogenic silica, and various

other vitreous fillers. With magnesium base powders (e.g. MgO) less

translucent cements are formed and zinc base powders (e.g. ZnO) yield

opaque cements. By proper selection of the filler components with refractive indices that match the cement matrix and which also contain radiopaque elements (e.g. Ba, Sr) it is possible to formulate translucent,

radiopaque cements.

Phases II, III and IV

Due to the necessary concentration of efforts first on Phase I of

this section, dealing with synthesis of monomers and development of

formulations, progress has not developed to the stage of proceeding with

Phases II, III and IV. These are listed here for clarity:

Phase II:

(1) Develop improved coupling agents for fillers (such as dual

silanization. )
29

(2) Formulation of composite or cement systems with various fillers

treated with coupling agents.

(3) Determination of physical, chemical or mechanical properties as

appropriate. Develop new analytical techniques as required.

Phase III:

(1) Select systems for development toward systems with potentially

clinical usefulness.

(2) Determine properties of near optimum systems.

Phase IV:

(1) Pre-clinical Testing

(2) Clinical Evaluation
30

II . Wear Resistance and Related Physical Properties of Dental Composite

Restorative Materials.

Background

This part of the report includes the performance evaluations of

dental composite restorative materials using both in vivo and in vitro

wear testing, hardness measurements, diffusion studies, viscoelastic

measurements, and volume dilatometry. From these evaluations, guidelines

are obtained which facilitate the development of new or improved dental

composite prototypes. Some examples will be given at the end of this

section.

Damage to posterior occlusal restorations has been found to be both

chemically and physically induced [18], therefore, the general wear test

procedure that is followed is to precondition the in vitro wear specimens

in organic food simulating liquids or oral environmental acids. These

liquids or acids may damage the polymer matrix or inorganic reinforcing

filler, respectively. Chemical damage from the preconditioning will decrease both the microhardness and wear resistance. The diffusion studies

are done to assess the extent of penetration and degree of concentration

of these liquids in the composites. Because diffusion and degree of cure

are affected by the glass transition, dynamic mechanical (viscoelastic)

measurements were initiated on dental polymers. From these measurements

the glass transition temperature, T CT , and the dynamic shear modulus are

o obtained. The latter gives the rigidity below and above T_. The FTIR

O . measurements determine the degree of conversion of residual double bonds

which may be used to define the degree of cure. From volume dilatometry

the polymerization shrinkage is obtained, a quantity which is useful to
31

assess the potential for marginal integrity or leakage. The clinical

tests, involving the wear of restorations placed in partial dentures, were

cconducted to check the relevance of the in vitro tests.

Finally, the information obtained from the investigations just described is being used to determine appropriate formulations for dental composite prototypes with improved durability.

This task is divided into the following sections:

A. Wear and Durability Assessment of Composite Restoratives

Phase I. Effect on wear and hardness from preconditioning in

organic food simulating liquids.

Phase II. Effect of wear and hardness from preconditioning in

oral environmental acics.

Phase III. Diffusion rates

Phase IV. Glass transition measurements

Phase V. FTIR measurements

Phase VI. Volume dilatometry

B. Formulation of New Dental Resins to Improve Durability

C. Clinical Studies

A. Wear and Durability Assessment of Composite Restoratives

Objective

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

degradation mechanisms of dental composite restorations . The results,

when correlated with in vivo tests, facilitate the development of new

dental composite materials.
32

Progress Report

Phase I

.

Effect on wear and hardness from preconditioning in organic

food simulating liquids.

Wear measurements employing a pin and disc technique [19] on

specimens preconditioned for one week at 37°C in organic food simulating

liquids were continued in this reporting period. As recommended by the

FDA [20] the food simulating liquids have solubility parameters ranging

from 1.5 x 10

-i

* (heptane) to 4.8 x 10

-i

* m“3/2 ( Water). According to

solution theory, maximum miscibility occurs when the solubility parameters

of the two component liquids are equal. Wear and hardness measurements

were made on four commercial composites preconditioned in six food simulating liquids with solubility parameters encompassing the above range.

These were Adaptic (chemically cured - conventional filler), Profile

(chemically cured - strontium glass filled), Prisma Fil (visible light activated) and Silar (chemicaly cured, microf illed) . The wear and hardness

trends were consistent. The maximum decreases in wear resistance and

hardness occurred from preconditioning in a 75$ ethanol/25$ water solution

for which the solubility parameter is 3.15 x 10

-i

* m~ 3/2. va]_ ue

for BIS-GMA, a common dental resin, is expected to approximate this value.

This result implies that any low molecular weight food component with a

solubility parameter proximate to this one will enhance the in vivo degradation of BIS-GMA based composites.

Additional hardness measurements were obtained for 12 more commerical composites [21] preconditioned in the same food simulating liq-
33

uids. The specimens were performance rated in terms of an environmental

index which involves the integral of the hardness ratio (after and before

preconditioning) over the solubility parameter bounded over the food simulating range given above. All of the composites tested showed some influence on the hardness by these liquids.

In the course of continued studies, it was assumed that resistance to solvents and their diffusion into composites would be reduced if

the degree of cure (DC) of the matrix were increased. In order to study

the influence of the DC, cure temperatures were elvevated to several temperatures up to 80°C. A correlation was observed for which the hardness

and wear resistance increased with cure temperature, or degree of cure.

Although substantial elevation of the cure temperature of in situ placed

restorations may not be practical, the need for increasing the DC is

apparent and, presumably, can be accomplished by other means.

Phase II.

Effect on wear from preconditioning in oral environmental acids.

It has been found that silicon and combined metal ions are

leached from pulverized dental composites when stored in initially pure

water for extended periods. A considerable portion of our activity during

this reporting period was devoted to determining the influence of preconditioning dental composite specimens in water and weak acids as found in

the oral environment. Wear and hardness measurements were made on five

commercial composites preconditioned for one week at 37°C in water and

0.02 N solutions of citric, acetic, and lactic acids. The composites were

Adaptic (conventional), Adaptic Radiopaque (conventional with some bar:.-,

silicate filler), Profile (strontium glass filler), Ful-fil (visible light
34

activated) and Silar (microf illed) . Except for the first and last, these

composites employ radiopaque fillers. Preconditioning in air under the

same conditions was done to obtain a control.

The wear and hardness measurements here were not always mutually

consistent as with the organic liquid preconditioning however, some qualitative conclusions were reached. The quartz and pure silica glass filled

composites (Adaptic and Silar), were the least susceptible to this kind of

preconditioning. They seemed to be essentially unaffected by water and

only a little by the acids. The radiopaques were, for the most part, more

vulnerable and in two cases pure water produced more apparent damage than

weak acids. This behavior indicates that in pure water the environment

around the glass particles becomes alkaline from the sodium that is

leached from the glass. This alkalinity attacks the silica portion of the

glass. When acids are present the alkalinity is neutralized and the attack is, therefore, impeded [22]. Stress induced by wear accelerates the

process [23].

This investigation has been recently extended to include some

commerical ionomer cements, which harden primarily by ionic crosslinking

reactions in contrast to the free radical network formation of resin based

composites. These materials were studied because they appear to have some

potential application for Class II restorations. The Commerical materials

studied so far are Espe-Chelon, Ketac, and Ketac Fil, DeTrey-Chemf il II,

and Fuji II. For the most part these involve acrylic acid copolymers and

a calcium-alumina silicate glass. Ionic crosslinking is caused by calcium

or aluminum ions reacting with ionized carboxyl groups. According to wear

and hardness measurements, all of these materials reveal very little damage from preconditioning in water, but considerable damage is inflicted by
35

preconditioning in lactic acid. The hardness and resistance of the chemically undamaged cements was sometimes larger than that for the composites

listed in the previous paragraph. The ionomer cements, however, are very

brittle, which sometimes causes cracking and subsequent catastropic failure during wear. Although this investigation is not complete, our tentative conclusion is that the extreme brittleness and susceptibility to

lactic acid impose some serious limitations on the application of these

materials to Class II restorations.

An experimental composite using a microporous glass with immiscible lithium aluminum silicate and barium silicate phases was prepared by

the L. D. Caulk Company for wear testing. The objective was to determine

whether, or not, wear and environmental resistance would be improved by

the enhanced microscopic coupling at the polymer-glass interface obtained

by etching out the lithium phase. Comparison between specimens with

etched and unetched glasses showed that etching improved the wear resistance considerably. The results with respect to environmental resistance

are inconclusive at this time. An additional inherent characteristic of

this glass is that the thermal expansion of the lithium phase in-crystalline form is negative. Thus with proper proportions of the ingredients

the thermal expansion coefficient of the composite could be made approximate to that of enamel.

Phase III.

Diffusion, effect of fillers on the swelling ratio in composites.

Dental composites are known to degrade partially due to diffusion of foreign molecules which often cause swelling. It is well known

that the equilibrium swelling ratio of the resin within a composite is

less than that of the same materials in its neat form. The extent of the
36

suppression in the resin swelling ratio has also been found to be dependent on the filler content. The basic reason for the above observations is

that the resin at the filler-resin interfaces loses a certain amount of

freedom for expansion.

A quantitative account for the above reasoning has been advanced

for both the fiber and the particulate reinforced composites such as dental composites. Analytical solutions for both types of composites in

theta solvents (those that do not change the polymer conformations) have

been obtained. As to other solvents, the deviations in the swelling

behavior from that of the theta solvents is predicted to be merely a function of n (1-2X): where n is the molecular weight between crosslinking

points within the resins and x is the solvent resin interaction parameter.

Numerical solutions for the non-theta solvents cases have also been obtained by solving a second order nonlinear differential equation.

The experimental data from our laboratory using dental composites with different filler contents confirm the above prediction. The results provide a quantitative insight into the effect of the bonding

strength and the filler content on the oral environmental resistance of

dental composites.

Phase IV.

Glass Transition Measurements.

Glass transition temperature, T , measurements were made on BISo GMA resins using a Weisenberg Rheogoniometer . This is a rotary forced vibration device, which determines the complex shear modulus. From this Tg

may be obtained by employing a temperature scan. Although the measurements were reliable at ambient conditions, some difficulties were encoun-
37

tered at elevated temperatures. Some of the problems inherant with chemically

cured systems could be avoided by using a light cell attachment for visible light activated systems. This cell, however, is not commercially available and would have to be designed and constructed. The extent of renewed

activity will depend upon the availability of the rheogoniometer and consideration of cost of cell construction vs benefits derived.

Phase V.

A composite dilatometer for measuring polymerization volume

changes

.

One of the factors considered to be important in the application

of composite dental restorative materials as well as of certain adhesive

materials is the degree of shrinkage which occurs during polymerization.

In order to measure this shrinkage a simple mercury filled dilatometer

system was assembled. The dilatometer itself is constructed from a spherical glass joint which is ground flat and covered by a flat quartz plate.

The plate is held in place by the spring clamp normally used to assemble

the joints. The stem of the joint is bent into a "U" tube and filled with

mercury. The mercury is drawn up into the "U" tube by light vacuum and

the sample is positioned by adherence to the inside of the quartz plate.

When the vacuum is removed mercury flows down to fill the joint and surround the sample. Any trapped air leaks out between the plate and the

ground surface of the joint. The high surface tension of mercury prevents

it from leaking. Volume changes are monitored using a linear variable

differential transformer whose core is attached to a poly ( tetraf luoroethylene) slug which floats on the surface of the mercury in the "U" tute.

The system has a resolution of about 10“5 cc. This sufficient
38

to measure alloy volume contraction/ expansion of 2 to 51 with a standard

deviation of 0.156, using 150 mg samples. Primarily to test this instrument the shrinkages of three commerical composite materials were measured

at 32.5°C. The results are shown in Table 4.

Table 4. Curing Shrinkage of Several Commerical Composites

Material Shrinkage Percent S.D. No. of Samples

Espe-St 4.3 .13 3

Fulfil 3.5 .10 3

PrismaFil 3.8 .07 3

These are all light-activated materials for which one can introduce the

sample and ensure that the dilatometer is at equilibrium before starting

the polymerization which is initiated by directing visible light through

the quartz plate. The problem of introducing chemically activated materials has been approached by standardizing the time after the start of mixing when the volume measurements are begun.

B. Formulation of New Dental Resins to Improve Durability (Also see

Part I, section E; Improvement of Dental Composites, Sealant and -Cement

Materials .

)

Obj ective

The objective of this task is to formulate and produce new dental

resin prototypes for more durable composites.

Progress Report

Two guidelines to develop improved dental resins resulted from our

wear research: (1) to increase the degree of cure of the resin and (2)

to shift the solubility parameter of the polymer to values below the range

of low molecular weight food ingredients.
39

The degree of cure was increased extraorally by elevating the cure

temperature. Since this method is severely limited for in situ cured

restorations , one alternative is to appropriately modify the chemical

structure. The degree of cure of a resin by bulk free radical polymerization is limited by the glass transition of the developed polymer. Curing

will be more complete if the difference between T CT00 , the glass temperature

of a completely cured system, and T__, the glass temperature at the in -

s'- situ temperature, is small. If this difference is too small, or negative,

the cure will essentially go on to completion; however, the result will be

a rubbery polymer which is unacceptable. Accordingly, a flexible resin

chain yielding a polymer with a T CTOO of about 50-60°C is desired. That is,

o a resin system having a maximal degree of freedom, yet capable of maximal

crossing and/or chain extension, resulting in a stiff, tough polymer is

the ideal matrix.

With respect to the solubility parameter a flexible chain polymer may

be expected to have a lower cohesive energy density than one with a rigid

backbone. Accordingly, a polymer with a low solubility parameter value

may be expected to have a low T^, unless it becomes highly crosslinked

during the polymerization process. Thus it appears possible to satisfy

both criteria with a low cohesive energy polymer of high crosslinked

density.

In view of these guidelines the aforementioned (Section I) polyfluorinated and siloxane containing resin based composites are being

developed and tested.
40

C. Clinical evaluations.

In collaboration with the American Dental Association Health Foundation Research Unit, clinical tests were designed to study the influence of

degree of cure on wear resistance of composite restorations [18] This work

provided a check on the validity of the assumptions used to design the in

vitro tests discussed previously. Restorations were made from the following commerical composites: Adaptic (conventional), Profile (strontium

glass filler), Prisma Fil (visible light activated) and Silar (microfilled). The restorations were placed extraorally on the occlusal surfaces

of denture teeth in partial dentures and cured at 37 and 60 °C. After six

months of in vivo wear the restorations were ranked for changes in anatomic form using SEM. With all specimens except Silar the enhanced polymerization improved the wear resistance. The adverse effect with Silar may

be attributed to excessive polymerization shrinkage, since the polymer-

/filler ratio is larger in microfilled composites. This effect was not

observed in the in vitro wear test. The distinction reveals the necessity

of including complementary clinical tests in this kind of an evaluation

program.
41

III . Dental Alloys and Ceramics

Background

In recent years, new dental alloy and ceramic systems have been

introduced to dentistry at a rather regular rate. A need exists for a

simple method to aid in characterizing the casting behavior of the new alloys. This can be useful in defining the operating conditions for employing an alloy in a dental laboratory, for assuring consistent behavior of

alloys delivered to the market and in aiding the development of new

alloys. For this purpose a polyester mesh screen has been developed in

this laboratory for use as a casting monitor.

Among the needs for porcelain-fused-to-metal (PFM) systems, is a reliable, relevant method for characterizing the strengths of these and

other porcelain veneered system(s) (PVS). As new PVS's appear and are developed, further improvements are likely to be hindered by lack of clear

understanding of the flaws or properites leading to failure. For this

purpose, work has been proceeding on development of a 3ending Beam Composite (BBC), which can effectively and relatively rapidly develop quantitative information regarding failure stresses and flaw distributions.

In a related area stress compatibility of PVS's is a topic of concern

and interest. An accepted method for characterizing this compatibility

does not yet exist. If one is to be developed, an understanding of the

roles of various material physical properties in developing stress induced

failure needs to be delineated. Toward this end, work has been progressing on defining the stresses and strains developed in a bimaterial (porcelain veneered) split metal ring. Although it is questionable whether t

analysis itself can define compatibility, useful information might be
42

gathered which will lead to more comprehensive understanding and perhaps

the development of simple, expedient, clinically relevant methods to

evaluate compatibility.

The casting of dental alloys also affects the fit of the prosthesis.

Previous studies [24 thru 30] have aptly demonstrated, the effects of investments on fit. Before improvements in investments can be effected, it

is necessary to understand the physical processes taking place within the

investment at the site of a pattern. For this purpose, strain gauges are

being investigated as measurement devices to provide this information.

Finally, the introduction of new alloy systems requires that an

agreed-upon, reliable method to evaluate soldered joints be developed.

Such a method should involve the use of techniques employed in dental

laboratories so that a reflection of the technique on the servicability of

soldered joints may be obtained.

A. Porcelain-Alloy Compatibility (Thermo-mechanical Compatibility)

Obj ective

The objective of this part of the investigation is to explore the potential of using a porcelain veneered split substrate ring (usually metal)

as a means for determining the thermal stress compatibility between the

two (veneer and substrate). For this purpose, a finite element model

(FEM) is being developed which will use the visco-elastic properites of

porcelain, elastic properites of the substrate (metal), coefficients of

thermal expansion and temperature gradients developed upon cooling in order to calculate stresses developed upon cooling. These parameters will

be adjusted so that openings or closings of the gap will mimic those of

experimental specimens. Origins of high stresses throughout the specimens

then can be defined.
43

Progress Report

The phases of research are as follows:

Phase I

Determine the temperature dependence of elastic modulus for

dental porcelains and alloys.

Two dental porcelains, one with essentially a completely glassy

structure (Ceramco) and the other with a structure strongly crystalline in

a glassy matrix were found to have essentially the same mechanical properties: Young’s Modulus, -68-69 GPa; shear modulus, -28.5~29.5 GPa; and

Poisson’s ratio, 0.19. The Young's modulus decreased by about V% for

every 100°C increase in temperature up to 500°C. An estimate of the

microcrack density, N, was calculated to be N=3-4 x 10^ cm”3. a manuscript "Elastic Constants of Two Dental Porcelains" has been prepared and

accepted for publication in the Journal of Materials Science.

Determinations of elastic-moduli for three dental alloys were

also made. The three alloys are representative of (1) a Be containing,

multiphase alloy, (2) a non-Be containing, multiphase alloy and (3) a

non-Be containing, large-grained alloy. The results are shown in Table V:

Table V

Alloy Young's Modulus Shear Modulus Poisson's Ratio

1 171 .7 65.1 0.32

2 191 .7 75.6 0.27

3 143.6 57.8 0.24

with the dental porcelains, the modulus decrement is about -1? for

100°C increase in temperature. A manuscript "Elastic Constants of Three

Representative Nonprecious Dental Alloys at Room and Elevated Tempera*: .r

has been submitted to the J. Biomedical Materials Research. T'ni 3 phase

completed

.
44

FY 83 & 84.

Phase II

Finalize the ultimate computer program on the finite element

model (FEM) of split ring stress. In progress FY84, expected to be

completed in FY 85.

Phase III

Finalize material input parameters for split ring computer program and fine tuning for match with experimental results. Planned for FY85

Phase IV

Devise simple analytical representation of split ring stressstrain caluclations if possible, (see #5).

Phase V

Examine results of FEM vs 2-dimensional theory developed by

Scherer. FY86.

Phase VI

Modify expansion and other properties of porcelain and/or alloys

to establish limits for clinical stress compatibility. To be explored in

FY86.

Porcelain-Alloy Compatibiliby (Bond Strength)

This aspect of compatibility relates to the underlying strength of

the material components in PVS’s (porcelain veneered systems), including

the strength of the bond itself. When initiated, this project was

designed to measure PMBS (Porcelain Metal Bond Strength) however, as it

progressed it became clear that what is important is the strength of the

system as a whole and the subsequent developments related to this realization. A bending beam composite (BBC) has been developed for this purpose
45

and its underlying features and method for stress computation have been

described in previous reports. Progress, according to phases, is as follows:

Progress Report

Phase I

Determine the most appropriate method for representing BBC data

This has been done, with a two parameter Weibul Statistics plot. Essentially, this is a probability of failure, P^., at a given stress level,

vs the stress level of failure, o^; i.e. P f vs o^. This method shows sta

tistically significant differences between systems which do not reveal

such differences via application of normal distribution, two sided t test

statistics. This was accomplished in FY84. For FY85 & 86, three parameter Weibul analysis will be explored.

Phase II

Determine three dimensional and two dimensional FEM of BBC.

This phase was completed in FY83.

Phase III

Determine theoretical curve filling methods: exploration of

3-Parameter Weibul analysis. Will be pursued for FY85 & 86.

Phase IV

Photo elastic study of BBC... To be explored in FY85 & 86, 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 FY85.
46

B. Castability (Filling a Mold With Cast Dental Alloy):

Objective:

The objective of this work is to investigate effects of processing

variables on the castability value, Cy, for numerous dental alloys. (Cy

is defined as the fraction or percentage of completely cast segments of a

grid pattern). The variable, Cy, is evaluated as a function of mold and

alloy casting temperatures. A transformed value of C

y , i.e. Cvt is

employed for statistical curve fitting. A further objective is to define

the effects of temperature on the effectiveness of alloying elements in

producing complete castings. Ultimately, these data may be used for

design of new alloys.

Another aspect of casting of dental alloys involves the factors

affecting the fit (or accurate reproduction of a pattern) of dental castings. A new technique employing strain gauges is being used to investigate the internal setting expansion of dental investments.

Progress Report

Phase I

Statistical and functional representation of castability. This

has been completed for (6) nickel based alloys and reported on in previous

reports (FY82 & 83 ). One manuscript has been submitted for publication

entitled "A Technique for Characterizing the Casting Behavior of Dental

Alloys’'. Another manuscript, "Castability of Dental Alloys, Mold and

Alloy Temperature Effects", is under preparation.

Phase II

Multivariant 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 1 . The following equation was found:
47

C = K + K [Si] + K [B] + K [Cb x Sn] + K, [A1 x Be] + K [Mo x Mn]

v o 1 2 3 4 5

t

Where : = function of mold and alloy temperature

[] = 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 sould be used for obtaining the castability data. However, at

this point, the technique has been demonstrated to be a viable method for

analysis. A manuscript on this is being prepared for presentation as an

invited paper at an International Precious Metals Institute Meeting in Israel, April, 1985.

Phase III

Extension of the method to other investments and mesh sizes.

This is planned for FY85 & 86 and possibly beyond.

B. Castability (Fit of Dental Castings and Investment Expansion)

Obj ective

The objective of this work is to determine if a reliable method for

obtaining the expansion of dental invetment, intrenally and at the

locations of dental patterns, can be arrived at by using strain gauges.
48

The most common method for determining the setting expansion of a dental

investment involves making external measurements on the surface of a mass

of setting investment. This may not be representative of the effects

occurring internally and the distortions that often occur in dental

castings certainly indicate non-linear effects. The ability to determine

internal effects should aid in developments of new investments/casting

techniques aimed at eliminating non-linear effects.

Progress Report

Phase I

Preliminary studies showed that strain gauges do react to the

setting of the dental investments. Results indicate that the internal expansion of dental investments is less than that measured externally, with

external measurements showing -1$ and internal measurements -0.1$. It is

not yet clear what extent the plastic backing of the strain gauges is having on the results obtained. A paper on this topic was presented at the

1984 meeting of the IADR in Dallas, Texas.

C. Solderability

Obj ective

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. It may be stated now that it is not planned

to continue this work beyond that 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 a considered need here for

development

.
49

Phase I

Develop solderability specimen pattern, theory and experiment.

This was accomplished in a trial basis for FY84. Initially, cylindrical

specimens -2.5 mm in diameter, were soldered with a fixed size gap. These

specimens were either pulled in tension or subjected to a four-point bend

test. Either method was found to work satisfactorily, with the tension

test, preferred due to its ability to reveal central area solder defects

more easily from the raw data. At first, the bend test results were preferred; however, with proper application of Weibul statistics, each method

should be equivalent.

The breaking strengths (og) are tabulated below with standard

deviations (s) and number of specimens (n).

Og (MPa) s n

Tension 306 ±156 (6)

Flexure 770 ±289 (19)

We note that all of the specimens broke in a brittle manner with no

evidence of yielding. We might possibly attribute the higher breaking

stress observed in flexure to a non-uniform distribution of flux

inclusions with more such material concentrated near the neutral axis.
50

Phases II, III, and IV

Phase II. Initiate tests (completed).

Phase III. Modification: no further effort is planned unless some

feature of the testing, particularly germaine to dentistry, is discerned

Phase IV. Evaluation of alloys and solders is not planned, this ef

fort is being discontinued.
51

REFERENCES: [1]

. G. M. Brauer and J. W. Stansbury. Cement Containing Vanillate

Esters, EBA and Zinc Oxide, J. Dent. Res . Prog, and Abstr. of

Papers, 60th Gen. Sess, IADR, Abstr. 1377 (1982).

[2]

. G. M. Brauer, J. W. Stansbury and H. Argentar, Development of

High-Strength, Acrylic Resin-Compatible Adhesive Cements, J. Dent.

Res . 62:366-370 (1983).

[3]

. W. Wu and J. E. McKinney: Influence of Chemicals on Wear of Dental

Composites, J. Dent. Res . 61 : 1 1 80— 1

1

83 (1982).

[4]

. W. Wu and E. E. Debelius: Environmental Resistance of Dental Restorative Materials, J. Dent. Res . 63 > 199, Abstr. No. 255,

(1984).

[5]

. K.-J. Soderholm: Degradation of Glass Filler in Experimental Composites, J. Dent, Res . 60 , 1867-1875, (1981).

[6]

. K.-J. Soderholm: Leaking of Fillers in Dental Composites, J. Dent.

Res. '62, 126-130, (1983).

[7]

. K.-J. Soderholm: Hydrolytic Degradation of Dental Composites, J

.

Dent. Res . 63_, 1248-1254 (1984).

[8]

. J. E. McKinney: Influence of Acids on Wear of Composite

Restoratives, J. Dent. Res . 63 , 199, Abst. 256 (1984).

[9]

. J. E. McKinney and W. Wu: Effect of Cure on Hardness and Wear of

Three Commerical Dental Composites, J. Dent. Res. 62, 285, Abst.

1047 (1983)

.

[10]

. I. E. Ruyter and P. P. Gyorosi: An Infrared Spectroscopic 'Study of

Sealants, Scand. J. Dent. Res . 84 , 396-400 (1976).

[11]

. I. E. Ruyter and S. A. Svendsen: Remaining Methacrylate Groups in

Composite Restorative Materials, Acta, Odontol Scand. 36 , 75-82,

(1978)

.

[12]

. J. L. Ferracane and E. H. Greener: Fourier Transform Infrared

Analysis of Degree of Polymerization in Unfilled Resins - Methods

Comparison. J. Dent. Res . 63 , 1093-1095, (1984).

[13]

. E. Asmussen: Restorative Resins: Hardness and Strength vs Quantity

of Remaining Double Bonds, Scand. J. Dent. Res . £0,484-489 (1982).

[14]

. J. M. Antonucci, J. W. Stansbury, D. J. Dudderar: Dental Resin and

Initiator Systems Based on Polythiols, J. Dent. Res. 61, 270, Abst.

824 (1982)

.
52

[15] S. Venz and J. M. Antonucci: Effect of a Polythiol on the Degree

of Polymerization of Resins, J. Dent. Res. 63, 199, Abst. 257

(1984).

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

Stansbury: Non-Aqueous Polycarboxylate Cements Based on Dimer and

Trimer Acids, J. Dent. Res . 63 , 294, Abst. 394 (1984).

[17]

. J. M. Antonucci, S. Venz, D. J. Dudderar, M. C. Pham and J. W.

Stansbury: Energy-Absorbing, Hydrophobic Dental Cements Based on Dimer and trimer Acids, Second world Congress on Biomaterials, 10th

Annual Meeting of the Society for Biomaterials, Transactions, VII,

137 (1984).

[18]

. W. Wu, E. E. Toth, J. F. Moffa, and J. A. Ellison, Subsurface

Damage of In Vivo Worn Dental Composite Restorations: J. Dent.

Res ., 63 675-680 (1984).

[19]

. J. E. McKinney, Apparatus for Measuring Wear of Dental Restorative

Materials, Wear 76, 337-347 (1982).

[20]

. FDA Guidelines for Chemistry and Technology Requirements of

Indirect Additive Petitions, March 1976.

[21]

. W. Wu and E. E. Debelius, Environmental Resistance of Dental

Restorative Composites, IADR-AADR Abstract 255, 62nd General

Session, Dallas, TX, March 1984.

[22]

. D. E. Clark; Carlo G. Pantano, Jr.; and Larry L. Hench, Corrosion

of Glass, Magazines for Industry, Inc., 1979.

[23]

. R. J. Charles, Static Fatigue of Glass, I., Appl. Phys . 29 , 1549-1553.

[24]

. W. G. DeRijk, M. L. Conner, K. A. Jennings, and W. Wu, IirVivo Wear

Resistance of Dental Composites with Enhanced Polymerization:

IADR-AADR Abstract 951, 62nd General Session, Dallas, TX, March

1984.

[25]

. R. W. Hinman, J. A. Tesk, E. E. Parry and G. T. Eden, Accepted for

publication in the Journal of Prosthetic Dentistry.

[26]

. G. T. Eden, 0. M. Franklin, J. M. Powell, Y.Ohta, and G. Dickson,

Fit Of Porcelain Fused-to-Metal Crown and Bridge Castings,

J. Dent. Res . ,58(12), 2360 -2368 , (1979).

[27]

. G. M. Hollenback, Science and Technique of the Cast REstoration,

St. Louis, 1964, The C. M. Mosby Co.

[28]

. R. W. Phillips, Skinner's Science of Dental Materials,

Philadelphia, 1973. W. B. Sanders Co.

[29]

. R. J. Schnell, et al . An Evaluation of Phsophate Bonded Investments

Used with a High-Fusing Gold Alloy, J. Prosthetic Dentistry 13(21),

324-335, (1963).
53

[30]

. K. Asgar, et al. Further Investigations into the Nature of

Hygroscopic Expansion of Dental Casting Investments. J. Prosthetic

Dentistry , 8(4), 673~684, (1958).

[31]

. F. Marsaw, W. G. DeRijk, et al. Internal Voljumetric Expansions of

Casting Investments, J. Prosthetic Dentistry, 52(3). 361

366 .
MANUSCRIPTS IN REVIEW OR ACCEPTED FOR PUBLICATION

Physical Metallurgy of Dental Casting Alloys, Part C, Cr-Co-Mo System;

D, Ni-Cr System; E, Fe and Austenitic Stainless Steel; and F, Titanium

Alloys. J. A. Tesk and R. M. Waterstrat, accepted for publication in

Encyclopedia of Materials Science and Engineering, to be published in

March 1985.

Fit of Multiple Unit Fixed Partial Denture Castings, R. W. Hinman,

J. A. Tesk, E. E. Parry and G. T. Eden. Accepted for publication in

Journal of Prosthetic Dentistry. '

A Technique for Characterizing Casting Behavior of Dental Alloys, (Title

changed from A Practical Method for Evaluating the Castability of Dental

Alloys). R. W. Hinman, J. A. Tesk, R. P. Whitlock, E. E. Parry anbd J. S.

Durkowski, submitted to J. Dental Research.

Elastic Constants of Two Dental Porcelains, H. R. Kase, E. D. Case and

J. A. Tesk. Accepted for publication in J. Materials Science.

Elastic Constants of Three Representative Non-Precious Dental Alloys,

H. R. Kase, J. A. Tesk, Submitted to J. Biomedical Materials Research.

Discoloration of Dental Cements and Composites in a Sulfide Solution,

J. M. Antonucci, A. Sugawara, M. Ohashi , and G. C. Paff enbarger , Submitted

to J. of Biomedical Materials Research.

Biocompatible Cementitious Compositions, G. M. Brauer and J. W. Stansbury,

patent applied for.

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

G. M. Brauer and J. W. Stansbury. Accepted for publication in J. Dent.

Res

.

Divanillates and Polymerizable Vanillates and Ingredients as Ingredients

of Dental Cements. J. W. Stansbury and G. M. Brauer, submitted for

publication in J. Biomedical Materials Research.

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

Accepted for publication in Encyclopaedia of Polymer Science and

Engineering

Chemical Softening and Wear of Composite Restoratives, J.E. McKinney and

W. Wu, Submitted to J. Dent. Res.

Environmental Damage and Wear of Dental Composite Restorations.

J. E. McKinney, Proc. Int. Symp. on Posterior Composites, St. Maarten,

Netherlands Antilles, Jan. 1985, Submitted to WERB.
PAPERS PUBLISHED

Cements Containing Syringic Acid Esters-o-Ethoxybenzoic Acid and Zinc

Oxide, G. M. Brauer and J. W. Stansbury, J. Dent. Res., 63 , 137-140

(1984).

Accelerators and Acrylic Monomer Ingredients on the Properties of Bone Cement. G. M. Brauer and J. W. Stansbury, Proc. 1st Medical Plastics Conference, The Society of The Plastics Industry, Inc., New Brunswick, NJ,

Oct. 1983.

Base Metal Alloys in Restorative Dentistry, R. W. Hinman and J. A. Tesk,

in Advanced Restorative Dentistry, L. L. Baum and R. McCoy, editors, Chap.

17, p28l-294, W. B. Saunders Company, Philadelphia, PA.

Low Surface Energy Dental Composites from a Polyfluorinated Prepolymer

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

D. J. Dudderar, Proce. 1st Medical Plastics Conference, The Society of the

Plastics Industry, Inc., New Brunswick, NJ, Oct. 1983.

Subsurface Damage Layer of In Vivo Worn Dental Composite Restorations, W.

Wu, E. E. Toth, J. F. Moffa and J. A. Ellison, J. Dent. Res., 63(5), May

1984.

Wear Mechanisms of Dental Composite Resins, W. Wu, Proc. of International

Symposium on Posterior Composites, Chapel Hill, NC, Oct. 1982, ed.

D. F. Taylor, 1984, pi 27-1 46.
56

INVITED TALKS

The Effect of Inhibitors, Accelerators , Cross-linking Agents and Monomers

on the Properties of Acrylic Resins. G. M. Brauer, Howmedica, Groton, CT

A Technique for Characterizing the Castability of Dental Alloys, J. A.

Tesk, Northwestern University, Chicago, IL. February 1984.

The Promise of the Future in Dental Materials, J. A. Tesk, Johns Hopkins

University, Baltimore, MD, January 1984

Characterization of Porcelain Fused-to-Metal Systems, J. A. Tesk, Tokyo

Medical and Dental University, Tokyo, Japan, November 1983.

Low Surface Energy Dental Composites from a Polyfluorinated Prepolymer

Multifunctional Methacrylate, First Annual Medical Plastics Conference of

the Society of Plastic Industries, Inc., New Brunswick, NJ, Oct. 1983.

A Quantitative/Expedient Porcelain Fused-to-Metal Bond Test: Theoretical

Basis and Experimental Basis, J. A. Tesk, Northwestern University,

Chicago, IL, November 1983.

The Positive Impact of Investment in R&D for the Dental Industry at the

University Level, the Government Level and the Corporate Level, J. A.

Tesk, Dental Manufacturers of America, Hyannis, MA, July 1984.

Wear Mechanisms of Dental Composite Restoratives, J. E. McKinney,

University of Maryland Dental School, Baltimore, MD, April 1984.

In Vitro and In Vivo Wear Mechanisms of Dental Composites and Simulation

of In_ Vivo Wear, J. E. McKinney, University of Maryland Dental School,

Baltimore, MD, April 1984.
57

PAPERS PRESENTED AT THE 1984 IADR/AADR MEETING IN DALLAS

A Performance Indicator for Partial Dentures, J. A. Tesk and W. DeRijk.

Environmental Resistance of Dental Restorative Composites, W. Wu and

E. E. Debelius.

Bonding of Vanillate and Syringate Cements to Various Substrates,

J. W. Stansbury and G. M. Brauer.

Influence of Acids on Wear of Composite Restoratives, J. E. McKinney.

Castability, C , of Nonprecious Alloys as a Function of Composition,

H. R. Kase, S. Hirano, J. A. Tesk and T. P. Hoepfner.

Elastic Constants of Nonprecious Alloys at Room and Elevated Temperatures

,

H. R. Kase and J. A. Tesk.

Modification of Cements Containing Vanillate or Syringate Esters,

G. M. Brauer and J. W. Stansbury.

Effect of a Polythiol on the Degree of Polymerization of Resins, S. Venz,

and J. M. Antonucci

.

Non-Aqueous Polycarboxylate Cements Based on Dimer and Trimer Acids,

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

Internal Setting Expansion of a Dental Casting Investment Measured with

Strain Gauges, E. T. Meiser, W. G. deRijk, J. A. Tesk, R. W. Hinman, and

R. Hesby.
58

ABSTRACTS SUBMITTED FOR 1985 IADR/AADR MEETING IN LAS VEGAS

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

C. C. Yu.

An Improved Dilatometer for Measuring Polymerization Volume Changes,

R. W. Penn.

Evaluation of Siloxane-Containing Dental Composites, J. S. Kuo, J. M.

Antonucci and W. Wu.

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

and J. A. Tesk.

Esthetic, Non-Brittle Dental Cements Based on Dimer Acid, D. J. Dudderar.

Properties of Vanillate and Syringate Cements Containing Various

Fluorides, J. W. Stansbury and G. M. Brauer.

Color Changes of Composites on Exposure to Various Energy Sources,

G. M. Brauer and J. W. Stansbury.

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

and N. W. Rupp.

Synthesis of a Polyfluorinated Prepolymer Multifunctional Urethane

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

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.
n c U.S OEPT. OP COMM. 1. PUBLICATION OR 2. Performing Organ. Report No. 3. Publication Date BIBLIOGRAPHIC DATA

REPORT NO.

SHEET (See instructions) NBSIR 85-3119 March 1985

4. TITLE AND SUBTITLE

Properties and Interactions of Oral Structures and Restorative Materials

5. AUTHOR(S)

J. A. Tesk, J. M. Antonucci, G. M. Brauer, J. E. McKinney, R. W, Penn, J. W,

and W. Wu

Stansbury/

6. PERFORMING ORGANIZATION (If joint or other than NBS. see instruction s) NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No. 2Y01-DE-30001

8 . Type of Report & Period Covered

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State. ZIP)

National Institute of Dental Research, NIH, DHHS , Bethesda, MD 20205

ABSTRACT: Significant accomplishments during the FY84 are itemized as follows:

(1) Synthesis of syringate esters and of polymerizable vanillates was achieved. Properties of cement composites were determined and found to hold potential as intermediate

restorative materials. Formulations which adhered well to porcelains, composites, and

netals were developed, (2) Preclinical evaluations of syringate and vanillate cements

showed mild pulp reactions, negative Ames tests, high LD sn (oral values and only slight

hemolysis. In general, biocompatibility was good. (3) Fluoride containing cements were

found to be adequately strong. (4) New, expanding polymerization expanding monomers were

formulated in high yields. (5) High strength, low water absorption, fluorinated resin

composites were achieved with reduced polymerization shrinkage. (6) Dimer and trimer

acid cement formulations were discovered that expand on polymerization. (7) PETMP, a chain transfer agent was found effective in increasing the degree of cure of dual cured

(light and chemical) composite resins. (8) Wear studies showed glass ionomer cements

prone to catastrophic failure in the presence of lactic acid. (9) Preconditioning of

dental composites in acids showed quartz and pure silica glass filled versions only

slightly affected regarding wear. Radiopaque filled composites were more strongly

attacked. (10) Experiments confirmed that composites swell in an inverse relationship

relative to the filler content. (11) A sensitive, stable dialometer was constructed for

measuring polymerization shrinkage. (12) More highly cured dental composites resisted

clinical wear of a greater degree, except in one instance which revealed the importance

lof considering polymerization shrinkage and filler content. (13) Temperature dependent

elastic properties of dental porcelains and nickel based alloys were determined. (14)

The effectiveness of Weibul statistics in distinguishing between failure stresses of

porcelain-fused to metal systems was demonstrated. (15) The first mathematical description of the effects of elemental composition on a castability value, Cv, as functions of alloy mold and casting temperatures was developed. (16) Preliminary

studies of casting investment setting expansion using strain gauges showed internal

expansion apparently much less than externally measured expansion.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon

Castability; dental alloys; dental casting alloys, dental cements; dental composites;

-dental materials; dental restoratives, wear; wear and degradation of composites.

]3. AVAILABILITY

kxl Unlimited

I I For Official Distribution. Do Not Release to NTIS

I I Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402.

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14. NO. OF

PRINTED PAGES

69

15. Price

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