NATIONAL BUREAU OF STANDARDS REPORT

10 533

Progress Report

on DENTAL CEMENTS, DIRECT FILLING RESINS, COMPOSITE

AND ADHESIVE RESTORATIVE MATERIALS: A RESUME

<nb|>

II.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT

31 1.05-1 1-3 11056 1 Fe bruary 2, 197

1

NBS REPORT

10 533

P rogress Repo rt

on DENTAL CEMENTS, DIRECT FILLING RESINS, COMPOSITE

AND ADHESIVE RESTORATIVE MATERIALS: A RESUME

G. C. Paffenbarger, D.D.S.*

* Sen io r Research Emeritus, American Dental

Association Research Unit, National Bureau

of Standards, Washington, D. C. 20234.

This investigation was supported in part by research grant

D E —027 42 to the American Dental Association from the

National Institute of Dental Research and is part of the dental research program conducted by the National Bureau

of Standards, in cooperation with the Council on Dental

Research of the American Dental Association; the United

States Medical Research and Development Command; the

Dental Sciences Division of the School of Aerospace

Medicine, USAF; the National Institute of Dental Research

and the Veterans Administration.

IMPORTANT NOTICE NATIONAL BUREAU OF ST

for use within the Government,

and review. For this reason, thf whole or in part, is not author Bureau of Standards, Washingtc

the Report has been specifically

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST) on October 9, 2015.

;s accounting documents intended

subjected to additional evaluation

listing of this Report, either in

i Office of the Director, National

y the Government agency for which

opies for its own use. <NBS>

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

Dental Cements, Direct Filling Resins,

Composite and Adhesive Restorative Materials: A Resumcf

*

Presented by

George C. Paffenbarger , D.D.S.

Senior Research Associate Emeritus

American Dental Association Research Program

National Bureau of Standards

Washington, D. C. 20234

Before the

Engineering Foundation Research Conference on

"Engineering in Medicine-Broceramics"

August 3-7, 1970

New England College, Henniker, New Hampshire

* To be published in the Journal of Biomedical Materials Research and as a hardbound book by Wiley-Inter science

.

Certain commercial materials and equipment are identified

in this paper in order to specify adequately the experimental procedure. In no case does such identification

imply recommendation or endorsement by the National

Bureau of Standards nor does it imply that the material

or equipment identified is necessarily the best available for this purpose.

(i)

Dental Cements, Direct Filling Resins,

Composite and Adhesive Restorative Materials : A Resume

Synopsis: This resume concerns: (1) experimental and

commercial dental cements and restorative and adhesive

materials usually containing nonmetallic inorganic

components; (2) the bio compatibility of (1) with

oral tissues; (3) proposed methods of bioevaluation;

(4) the oral environment; (5) the nature of the hard

tooth tissue; (6) cavity treatment; (7) agents for

bonding the restorative material to the tooth; and

(8) 112 references.

The cements include those based on: (C-l) zinc

oxide-eugenol with additives such as zinc acetate,

rosin, polymers and most important o-ethoxybenzoic

acid (EBA) ; (C-2) metallic oxides-phosphoric acid;

(C-3 ) acid phosphate salts-water ; (C-4) aluminosilicate

glass-phosphoric acid; (C-5) zinc oxide-polyacrylic acid;

(C-6) methyl methacrylate-poly (methyl methacrylate) with

or without inorganic fillers. Direct filling resins

(C-6) without filler and composite restorative materials

(C-6) with filler are based on acrylic resins or reaction
(ii)

products of acrylic (methacrylaces) with other resins.

Coupling agents include cyanoacrylates , epoxy-acrylic

adducts and polyurethanes. The 10 tables give composition t values for pertinent physical properties or

dental requirements. (C-2) dominates the cements but

(C— 1 ) with (EBA) and (C-5) which has some adhesion

to hard tooth tissues and stainless steel may displace

(C-2) . (C-4) restorative materials are anticariogenic

and widely used but are being supplanted by composite

restorative materials.

i
Cements

Cements developed for special purposes are extensively

used in dentistry as filling materials, luting media,

obtundent dressings, impression pastes and as a base for

other restorative materials

.

Current dental cements usually consist of a powder or

paste that is mixed with a paste or liquid. The resultant

mixture passes through a plastic manipulative state, which

is probably colloidal, and has a cc 'inuing increase in

viscosity until it finally solidifies.

Currently used cements include: (1) zinc oxide-eugenol

and modifications thereof; (2) phosphoric acid liquid mixed

with a variety of metal oxides or mixtures of them including

zinc oxide, magnesium oxide, cupric oxide, cuprous oxide,

manganese oxide, and/or with a complex, alkaline, aluminosilicate glass, or acid phosphate salts mixed with water;

(3) resin cements based on acrylic monomers and polymers;

and (4) a new cement with a modified zinc oxide powder

and a polyacrylic acid liquid.

Zinc oxide-eugenol cement (ZOE) . About a century ago one

of the currently used cements consisting of powdered zinc
- 2-

oxide mixed with eugenol was used in dentistry. The set

cement is a complex solid consisting of particles of zinc

oxide bound together by zinc eugenolate and of eugenol

which is sorbed by both the zinc oxide and the zinc

eugenolate .

l

“' The hardening time of an unmodified zinc

oxide- eugenol cement is very long,, usually several days,

if moisture is absent.

Perhaps the first important additive was small amounts

of zinc acetate which accelerated the reaction. Later,

hydrogenated rosin was added to increase strength and

decrease brittleness. Polystyrene and poly (methyl methacrylate) have a similar effect. . Because of

low strength, poor abrasion resistance and disintegration

in the mouth, a search was made for other metal oxides

and chelating agents that would improve the values for

the foregoing pertinent physical properties. One of these

investigations recommended a solution of eugenol and

o- e thoxybenzoi c acid (E'BA) , which when mixed with powdered

zinc oxide, had a short setting time and a marked increase

in compressive strength and, unfortunately, in water solubility. Powdered quartz and alumina

^ ^ additions

further enhanced the quality.
- 3 -

A comprehensive review of zinc oxide-eugenol type

cements with an extensive bibliography is available

.

v ‘ ;

•

There are now commercially available modified zinc

oxide-eugenol cements with characteristics which some users

believe are suitable for permanent cementation of restorations

in the mouth, but until solid clinical evidence is available,

caution is advised because of their water solubility. These

cements have obtundent properties and have little or no

irritating effect on the pulp. The biologic acceptance of

zinc oxide-eugenol based cements is the best available and

has become almost a standard for comparing the effects of

other cements

.

Table 1 shows the composition and proportions of

powder and liquid with values for a few pertinent physical

properties of certain zinc oxide and eugenol-based cements.

The table cannot be used for direct comparisons of the

effect of additives because of the many variables not only

in the substances used in compounding the cements but also

in the test procedures, especially the proportions of powder

and liquid. The table does give some idea of the range of

highest values for compressive strength encountered in

Zinc

Oxide

Eugenol

Based

Cements:

Composition

and

Properties

w

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'O -P TO ro 4-1 TS -p •P TJ ro •H 0) •H c QJ •H 0) •H QJ Z c

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u u u p 0 u u •rH u O -P o o £ u U 1 c c c 'O p C \ c rH 3 Q rH c c o T3

•rH •rH •H >1 •H •rH •H •H •H -H •H >i 1 CSJ N CSj w N

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kgf/cm

2

=

14.223

psi
-4-

existing and experimental cements having a zinc oxideeugenol base. Most of the values were obtained by test

methods, or variations thereof, given in American Dental

Association Specification No. 8 for Dental Zinc Phosphate

(9) Cement

.

Current research is centered on developing highstrength, low- solubility cements with good bioacceptance

not only for temporary filling materials, but more

importantly, for cementing media.

Zinc Phosphate Cements . Dental cements based upon a phosphoric acid liquid have been used in dentistry for at

least a century and a half. The most important one is

zinc phosphate cement in which powdered sintered zinc

oxide and magnesium oxide (usually 9:1 ratio) is mixed

with a phosphoric acid solution buffered by aluminum or

zinc salts and sometimes by booh. These cements are often

improperly referred to as oxyphosphate of zinc cements but

they contain no oxy-salts.

The set cement consists of unreacted cores of powder

particles bound together with a matrix of the phosphates of
-5-

zinc, magnesium and aluminum. Prior to unis hardened

state the mixed but not completely sec moment is in a

plastic doughy state which seme investigators believe

is colloidcl 1 .

Crowell showed .that ZnllPG^ -3ih c was the

principal crystalline phase in the set cement and that the

desirable plasticity of mixed but unset cement was caused

by ZnHP04 *3H2 G being formed in the cement liquid during

mixing

.

The requirements of the first revision (1333-1967) ^ x

( y j and the current revision (1968) of A .D. A. Specification

No. 8 for Dental Zinc Phosphate Cement and properties of

(12) dental zinc phosphate cements on the List of Certified

Dental Materials as established by the American Dental

(13) Association ana some later values are given in Tabre 2.

Although there have not been any significant improvements in zinc phosphate cements since early in this century

,

nothing has been able to displace oheir use because nothing

better has been developed for a sufficient time to determine

the long-time clinical behavior. Lt may be that the improved
- 6-

zinc oxide-eugenol or the new zinc oxide-polyacrylic

acid type cements will displace zinc phosphate cements

but it takes time to displace old materials unless there

are gross and dramatic improvements in clinical performance in the new ones

.

In Japan water- settable zinc phosphate cements were

developed in which the powder contained not only zinc'

oxide but also phosphate salts, some of which were acidic.

(17) The liquid was water. The powder of one consisted

of zinc oxide, monozinc phosphate and tertiary zinc

( 18 ) while others contained monocalcium and

(16,19)

phosphate

monomanganese phosphates

-The properties of these "water-settable" zinc phosphates have been determined by several investigators.

Data from two are given m Table 2.

The water- settable phosphate cements cannot compete

with the customary zinc phosphate cements because the

acid phosphate salts are too hygroscopic resulting in

poor keeping qualities

.
Table 2 Zinc Phosphate Cements : Composition and Properties

Zinc Phosphate Cements

(9)

Requirements of revised ADA Specification No. 8 for Dental

Zinc Phosphate Cements

(1968- )*

Arsenic Content Consistency of Mix

Time of setting

Maximum film thickness

Compressive

strength

(minimum - 24 hours)

t

Solubility and disintegration

(maximum - 24 hours)

Min. Max

.

Maximum percentage by weight

0.0002

Grams of powder in 0.5 ml of liquid

to produce a disk

30 ± 1 mm in diameter

minutes

5

minutes

9

Type Type

1 2 kgf/cm3

700

% by weight

pm pm 0.2

25 40 Requirements of 0-1) former ADA Specification No. 8 for Dental

Zinc Phosphate Cement

(1938-1967)

0.0002 Same 4 10 40

(Minimum -

7 days) 840

(Maximum -

7 days) 0.30

(12,13) Range of values for zinc phosphate cements

on List of Certified

Dental Materials (1958)

<0.0002 1.3 ± 0.3

(1.2 ± 0.1)**

7 ± 1

(8 ± 1)**

30 ± 10 1180 ± 280 0.1 ± 0.1

(25)** (0.1 ± 0.0)**

**

( 28±2

)

(840 ± 50)**

Composition (14) Percentage by weight Disk was

34 ± 1 mm in diameter

1.00

9 17 950 0.14

Powder

ZnO 89.5 MgO 9 .

4

BaCrO* 0.8

Liquid

PO* 57.9

A1 2.8

Mg 0.3

I

Water-settable zinc phosphate cement

(15) New Calmix

(Sankin Chemical Industry Co., Ltd.

(Tokyo, Japan)

1.6 8j 75 670 0.4

Powder (16) Monomanganese

phosphate (coated with

zinc hydroxide)

Zinc oxide

Liquid

Water ... 5J 31 850 0.36

Zinc oxide Monomanganese phosphate

dehydrated 240 °C for

50 minutes Water — 2ll 1250 0.34 Zinc oxide Monomanganese phosphate

dehydrated 250 °C for

50 minutes Tertiary zinc phosphate

Water — ei 28 1100 0.08

The same as Federation Dentaire Internationale (FDI) Specification No. 6 for Dental Zinc Phosphate Cement. Internat. Dent. J. 13:138 March 1963 and International Organization for Standardization (ISO) Draft

ISO Recommendation No. 1566. Dental Zinc Phosphate Cement.

** Range of unreported values for six zinc phosphate cements currently in use. Data from American Dental Association Council on Dental Materials and Devices, Chicago, 111.

+ 1 kgf/cm3 = 14.223 psi.

(o «

-7-

Copper Phosphate Cements . The copper phosphate cements are

being used less and less because they irritate the pulp

tissue more than the zinc phosphate and zinc oxide-eugenol

cements. In addition, the black copper cement is many

times more soluble in water than is zinc phosphate cement.

Data from the most extensive investigation of the

properties of these cements are given in Table 3. The

values were derived by the methods described in the A.D.A.

Specification No. 8 for Dental Zinc Phosphate Cement-

( 21 ) First Revision (1938)

.

(23

)

Zinc Polyacrylate Cements . An entirely new cement'1 ' is

A being found useful . It is appropriately called zinc polyacrylate cement but has been called zinc carboxylate cement

It is made by adding zinc oxide to an aqueous solution of

polyacrylic acid using the conventional hand mixing method.

One of the special features of the experimental cement

(23) is its ability to adhere to tooth .enamel and dentin

(25) (Table 4) and to stainless steel.

The cement is patented through the National Research

(23) and Development Corporation in the United Kingdom. Two

commercial products are available (March 197.0) —Durelon,
Copper

Phosphate

Cements;

Composition

and

Properties

CN
Table 4 Zinc Polyacrylate Cements

(Liquid-aqueous solution of polycarboxylate acid. Powder essentially zinc oxide

Material Powder/Liquid

Ratio

Adhesive

strength Compressive

strength * Tensile

strength

(diametral)

Water

uptake Dimensional

change

(linear)

Solu- Enamel* bility Dentin*

(23) Experimental

Lining 1

2 :1

kgf/cma

(A) 150

kgf/cm3

(A) 50

kgf/cm'- 1200 kgf/cm3 140 %

by weight

% % by

weight

Lininq 2 910 105 Cementing 670 64

(26) Experimental

Cementing

2 :1.

85 78-87

5745

3 :

1

79 Poly-C (24) Lining

(by weight)

1 :50

(D)

(B) (C) 0 to 22

(M) 460(G) (L) 56-79(D) 3.0 ) (R)

(D) (J) + 0.8 Lininq 1 : 43 537 (N) (0) (H) 32-34

0.8 (V) Cementinq 1 : 92 372 (P) 2.3 S D > < s > + 0.5

(D)(J) 0.4 (V) Cementing 1 :38 452 (p)

Durelon 1:4 to 1:6

11 to 98

(B) (C)(D) 0 to 61

(E)

(K) 143 - 499

(F) 46-64(D) (Q) 5.2 - 7.2

(D) (J) + 4.2

Durelon** 1.3 - 1.4 $ 0.6 (V) DeTrey's (24) Zinc Phosphate

Cement

2:5 to 3:48

(B) 0

(D) 702-1075

(i) 54-62(T) 0.9

(V) 0.3

* 1 kgf/cm3 = 14.223 psi

** Samples obtained from manufacturer's improved batches.

(A) Values converted from lb/ina to kgf/cma and rounded off.

(B) If the assembly fell apart in handling a zero value is given.

(C) Teeth stored in 70% alcohol for some months before being used.

(D) Powder/liquid ratio not given.

(E) Teeth were freshly extracted (1-3 days)

.

(F) Powder/liquid ratio 1.5:1

(G) Powder/liquid ratio 1.6:1.

(H) Powder/liquid ratio 1.9:1.

(I) Powder/liquid ratio 3 :1 - Specimens 3 to 64 hours old.

(J) Calculated from author's data. Specimens were 3 weeks in water.

(K) When Durelon was immersed in water for 28 days, the compressive strength decreased from 450 to 162 kgf/cma

. (L) Specimens 20 hours old.

(M) Specimens 4 hours old.

(N) Specimen 64 hours old.

(O) When cement specimens were stored in water for 28 days compressive

strength was 380 kgf/cma

. Powder/liquid ratio was not given.

(P) When cement specimens were stored in water for 28 days, compressive

strength was 470 kgf/cm3

. Powder/liquid ratio not given.

(Q) Specimens immersed in water from 180 to 288 hours. At 2000 hours the value was about 12 per cent and equilibrium had not been established.

(R) Specimens immersed in water for 117 hours. At 2000 hours the value

was about 6.5% with equilibrium having been established after about

250 hours of immersion.

(S) Specimens immersed in water for 166 hours. At 2000 hours the value was about 4.5% with apparent equilibrium having been established

after about 250 hours of immersion.

(T) Specimens immersed in water for 800 hours with apparent equilibrium

having been established after about 400 hours of immersion.

(U) Specimens immersed in water for 163-164 hours. At 400 hours the value was about 2%. Equilibrium was not established. Projection of the curve

of water uptake with time would give values for about 2.5% at 600 hours

and about 3.8% at 1000 hours.

(V) Solubility at 600 hours in water.
“ 8-

made by Espe, GmbH, Secfeld/oberbay, Germany (USA distributor

,

Premier Dental Products, Philadelphia, Pa. 1S107) and deTrey ®s Poly-C, made by Amalgamated Dental Co., Ltd., of

the United Kingdom (USA distributor, Cladius Ash, Inc.,

655- 73rd Street, Niagara Falls, N. Y. 14304) . In the advertisements for deTrey 1 s Poly-C no mention is made of adhesion

to the hard tooth tissues or to stainless steel. However,

the Durelon advertisement states "long-lasting adhesion to

(24) tooth structure". Two investigators v

. determined the

degree of adhesion and gave values for other properties of

the two foregoing trade brands of zinc polyacrylate cements

and of a zinc phosphate cement (deTrey 1 s) . They gave values

of adhesion from 0 to as high as 98 kgf/cm3 (0-1390 psi)

.

The scatter of values in most types of adhesion tests is

very great and these are no exception. Then, too, different

types of tests for adhesion may give radically different

values

.

Naturally, if one had a material which was adhesive to

both tooth enamel and to stainless steel one would immediately

think of attaching orthodontic devices directly to the tooth
-9-

without the customary banding. Two authors in a series

of investigations

J ‘

1

' have explored this technic. In

the first article circular stainless steel orthodontic

buttons were cemented to polished enamel surfaces using

polycarboxylate cement, silico-phosphate cement, zinc

phosphate cement and copper phosphate cement and subjected

to tension after storage for 48 hours in water at 37°C. The

tensile strength bond values were 74 kgf/cm (1050 psi ;/

27 kgf/cm2 (380 psi), 4.6 kgf/cm2 (65 psi) and 23 kgf/cm

(330 psi), respectively. Further investigation showed

that the tensile bond strength of several experimental

polyacrylate cements were several times the magnitude of

those of other dental cementing media. Most of the failures

of the zinc polyacrylate cements occurred within me .....

and not at the cement-enamel interface.

After investigating the reaction of the bond lo

shear stress, to peel strength tests, to static and dynamic

fatigue tests, to thermal cycling, to surface roughness

variation and to contaminations likely to occur in the

mouth, the authors believed that limited

clinical trials are warranted in which the orthodontic

appliance parts are attached directly to the surfaces of

the teeth.
- 10-

Smith/ the inventor of the zinc polyacrylate cements,

is continuing his experimentation (at the University of

Toronto) v J by mixing other oxides with zinc oxide, with

and without sintering, and by using liquids containing polyacrylic acid of molecular weights from 5000 to 300,000.

Some of the combinations with powder-liquid ratios from

1.5 to 2.5 gave compressive strength from 631 to 914 kgf/crn3

(9,000-13,000 psi) and tensile strengths from 56 to 106

kgf/cms (800-1,500 psi). The solubility in water was less

than 0.03%. This low water solubility value may have been

derived by using the test for solubility and disintegration

in A.D.A. Specification No. 8 for Dental Zinc Phosphate

(9) Cement. The solubility in water using other test methods

( 24) is apparently much higher (Table 4). In fact, the high

water sorption, which caused dramatic decreases in strength

(24) and stiffness and increases in dimensions, is a very

important factor when considering the use of polyacrylate

cements in the mouth. The compressive strength is also

rate and temperature dependent which may in part account

for some discrepancies in values of physical properties

reported, by various investigators. Therefore, it is not

possible to compare directly the data given in Table 4 and

elsewhere in the literature.
There are not at this time sufficient laboratory data

and extended clinical experience to warrant the wholesale

substitutions of zinc polyacrylate cements for zinc phosphate cements in dentistry, but certainly limited clinical

use is and should be in progress primarily because of the

adhesion between zinc polyacrylate cement and enamel

.

( 23 ) How the adhesion occurs is not known. Smith

believes that polyacrylic acid reacts with calcium on the

surface of the enamel and that polyacrylic acid may form

complexes with proteins . No evidence is presented to

show that a chelation does occur.

The zinc polyacrylate cements are an exciting

development and the development of other carboxylate

cements is in progress.

Silicate Cement . Silicate cements have been used in

dentistry for about a century primarily as a restorative

material for use where esthetics and caries prevention

are of utmost importance.

When a pulverized complex alumino-silicate glass

containing magnesium, fluorine, calcium, sodium and
- 12-

phosphorous is mixed with an aqueous solution of orthophosphoric acid buffered by aluminum or zinc salts or

both, a hard strong mass results that simulates the

color and optical properties of the tooth.

The chief fault of these cements as a restorative

material is their solubility in the mouth. The average

life of a silicate cement restoration is about 3 to 4

years. Silicate cement restorations disintegrate in a

decay-like manner. That part of a silicate cement

restoration which is in a relatively self-cleansing

area will remain virtually undissolved while that part

which lies in an area where food and other debris

collect will be selectively dissolved. Even then,

there will be comparatively little recurrent decay about

silicate cement restorations probably because of their

high fluoride content and because this fluoride content

decreases the solubility of the enamel in acids.

Specification requirements, composition and values

of pertinent physical properties of some silicate

cements as obtained according to A.D.A. specification

procedures are given in Table 5. One sees that improvements have been made in these cements over the last few
Dental

Silicate

Cements:

Composition

and

Properties

kgf/cm 2=

14.223

psi

-13-

decades as reflected by decrease in the maximum

solubility values permitted in the American Dental

Association specification from 2.0% (1938-1950), to

1.4% (1950-1962) to 1.0% (1962- ), and an increase

in the minimum values permitted for compression strength

from 1260 kgf/cm2 (18,000 psi) (1938-1950) to 1620 kgf/

cm

2 (23,000 psi) (1950-1962) to 1700 kgf/cm2 (24,200

psi) (current). The testing time was decreased from

one week to 24 hours in the 1950 revision. This caused

the 24 hour values for solubility to decrease on the

average 0.25% from the one week values and the value for

compressive strength was on the average 100 kgf/cm2

(1420 psi) less at 24 hours than at one week.

The values obtained on retesting the silicate cements

on the List of Certified Dental Materials (as established

( 12 ) by the American Dental Association) in 1958 and in

(31) 1965, v also given in Table 5, reflect the decrease

in solubility and increase in strength of those silicate

cements between 1958 and 1965.

( 32 ) ( 22 ) Pulver took the analysis'* ' of a commercial

silicate cement powder and liquid (given at the bottom
- 14-

of Table 5) and calculated the approximate formula :--

Batch Composition of Cement Powder. --per cent by weight

as Si02 -39 . 9 ; Al 2 03 -30.2; CaF2 -4.0; Na3 AlF6 -19.2 and

Ca (XI2 P04 ) 2 *H2 0~6 . 7 . The liquid composition was by

weight per cent H3 P04 -41 .3 ; Zna (P04 ) 2 -17.8 and H2 0-4 0.9.

Pulver

^2 ) conci u ded that an aqueous solution of citric

acid would be a more appropriate test medium for

solubility than distilled water.

Wilson and his associates explored in exhaustive

(33-44) and scholarly investigations 1 ' the nature of

silicate cements with special emphasis on modifying

them so that they would endure the rigors of the mouth

environment better than the available ones. He interpreted from his results that there is not much probability

of significantly improving silicate cement. There are

just too many circumscribing parameters that relate to

the specific use of silicate cement in dental health

service.

Zinc silico- phosphate cements . The zinc sili co-phosphate

cements # as the name implies , are a hind of hybrid

between zinc phosphate cements and silicate cements,, but
-15-

their properties are closer to the silicate cements.

The zinc silico-phosphate cements arc probably the most

durable in the mouth of any of the dental cements based

on phosphoric acid and since they contain large quantities of fluoride, they are also probably anticar iogenic

Some of the cements are made by incorporating large

quantities of zinc oxide in the silicate cement glass

and at least one has a powder that is a mechanical

mixture of silicate and zinc phosphate cement powders

( 22 ) in an approximate ratio of 9 to 1 . Compositions ' of

each type, respectively, by weight per cent, follow:

Powder: Si02 - 14.6; Al 2 03 -15.6; Ca-3.2; F-5.9;

Na-2.9; P2 05 -2.1 ; ZnO-53 .2 ; MgO-2.3; H2 0-0.1 and

ignition loss at 120°C-0.1.

Liquid: PO^-55.7; Al-2.4; Zn-3.1 and Xg- 0.7.

Powder: Si02 -36 . 5 ; Al 2 03 - 26.3; Ca-5.9; F-12.0;

Na-4.6; Ps 06 ~3.2; ZnQ-9.4; MgO-0.5; and ignition loss

at 9 0 0 ° C- 6 . 9

Liquid: P04 -48.1; Al-1.9 and Zn-4.4.

The requirements of A. D. A. Specification No. 21

(45) for Dental Zinc Silico-phosphate Cement and the test

(31

)

values' for current American and foreign cements are

given in Table 6.

Properties

of

-Dental

Zinc

SilicoPhosphate

Cements

U -P 0 0 0

•P

G CM CM CM CMUuO

n <d

X cN o o o o 0 0 0

0) -P (T, • o o o o p P P

COG 2C -p o o o o -p -P 4- P 0 • rr, V o o o o O o 0

CO

X o o

>,

A 0 03 03 T3 T5 TJ

p

D £ • 0 0 0

ft 0 o o •P •P •P 0 ,C o 1 I i—

i—

rfD 1 1 a, a, ft

O, -3- E E E O r\i • o in in 0 0 0 C u ro m u u u H • • s o o

T3

G

C 0 CO

03 -P

p

-P 3 o ip >1 fO 0 • • • • •P P ,G X o o o O

•h tr> 0 • LO o in o H « -P • • • +1 +1 +1 +1 • H -P CM 5 —

1—

rP 1—

n c CM ID 03 in 3 -P 4-> • • • • <

1 CO 03 i—1 O o o O -H W Q

COCO e <u • CM CM «P C X

•h a; 03 o 1 o 1 +1 1 +1 i ft u £ in 1 in 1 1 i •H COro H 0 -P * * * * > ro * O o o O

•H * 0J ro r- CD CM « r: tn O p: o o o o ro CM CM CM 0 -P p C b o o o o

0) tn 3 •P \ r- r- PI +1 +1 +1 M C 0 £ 4-1 •—

i

i i—

i—

ft e a:O

OO o o £ ci a; iD r- CO CO O -P ^ i—1 CM in U m eg i—1 i

i i—1 •—

O'c • X

-P 0 03 CD 03 CO

ft

u £ 0

0) ° 0 ID ro i—1 i—i c/3 r- -P ro 3 +1 +1 +1 +i c O -P •p CM r- o in

03 £ i—

1—

0 • E c

*H •p in ro in ro H £ P

44 0 O Cl 'Tj 0 £ 44 >t -p 0 0 u~) CM i—

U 0 ft O —

1—

ro

C E —

i—l 1 0 • • • 0 0^ ft E O O o O

ft ft A^ +i +1 o mow ^0+1 +1 +1 +1 •P ' -P LO in 0 • *p W Q CM CM £O0O in CM in C X ro o1 • • • O P p M C ft ft i—

i—

U 6 O U -H ft O "co G 03 -P 0 0 P O a a o -P -P 0 -P C pp •P 0 c c H —1 G

ft

C

H -PH 0 ft E H -P 0 H 0 0

>1

H 0 1—1 i—

H 3 ft

C <U ft ft E H 3 E

Eh E i—

H

u 0 U rP 0 q qj 0 •P E •P O u U ft 0 CM ft O —

in 0 0 -p ro 0 G

4-4 -p -P c

*—

-P 0 0 -p g 0 G u 0 0 £ 0 •p 0 u Q 1 0 P u

4J •p o u 0 CL) G 4-4 P u 44 U e 0 •P 0 •p 0 O < £ o 44 rp -P -P 0 <D •P 0 >1 G CD 1 1 p ft i—

CO rC 0 0 rG 0 * '1 W CM Qg > P ft P 0 u 0 P P G

O’ c • G 0 0 0 >1 0 0 Q 0 •p rC CO u 12 Q

PC

C 53 IS) PU co

•H

4J0

•Huo

CO 0

o»G0

pc* **

kgf/cm s=

14.223

psi.
- 16-

Resin Cements . Composite cements with a plastic binder

such as poly (methyl methacrylate) and inorganic fillers

such as calcium or barium carbonate, quartz, mica,

alumina or calcium tungstate were used to a small extent

for almost 20 years. The mineral filler contents ranged

from 5 to 67 weight per cent. Because of their relative insolubility, it was believed that the resin cements

would displace zinc phosphate cements as a luting medium.

However, this has not occurred principally because:

(1) they possess a short working interval between completion of the mixing and seating of the appliance. A

crust forms on the mix quickly as the monomer evaporates;

(2) it is difficult to remove set cement that accumulates

in the spaces between the teeth when an appliance is

being seated; (3) water seeps at the resin cement- tooth

interface; and (4) they cause a more severe reaction on

the pulp than that caused by zinc phosphate cements.

When prepared at a standard consistency the resin

cements had setting times from 4 to 12 minutes, polymerization shrinkage from about 3 to S per cent by

volume, expansion (caused by water absorption) from
-17-

about 0.6 to 1.8 per cent by volume, aqueous solubility

from 0.1 to 0.4 per cent weight loss, optical opacities

from 0.45 to 1.00 C0>70 values, film thickness from 10

to 120 jam, a radiopacity of 0.8 to 2.9 film density on

a 2 mm thick specimen, and compressive strength from

527 to 879 kgf/cm2 (7,500 - 12,500 psi)

(46)

The resin composite cements are adhesive to tooth

enamel if the tooth is kept dry. Otherwise, water

penetrates along the resin cement-enamel interface and

rapid separation of the cement from the enamel occurs. '‘t0i

Direct Filling Resins, Composite and Adhesive Materials .

During World War II in Germany the auto- or selfpolymerization of dental acrylic resins was induced by

adding a tertiary amine (0.5 to 3 %) to methyl methacrylate

and 0.5% benzoyl peroxide to the powdered poly (methyl

(47

)

methacrylate) with which it was mixed. Soon there

appeared on the world dental market similar direct filling

resins and many thought there was here at last a replacement for the decades-old silicate cement. But this idea

was short lived because the direct resin restorations

discolored, leaked, caused severe pulp response, and
-18

allowed a high incidence of recurrent decay. For these

reasons they were abandoned by a great many practitioners.

Improvement made by the substitution of N, N-dirnethyl-ptoluidine for the previously-used tertiary amines gave

less discolored reaction products and the use of p-toluene

sulfinic acid as an initiator to decompose the organic

peroxide gave even better results. Later, ultraviolet

absorbers were added to the formulations so that most

present-day direct filling resins and composites have

reasonably good color stability in the mouth.

After these relatively simple self-curing direct

resin filling materials came the modern composites which

are partially displacing silicate cement. The composites

are based upon a three component system as illustrated

in Table 7 but adhesive cavity primers are largely in

the research and testing state.

The addition of the reinforcing fillers with an

appropriate coupling agent to bond the inorganic filler

to the polymer matrix improved the direct filling resins.

The volumetric shrinkage on polymerization was halved,

the compressive strength was doubled, and the modulus

of elasticity was increased about six fold (Table 8)
Table 7

Modern composite restorative materials

Component Contents*

Monomers

Liquid Stabilizers

Accelerator

UV absorber

Inorganic filler, treated with

Powder a silane coupling agent

Benzoyl peroxide

Coupling agent for improving the

Cavity bond between filling material

primer and hard tooth tissue

* These basic ingredients are supplied commercially

in various forms, such as paste-liquid, pastepaste or powder-liquid, formulated as two or more

components that are mixed prior to use.
Properties

of

composite

dental

restorative

materials

as

compared

with

direct

filling

resins,

human

enamel

and

dentin

•H

If) Qa

ro

CM

CM

Xm-jtr»

*
-19-

In addition / the coefficient of thermal expansion was

to from 40 to 18 x lCT c /°C

reduced from about 120 x 10” 6 /°C,/ [30-40 °C (86-104°F)

]

while that of the tooth crown (enamel and dentin)' is

about 10 or 11 x 10” 6 /°C. Other properties of the hard

tooth tissues are also presented in Table 8.

To the best of the author 1 s knowledge all of

currently successful filling resins are acrylic resins

or are adducts of acrylic / principally methacrylates

,

with other resins. The reason for this is that the

acrylic resins, principally methacrylates, most nearly

meet the circumscribing dental requirements as listed

in Table 9. It is not feasible to indicate these

requirements in the order of their importance. For

example, a resin may be perfect in all respects except

that it is black—and therefore, totally unacceptable

for restoring a front tooth in which esthetic requirements are paramount.

Many resins have been developed and tested but have

not reached commercial production. Among these are:

(1) Polystyrene which was injected into tooth cavities.

(55) The restorations failed because of poor marginal integrity.

Table 9

Dental Requirements of Plastic Filling Materials

1. Polymerizable in the mouth environment.

1.1 Suitable mixing, working and setting times.

1.2 Ease of placing and finishing.

1.3 Minimal residual monomer.

2. Optical characteristics that permit a formulation

that simulates the tooth.

2.1 Color match with the tooth.

2.2 Opacity similar to that of the tooth.

2.3 Matching index of refraction.

2.4 Resistance to staining in the mouth by foods, tobacco smoke, cosmetics and bacterial products.

2.5 Color stability in the mouth.

3. Biocompatibility and preventive capacity.

3.1 Not seriously irritating to the pulp and to the gingiva.

3.2 Low systemic toxicity.

3.3 General passivity.

3.4 Anticariogenic properties.

4. Dimensional stability.

4.1 Low polymerization shrinkage.

4.2 Low dimensional change on absorbing water.

4.3 A coefficient of thermal expansion as close

to that of the tooth as possible (10 x 1U” 6 /°C)

4.4 Minimum change on release of stress on absorption

of water.

5. Adequate mechanical properties.

5.1 Strength.

5.2 Elastic modulus.

5.3 Elastic limit.

5.4 Indentation resistance and recovery.

6. Adequate physical properties.

6.1 Abrasion resistance to food, dentifrices and teeth.

6.2 Softening point higher than temperatures encountered in the mouth.

7. Adhesive to tooth tissues.

8. Insolubility.

9. Low water absorption

10. Adequate shelf life.

11. Radiopacity.
- 20-

(2) Polyamide, which was also injected into tooth

cavities but was discontinued because the restorations

(55) failed cosmetically. (3) An aziridino polyester

composite that was introduced commercially in 1959

under the trade name of "Cadurit" had relatively poor

( 56 ) physical properties . '

' After a three year clinical

(57 58 ) trial it showed poor color stability and surface loss.

This material had inferior physical properties compared

to those of poly (methyl methacrylate) as determined in

the laboratory and had inferior clinical behavior—

reasonably good correlation. Cadurit is an example of

a filling material being placed upon the market seemingly

without adequate laboratory or clinical testing. (4) a

/ polycarbonate that was softened and injected into tooth

cavities. It maintained reasonable marginal accuracy

and was color stable. The material never reached

commercial production although one large company in

Germany made an injection apparatus for its use. The

material would be, in the author’s opinion, unable to

compete commercially with current dental restorative
- 21 -

matcrials because of the technic involved, (5) Epoxy

resins were thought to have possibilities as a direct

filling resin. At least one company attempted to

fabricate an epoxy material but it could not be used

clinically because moisture interfered with its polymerization and the dentin surface could never be made

( 59 ) moisture-free . (6) Cyanoacrylates , none of which

have proved successful as a direct filling resin but a

n-butyl-a-cyanoacrylate composite has some possibilities

as a dental cementing medium. Another cyanoacrylate,

methyl-a-cyanoacrylate, as a component for a composite

used as a fissure sealant in caries prophylaxis had

limited success but has now been abandoned for a (62)

new sealant composite containing the reaction product

of bisphenol A and glycidyl methacrylate^^ and is polymerized by UV light. The technic is simple and in

one year of clinical testing only one fissure became

uncovered. All treated teeth were free from decay after

one year, but matched control teeth had caries in 42%

(62) of the pits and fissures
- 22 -

The outstanding development in the preparation of

a successful composite restorative material to date has

been the work of R. L. Bowen, a research associate from

the American Dental Association at the National Eureau

of Standards . In his material, the resin

matrix is the addition-reaction product of bisphenol A

and glycidyl methacrylate (BIS-GMA) . Viscosity of the

resultant product was lessened when methacrylate monomers,

stabilizer, and accelerator were added. These constituted

the liquid component. The powder consisted of vinyl

silane-coated fused silica and benzoyl peroxide. Another

/ r- »7 \ silane now seems more appropriate.' BIS-GMA, while

not completely color stable, is used in almost all of

the commercially available composite restorative materials

made in the U.S.A. The trade names of some of these and

/ 68 69 ) some physical property values from two recent reports ' '

are given in Table 10. The methods used in references

68 and 69 were not usually identical which may account

for some of the differences among the data.

One group of workers ( 69 ) also reported the water

sorption of the four materials listed in Table 10 as about
Physical

Properties

of

Some!

Commercial

Composite

Dental

Restorative

Materials eu\ E

rQ r-l • >iJ) o w enu

01 (/) ^ o c o' it} ro m T5 E a -h

in i—

- o

4-> >1

w c & c w ,c c o 03 O' -H E c S

•H> - 0

03 4J 4-> • ,C -H -H 03 OWC W H O C H +J & <D

05 0 CU •H Q 'D U C -

0>-

cos

03-^ .C * O 0* a cr> <u c ^ * 03 O u a

to o

CD

C

a o E >

inadvertently

reported

as

10 3

lb/in^

in

(68)

-23-

1.5% weight gain for Addent 35, 1 „ 0% for Addent 12,

0.75% for Adaptic. The Dakor specimens during the

sorption test declined 3% in weight. The solubility

was about 3% for Dakor, about 1% for Addent 12, 0.5%

for Addent 35, 0.25% for Adaptic. The author is not

aware of any clinical investigations that might reflect

the foregoing laboratory findings or those reported in

Table 10. Comparisons are also difficult since there

is no American Dental Association specification for

the resin composite restorative materials, but standard

test methods have been adopted for specimen preparation,

indentation resistance and recovery, opacity and Knoop

indentation hardness. (70) other proposed tests are

being prepared for abrasion and abradability, adhesion,

dimensional change on hardening, on absorption of water

and on change in temperature, extractible plasticizer,

time of setting, sorption and solubility. All of

the foregoing are being woven into a future specification

of the American Dental Association for composite dental

restorative materials.
-24-

A new development involving three crystalline

(71

)

dimcthacrylate monomers with melting points slightly

above room temperature, which liquefy in ternary eutectic

proportions, seems suitable for composite formulations.

The three monomers synthesized by Bowen are: bis (2-methacryloxyethyl) isophthalate, (MEI) ; bis (2-methacryloxyethyl ) terephthalate, (MET) and bis (2-methacryloxyethyl )

phthalate (MEP) . They are condensation products of

2-hydroxyethvl methacrylate (HEMA) and the corresponding

(71) acid chlorides of the phthalic acid position isomers.

The approximate ternary eutectic proportions, 47% (ME I)

,

38% (MEP), and 15% (MET) melt at about 16°C. Since the

monomers are crystalline, they are relatively easy to

purify and since the ternary eutectic is a nonvolatile

liquid of a suitable viscosity at room temperatures and

has a very low toxicity, it was used in the formulation

of a resin composite which is now undergoing clinical

trials. The Epoxylite Corporation, P. 0. Eox 3397,

South El Monte, California 91733 has synthesized these

methacrylate monomers in custom batches.
- 25-

Reinforcing fillers, (bonded to the resin matrix

by a coupling agent) that have been advocated or used

in resin composite restorative materials include fused

silica, g; beta-eucryptile ^lSiO^), glass beads

and rods, "tricalcium phosphate" and certain porcelain

and ceramic materials. The latter, also called microcrystalline glasses, have attractive properties such as

high translucency, favorable refractive indexes and

thermal expansion coefficients approximating zero.

Adhesives . None of the dental restorative materials are

adhesive to untreated human enamel and dentin, which

they abut, with the possible exception of a methacrylate

resin in which an alkylboron compound, such as tri-n-

( 73 ) butylboron, is used as a hardening agent. An

experimental material of this type has been tested

clinically with evidence of adherence to the dentin, but

not in every case, so the usual retentive undercuts in

( 74 ) preparations for plastic restorations cannot be omitted.

In designing a restorative material that will adhere

to enamel and dentin under mouth conditions or in designing a cavity primer which would serve as a coupling agent
-26-

between enamel and dentin and restorative materials, it

is necessary to have extensive knowledge about calcified

tooth tissues. These tissues are really natural composites as they consist of associated organic and inorganic

portions in a structural entity with remarkable qualities.

The organic portion of dentin is about 20% by weight, almost all

of it being collagen, with fractional percentages of

carbohydrate and lipids. In enamel, the organic content

is less than 0.5 per cent. The major inorganic content

of enamel and dentin is hydroxyapatite. Other ions such

as sodium, potassium, chloride, fluoride, carbonate and

citrate are present but their exact relationship with

hydroxyapatite is not completely understood.

The cut surfaces of the cavity preparation are

moist and are covered by debris fiom the machining

involved. Various treatments have been used to prepare

this surface for the reception of an adhesive. Acids,

alkalis, enzymes and sequestrants have been used to

"clean" the cavity surface by removal of the loose or

partially attached debris as well as to remove selectively some of the organic or the inorganic portion of

the dentin and enamel . These pretreatments usually
- 27-

cnhance the adhesion as measured by mechanical tests

of various types. Adhesion test methods need to be

standardized so comparable values in the literature

will have some relevance to each other. The enhancement

of the adhesion by the pretreatment of the surfaces of

the tooth is probably in part not only due to removal

of the debris but also due to selective dissolving of

some of the components of enamel and dentin thus presenting a much greater surface area as well as a much

more reactive one. In addition, the removal of material

will not always be in parallel directions and thus there

will be undercuts available into which the low-surfacetension monomers can flow. Hence, on polymerization,

there will be considerable mechanical retention as well

(75

as retention from any chemical bonding that may occur.

A cavity primer, if it is a successful coupling

agent that bonds the hard tooth tissues to the restorative

material, must have chemical groups that will react with

the tooth surface and the hardening resin and that will

compete with the always-present water at the interface

between the cavity surface and the composite restorative
-28-

matcrial . The bond must bo strong enough to withstand

the stresses induced by polymerization, by subsequent

water absorption and by the differential in thermal

expansion of the tooth and the restorative material

The stresses induced by polymerization of direct filing

resins ranged from about 28 kgf/cm2 (400 psi) to 134 kgf/

cm2 (1900 psi) depending upon the geometry of the

cavity. ^ The values for stresses induced or relieved

by water absorption or by differential thermal expansion

of the interface materials have not been found in the

literature by the author.

There is a possibility that the stresses induced by

bonding at the interface may be undesirable. Consequently

a resilient type of acrylic or epoxide cavity primer has

, / —] -l \ been investigated. ' To the bes t of the author's knowledge,

( 11 ) cavity primers of these types v have not appeared on

the dental market.

Another development that has promise but has not

yet reached commercial development is an adduct of

IS) N- phenyl glycine and glycidyl methacrylate .

^ Tensile

bond strength values using this adduct between a dental
-29-

rcstorativo composite material and enamel, dentin and

fluorapatite (treated with a 10% aqueous solution of

the sodium salt of ethylencdiaminetetraaceticacid ) were

55 kgf/cm2 (780 psi), 26.7 kgf/cm2 (380 psi) and 41 kgf/

cm2 (580 psi), respectively. It is now under experimental

clinical trial.

Workers at the Gillette Research Institute first

(79) suggested' and have done considerable research on

(80) cavity primers based on polyurethanes. In these

(79,80) reports, several polyurethane-type compositions

were used to couple dentin to a variety of restorative

materials—amalgam, cement, direct filling resins and

composites. A typical adhesive was prepared from equal

parts by weight of tolylene diisoeynate (TDI) and a

polypropylene glycol. Sometimes 0.01 per cent of tripropylamine was used as a catalyst. Other isocyanates

and a number of polyglycols were used. Several adhered

well to dentin and to a variety of restorative materials,

were water resistant and performed well in thermal shock,

(79) tensile and compressive adhesion tests. Later,

reinforcing fillers such as titanium dioxide were used
-30-

to dilute the brown color of the polyurethanes as well

as to increase the adhesive strength, as did etching

with 50 per cent solutions of formic or citric acids.

The preferred polyurethanes were compounded principally

from refined castor oil and polymethylene polyphenyl

isocyanate (PAPI) which, with the Ti02 filler and etching

and debridement treatments of bovine enamel surfaces,

gave butt joint strengths of about 91 kgf/cm2 (1300

Other work, carried out by the Epoxylite Corporation,

gave a preferred formulation of a cavity primer entitled

NIH-302S-1 and consisting of:

• \ (80) psi) . v '

Part A Parts by weight

MDI (diphenylmethane-4,

4 '“diisocyanate) 100

Part B

Polybutadiene diol 5.0

Dibutyl tin laurate 0.575

Chloroform 94.425

Equal parts of A and B were mixed and applied to

bovine enamel (pretreated by etching for five minutes
-31-

with a 50% solution of citric acid) with a cotton

applicator and allowed to dry for five minutes. A

tensile bond strength of about 92 kgf/cm2 (1500 psi)

was obtained on specimens of bovine enamel-; 'mcrcomposite restorative material , the latter containing

82 per cent of inert f iller .

J

There has been some in vitro testing of polyurethanes

as cavity primers. A polyurethane varnish was used as a

cavity primer for 40 amalgum restorations which were then

submerged in a fluorescent dye solution and cycled

(82

)

0-37°-70°C. The microleakage was minimal. Other

formulations , using reacted products of various isocyanates

and prepolymers with isocyanate end groups and with an

excess of 2-hydroxyethyl methacrylate or the addition

product of bisphenol A and glycidyl methacrylate, did

not bond to tooth structure after one week in water and

softened and darkened during storage in water. ;

Inorganic polymers . Other than glasses and glass-like

ceramics, no inorganic polymers seem to have dental application as restorative materials as revealed by an extensive

(84) and excellent review.
32 -

Radiopaqueness . All materials used as operative or

prosthetic restorative materials should be radiopaque

so that they may be located radiographically if

accidentally ingested or aspirated. To achieve radiopacity without destroying the life-like appearance of

restorative materials was not accomplished until clear,

colorless glasses were developed with an index of

refraction near that of the suitable available synthetic

resins and having elements with relatively high atomic

numbers to give the desired radiopaci'ty „ At the same

time it was necessary that these glasses be suitable as

reinforcing fillers for dental restorative composite

materials . These glasses were prepared by melting

together compounds yielding silica, boric oxide, alumina,

barium oxide and barium fluoride. Barium made the

v glasses radiopaque, fluoride lowered the refractive

( 85 ) indexes and alumina tended to stabilize the glasses.

Biocompatibility . Dental restorative materials are

usually placed against crown dentin, the calcified tissue

between the thin enamel cover of the crown of the tooth

and the pulp chamber in the center, which is normally
- 33 -

filled with soft tissues, blood and lymph vessels and

nerves. The dentin is not solid but is filled with

small canals containing extensions of dentin forming

cells (odontoblasts) which line the pulp chamber. When

the dentin is cut in cavity preparation these fibrils

are also cut and some injury occurs to the odontoblasts.

If an irritant or toxic substance is placed against the

dentin, further injury or even death of the odontoblasts

may take place. Therefore, the restorative material

which is placed against the dentin should not irritate

the pulp unduly. Most materials cause some injury but

this injury is usually resolved and the odontoblasts

recover and lay down additional dentin as they retreat.

This dentin, sometimes called secondary dentin, is considered by some investigators but not by others as an

effective barrier against further injury.

The transient and prolonged effects of most of the

dental restorative materials in this review have been

reported by a host of investigators using rat, dog,

monkey and human teeth. Similar effects were observed

on all of the foregoing. A rough rating of severity from
-34-

the least to the most severe gives the following appro-

, x (36,37) ximate order: (1) zinc oxide-eugenoi based cements;

(23) (88)

(2) zinc polyacrylate cements; ^

' (3) zinc phosphate

cement

(89)

(4) zinc silico-phosphate cement; (5) res-

(90) (91) torative composites; (6) silicate cements; (7)

( 92 ) ( 93 ) direct filling resins; ' resin cements; .

' and (8)

( 94) black copper cements, ^ The earlier references have

been given. Much confirmatory work has since been done

and most of the work confirms that zinc oxide-eugcnol

cement is the blandest with almost no irritation and

that black copper cements produce the most severe reaction,

The foregoing order of arrangement is very relative and

should not be taken too literally but in all of the

materials cited except zinc oxide-eugenoi based cements,

and perhaps the zinc polyacrylate cements, an intermediary

I lining should be present between the restorative material

(95) and the dentin to protect the pulp.

Bioevaluation . As new materials are being developed so

rapidly, it is imperative that adequate bioassays be made.

In the case of dental restorative . materials this bioevaluation procedure has not been completely worked out
-35-

but the following have been suggested: (1) an

acute systemic toxicity test of the type known as LD^ 0

in which the dose. of the material ingested, in grams

per kilogram of body weight of the rat, will cause a

50 per cent mortality in 14 days; (2) a mucous membrane

irritation test on non-rodent animals in which the

material in question is held for 2 weeks in contact with

the mucous membrane. The degree of irritation is judged

by gross appearance as observed visually and by color

photographs and by biopsy of tissues in and out of contact

with the material; (3) a test for pulp irritation in which

at least 30 teeth from middle aged patients are restored

with the material and 30 similar untreated control teeth

are available. Serial extraction of the teeth

are made at 24 hours, 10 to 30 days and after 60 days,

respectively. After preparation for histologic examination,

serial sections are examined using twelve criteria and the

restored and controlled teeth compared. Also, guide lines

are being set up for the clinical comparison of restorative

materials
- 36-

Mouth conditions . The mouth is a rigorous environment

so only relatively passive materials such as noble metal

alloys , chromium-based alloys, porcelain and organic

polymers can resist the attack of foods and microbial

metabolic products.

Recurrent decay and anticariogenic properties : Recurrent

decay at the tooth- filling margin or at the cavity surfacefilling interface frequently occurs and especially in

persons with poor dental hygiene. Therefore, an ideal

restorative material should have anticariogenic properties

„

Silicate cement is almost unique among the dental restorative materials in this respect because there is almost no

recurrent decay around silicate cement restorations. One

study showed that the direct filling resins had about

10 per cent recurrent caries after three years and no decay

occurred around silicate cement restorations used as

( 97 ) controls. It is believed that the anticariogenic properties of silicate cement stem from its release of fluoride

( 30 ) to the enamel which decreases the enamel solubility.

Allergy . Allergic responses have been cited for all of

the restorative materials employed in dentistry but the
-37-

number of responses is only a very small part of one

per cent. This will hold true for countless substance;

with which humans come in contact.

Source references

Extensive information is presented for zinc

(4) (S3) oxrde-eugenol cements, EEA cements, zinc phosphate

cements, copper phosphate cement, zinc poly-

. . . (23-29) ...

'

, (22,33-44) acrylate cements, silicate cement, 7 ' zinc

, , . . (22,31,45) . „ (46) silico-phosphate cements, ' ' resin cements,

(57,62,67,68) composite restorative materials, dental ^ . (62,78,80) . . n (84) adhesives, inorganic polymers, and pulp

(95) reactions to restorative materials. In addition,

the following general sources are recommended: 99-112.

i
-38-

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