NATIONAL BUREAU OF STANDARDS REPORT

10 065

Progress Report

on CHARACTERIZATION OF A COMPOSITE RESIN-SILICA

MATERIAL DEVELOPED FOR TEMPORARY POSTERIOR RESTORATIONS

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
NATIONAL BUREAU OF STANDARDS

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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

31 1.05- 1 1-31 10560 June 30, 1969 10 065

Progress Report

on CHARACTERIZATION OF A COMPOSITE RESIN-SILICA

MATERIAL DEVELOPED FOR TEMPORARY POSTERIOR RESTORATIONS

by

Claire L. Burns,* John A. Barton, J r.+ and H. H. Chandler++

* Chemist, Dental Research Section, National Bureau of

Standards, Washington, D. C. 20234.

Guest Worker, Dental Research Section, National Bureau + of Standards, LTC from the U. S. Air Force.

++ Guest Worker from the American Dental Association in the

Dental Research Section, National Bureau of Standards, on leave from the Ohio State University.

This investigation is part of the dental research program conducted

by the National Bureau of Standards, and is supported by the Dental

Research Division of the U. S. Army Medical Research and

Development Command.

IMPORTANT NOTICE NATIONAL BUREAU OF ! for use within the Governmenj

and review. For this reason, whole or in part, is not autl Bureau of Standards, Washin

the Report has been specitica

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

ress accounting documents intended

is subjected to additional evaluation

re listing of this Report, either in the Office of the Director, National

, by the Government agency for which

I copies for its own use. <NBS>

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

CHARACTERIZATION OF A COMPOSITE

RESIN-SILICA MATERIAL DEVELOPED FOR TEMPORARY

POSTERIOR RESTORATIONS

Claire L. Burns, John A. Barton, Jr. and H. H. Chandler

Abstract

The objective of this investigation was to characterize

a resin-silica composite cement developed for use as a temporary

posterior restorative material. The material is based on a

monomer formulation of a ternary eutectic of isomeric phthalate

esters of 2-hydroxyethyl methacrylate, and a reinforcing filler

of vitreous silica and an X-ray opaque glass. The following

properties were evaluated: setting time, temperature rise on

setting, setting shrinkage, tensile and compressive strength,

elastic moduli (Young's and shear), thermal expansion,

indentation resistance, hardness, water sorption, solubility,

color stability and optical opacity.

1. Introduction

A resin silica composite cement, developed for use as a

temporary posterior restorative material was evaluated with

respect to its mechanical and physical properties. The material

is based on formulations previously developed at the National

1,2

Bureau of Standards for use in anterior restorations.

The monomer is essentially a liquid ternary eutectic of

3 isomeric phthalate esters of 2-hydroxy ethyl methacrylate.

The reinforcing filler consists of irregular particles of

vitreous silica and an x-ray opaque barium fluoride glass,

both of which were treated with a vinyl silane coupling

agent. ^ Benzoyl and lauroyl peroxides were added as accelerators.

The treated powder was sifted through a No. 100 United States

Standard sieve. It is desired that this material withstand

the forces of mastication and abrasion for at least two years;

be radio opaque so that it is possible to distinquish between

the material and remaining or recurring caries and that it

exhibit low pulpal irritation. Esthetic properties are of

secondary importance, since the material is intended for temporary

posterior restorations.

2. Experimental procedures

All test specimens were prepared at 23 ± 2°C and 50 ± 10%

relative humidity. Samples to be tested dry were stored
in a 37°C air bath, and those to be tested in the wet condition

were stored in distilled water at 37°C from the time of removal

from the mold until time of test. Three mixing consistencies,

1.10, 1.35 and 1.45 gm of powder, incorporated into 0.4 ml of

liquid, were used throughout this study. The 1.35 gm mix was

considered by the operators to have an optimum working consistency. Mixing was accomplished by incorporating the entire

amount of powder into the liquid at one time and spatulating for

one minute and 15 seconds on a glass mixing slab.

2.1 Setting time

Setting time was determined by the method outlined in

American Dental Association specification no. 9 for dental

. . 4 silicate cement with one modification. Instead of using a

single ring to contain the material, a Teflon mold, approximately

100 mm long x 50 mm wide x 6 mm thick, having six cylindrical

cavities approximately 6 mm in diameter, was used. This mold

was placed on a glass plate, filled from a single mix of

material, and each cylinder was covered with a small strip of foil.

2.2 Temperature rise on setting

Temperature rise on setting was determined by the method

5 described by Walcott and others using a mold which produced a

specimen of approximately 200 mm3

. The increase in

2
temperature above room temperature was measured, rather than

above 37°C, because the increase is small and occurs relatively quickly.

2.3 Setting shrinkage

Setting shrinkage values were obtained inter ferometrically

in much the same manner as described in American Dental Asso4 ciation specification No. 1 for alloy for dental amalgam.

A 5 x 10 mm mold, preheated to 37°C was filled with the

material and transferred to a 37 °C oven. Four minutes from

the beginning of mix the specimen was removed from the mold,

positioned on the dental interferometer and a fiducial reading was taken at five minutes. Additional readings were

made each minute during the first fifteen minutes, at varying

intervals thereafter, and a final reading was made at 24 hours.

2.4 Compressive strength

Six by twelve millimeter cylinders for compressive

strength determinations were prepared as described in

American Dental Association specification No. 9 for silicate

4 cement. These specimens were crushed using a head speed of

0.5 mm/min. Strength tests were made on specimens which had

been stored wet for 6 hours, 1, 7, and 28 days, and on

specimens which had been stored dry for 90 min, 1 day and

3
28 days. All time intervals were measured from beginning

of mix. Six specimens were prepared for each testing time.

2.5 Tensile strength

Specimen preparation size and time of test were identical

to that for compressive strength. Tensile values were

determined by the diametral compression method using a head

speed of 51. mm/min. In order to record the rapid change in

load, a Visicorder oscillograph was attached to the testing

machine

.

2.6 Elastic modulii

Young's modulus was determined by two different methods.

The first method employed Tuckerman optical strain gages,

with a one quarter inch gage length, attached to dumb bell

shaped specimenshaving a straight center portion approximately 2.5 x 2.5 x 20 mm. The specimen was tested using a

head speed of 0.13 mm/min. Strain gage readings were made

at 5 pound load intervals and the stress-strain curves

plotted. Six specimens of each consistency were tested.

6

An ultrasonic technique also was used to determine

both the Young's and shear modulus of the material. Cylinders,

10 mm in diameter by 6 mm long, were tested.

4
Additional shear modulus values were obtained using

7 the torsion pendulum method. Specimens, 2.5 mm in diameter and 20 mm long were tested.

All specimens used for moduli determinations were at

least one week old.

2.7 Coefficient of thermal expansion

The coefficient of thermal expansion for these materials

Q

was determined inter ferometrically. The values were

obtained from two heating and two cooling runs for specimens 4 mm in diameter x 8 mm in length tested wet.

2.8 Indentation resistance

The depth of penetration and recovery of the depth of

indentation were obtained by the method outlined in American

4 Dental specification No. 15 for acrylic resin teeth with

the exception of specimen size. In this study, the specimens were discs twenty mm in diameter and 2 mm thick.

Determinations were made on specimens stored in water for

1 1/2 and 6 hours, 1, 7 and 28 days, and on specimens stored

dry for 1 and 28 days. Three determinations on each of

three specimens (total of 9 determinations) were made at

all time intervals.

5
2.9

Hardness

Hardness values were obtained using the Rockwell

Superficial Hardness tester on the same type of specimen and at the same time intervals as for indentation

resistance. Five determinations on each of three specimens

(total of 15 readings) were made at all time intervals. The

Rockwell 30 W scale, thirty kilogram major load with a 3.2

mm diameter ball indenter, was used. The major load

remained in contact with the specimen for 15 seconds and

the dial reading was recorded 15 seconds after removal

of the major load.

2.10 Water sorption

Water sorption was determined by the method described

in American Dental Association specification No. 12 for

denture base polymers with the exception of specimen size.

In this study discs 20 mm in diameter by 2 mm thick were

used. In addition, after the 24 hours determination, the

specimens were replaced in distilled water and reweighed

at 24 hours intervals until constant .

2.11 Solubility

Solubility values were obtained by the method outlined

in American Dental Association specification No. 9 for

6
silicate cements. One set of specimens was removed from

distilled water after 24 hours immersion, and another set

was allowed to remain in distilled water for 7 days.

2.12 Color stability

Twenty by two millimeter discs of these materials were

exposed to the radiation of a lamp as described in American

Dental Association specification No. 12 for denture base

4 polymers for 24 hours and 7 days. Duplicate tests were

made for each ratio and time.

2.13 Optical opacity

The optical opacity of these materials were determined

by the method outlined in American Dental Association speci4 fication No. 9 for silicate cements.

2.14 X-ray opacity

Radiographs of teeth containing restorations made from

the composite material were made employing standard dental

procedures

.

3. Results

All values reported are averages and the coefficient of

variation was 10% or less in every case.

3.1 Setting time

A setting time of five minutes, as measured from beginning

to mix, was found for all three consistencies.

7
3.2

Temperature rise on setting

Results of temperature rise on setting are given in

Table 1. Temperature rise ranged from 5° to 7°C above

room temperature and occurred from four to 5 1/2 minutes

from beginning of mix.

3.3 Setting shrinkage

Typical curves for the setting shrinkage are given

in Figure 1. The initial change was very rapid and approximately 50/ of the shrinkage occurred within the first fifteen

minutes. The twenty-four hour value for the two higher

consistencies was 0.4% and that for the 1.10 gm mix was 0.5%.

3.4 Compressive strength

Compressive strength data, Table 2, for specimens

tested wet, show that the powder-liquid ratio did not

significantly affect this property. However, each consistency did show an increase in strength with time. Six

hour strengths were on the order of 165 MN/ms (24,000 psi)

and increased to about 196 MN/m2 (28„000 psi) after one

week. These data indicate strengths which are about 1/2

that of amalgam, comparable to silicates and twice that of

acrylic resins. Storing the specimens dry. Table 2, had

8
little or no effect on the compressive strength of these

materials at 24 hours, but dry specimens did tend to be

slightly stronger at 28 days.

3.5 Tensile strength

The early tensile strength of the thinnest mix, Table 3,

is lower than that of the other two consistencies, 26 MN/m2

(3700 psi) as compared to 30 MN/ms (4400 psi) . There is a

significant increase from the 6 hour to the 7 day and 28

day strength for all ratios. As in the case of compressive

strength, storage conditions did not have a significant effect

on the tensile strength values.

3.6 Elastic modulii

As can be seen from Table 4, there is little variation

in Young's modulus with the consistency of the mix. Variations in results by the two different methods is much

greater. The optical strain gage values presented in the

table were calculated up to stresses of 35 Myfn 2 (5,000 psi).

If only the data below 14 MN/m2 (2,000 psi) stress are used

the results of the two methods are much closer; approximately 14 x 10s MST/m3 (2.0 x 106 psi) for the strain gage

method as compared to 172 x 103 MN/m2 (2.6 x 10 6 psi) for

the ultrasonic technique.

9
Shear modulus is not significantly effected by the

stiffness of the mix, nor does the method used give great

variation. The torsion pendulum method value is approximately 6.5 x 10 3 MN/m2 (0.8 x 10 6 psi) as compared to 6.9 x

10s MN/m2 (1.10 x 10 6 psi) for the ultrasonic.

3.7 Coefficient of thermal expansion

Table 5 presents the values obtained for the coefficient

of thermal expansion. As can be seen, the value is dependent

upon the temperature range involved; all three consistencies

having smaller coefficients at the lower end of the temperature range. The 1.35 gm mix is consistently lower than

the other two consistencies, 30 ppm over the entire range

as compared to 39 ppm for the 1.10 and 34 ppm for the 1.45gn

mix. A possible explanation may be that the thinnest mix,

1.10 gm powder / 0.4 ml monomer contains less of the silica

filler. The 1.45 gm mix is quite stiff, which makes it

difficult to insure a homogeneous specimen. These coefficients

of thermal expansion are approximately 1/4 to 1/3 that of

the acrylics and about 10 ppm higher than amalgam.

3.8 Indentation resistance

The powder liquid ratio does not have a significant

effect on the indentation resistance of these materials.

Table 6.

10
They do exhibit a decrease in depth of penetration and an

increase in percent recovery on aging from 90 minutes to

28 days. Values for both properties of specimens stored

dry were within a few percent of the values for specimens

stored wet.

3.9 Hardness

There appears to be a slight difference in the hardness of the thin mix and the heavier ones at early times,

Table 7, but this difference decreases with time and

could not be considered significant after seven days. Specimens stored dry gave values within 2 hardness numbers of

the values obtained on the wet specimens. This is within

the reproducibility of the test method.

3.10 Water sorption

Water sorption, Table 8, after 24 hours is 0.2 to

0.3 mg/cm

2

. Continuing the soaking for seven days increased

the value to 0.4 mg/cm2 with no significant difference in

the values for the three consistencies.

3.11 Solubility

Solubility of this material is low when compared to

silicate cements. Table 9. The specification limit for

solubility of silicate cements is 1.0% after 24 hours.

11
Immersing the composite resin in distilled water for 24 hours

gave a solubility of 0.15%. After 7 days immersion, the 1.10

and 1.45 gm mixes increased to 0.22%, but the 1.35 gm mix

remained unchanged.

3.12 Color stability

Color stability of these materials is good. Even

after 7 days exposure to the lamp, there was no perceptible

color change.

3.13 Optical opacity

This material is somewhat more opaque than silicates.

All three consistencies were slightly higher, between 0.55

and 0.60, than the 0.55 Co7

0

contrast ratio albwed for

silicate cements

.

3.14 X-ray opacity

Figure 2 illustrates the x-ray opacity of these cements.

The restorations in the distal and mesial of the left central

are made fom a composite resin which did not contain a radio

opaque glass. Those in the mesial and distal of the right

central are made from the material under investigation.

4. Discussion

The data reported indicates that accurate proportioning

is not a critical factor for optimizing the properties

12
evaluated. The five minute setting time provides sufficient

working time for normal clinical use. Considering the size

of the specimen, approximately 200 mm

3

, a temperature rise of

5° to 7°C would not be considered sufficient to injure the

pulp. While the compressive strength of these materials

is similar to that of silicate cements, the tensile strength

is 5 to 10 times the reported values for silicates and

about 3/4 the value reported for amalgam. The water

sorption and solubility are low as compared to acrylics

and silicate cements respectively. Although these composites

are somewhat more opaque than silicates or natural tooth

structure, this is not a great disadvantage since the

material is intended for temporary posterior restorations.

A significant advantage of this material is its radioopacity, which permits dilineation of the cement and remaining

or recurring caries.

5. Conclusions

On the basis of the physical and mechanical properties

reported, it appears that this composite resin cement has

potential as a temporary posterior restorative material.

Since no criteria are available to determine from laboratory

data alone, whether or not a material will be successful

13
in use, clinical

now necessary to

for its intended

research and pulpal response

ascertain the suitability of

purpose

.

tests, are

the material

14

Table 1

Temperature Rise on Setting

P : L*

Temp . ** Rise

°C

Peak

Time

min

.

1.10 6.7 4.0

1.35 4.9 5. 5

1.45 5.1 5.5

* Gm. powder in a 4 ml monomer

** °C above room temperature

16
Table 2

Compressive Strength

' —^

P : L* 1 . 10 1 . 35 1 . 45

Aqe PSI MN/m2 PSI MN/ms PSI MN/ma

6 hr s. -wet** 24,500 169 24,400 168 23,600 163

24 hr s. -wet 26,600 183 26,200 181 25,700 177

dry*** 26,400 182 26,000 179 26,700 184

7 days-wet 28,600 197 28,500 196 29,200 201

28 days-wet 27,200 188 27,600 190 27,500 190

dry 28,500 196 31,200 215 29,200 201

*

**

***

Gm powder

Specimens

Specimens

in 0.4 ml

stored in

stored in

monomer

distilled water

37 °C air bath

at 37°C

17
Table 3

Tensile Strength

^7 — 1 . 10 1 . 35 1 . 45

Age PSI MN/m^ PSI MN/m2 PSI MN/ms hrs.-wet* 6 ** 3,700 26 4,400 30 4,400 30

24 hrs.-wet 4, 700 32 5,300 36 4,800 33

dry*** 4,800 33 4,600 32 5,200 36

7 days-wet 5,900 41 5,900 41 5,500 38

28 days-wet 5,200 36 5,700 39 6,000 41

dry 5,400 37 5 , 300 36 5,600 39

* Gm powder in 0.4 ml monomer

** Specimens stored in distilled water at 37°C

*** Specimens stored in 37°C air bath

18
Table 4

Elastic Moduli

* Gm powder in 0.4 ml monomer

19
Table 5

Thermal Expansion

P : L*

24-42 °C

PPM/°C

42-58 ° C

PPM/°C

24-58 ° C

PPM/°C

1.10 37 41 39

1.35 28 32 30

1.45 31 38 34

* Gm powder in 0.4 ml monomer

20
Table 6

Indentation Resistance

(Wet Storage)

P:L* 1.10 1.35 . 1.45

Age\^^ depth of

penetration

mm

Recovery

%

depth of

penetration

mm

Recovery

%

depth of

penetration

mm

Recovery

%

90 min. 0.08 54 0.07 56 0.07 58

6 hrs

.

.07 64 .07 63 .07 67

1 day .06 73 .07 69 .06 70

7 days .06 73 .06 74 .05 74

28 days .05 74 .06 77 .05 78

* Gm powder in 0.4 ml of monomer

21
Table 7

Hardness

P : L* 1.10 1.35 1.45

Aqe 30 W 30 W 30 W

90 min. 42 50 51

6 hr s

52 57 59

1 day 61 65 64

7 days 68 71 72

28 days 69 72 72

* Gm powder in 0.4 ml of monomer

22
Table 8

Water Sorption

P : L*

Aqe

1.10

mq/cm

2 1.35

mq/cm

2

24 hrs. 0.25 0.26

6 days 0.40 0.39

7 days 0.42 0.39

* Gm powder in 0.4 ml monomer

Table 9

Solubility

P : L*

Aqe

1.10

%

1.35

%

24 hrs. 0.16 0.15

7 days 0.22 0.15

* Gm powder in 0.4 ml monomer

m

1.45

g/cm2

0.16

0.33

0.35

1.45

_%

0.16

0.22

23

Fig. 2. Radiograph of Class III

restorations

.

A is made from a commercial product

B is made from the experimental material

.
References

1. Bowen, R. L. Properties of a silica reinforced polymer for

dental restorations. JADA 66:57.

2. Bowen, R. L. Dai tal filling material comprising vinyl silane

treated fused silica and a binder consisting of the reaction

products of bis phenol and glycidil acrylate, U. S. Patent

3,006,112, 1962.

3. Bowen, R. L. Crystalline Dimethacrylate monomers. Manuscript

in preparation.

4. Guide to Dental Materials, (Fourth Edition), American Dental

Association, 211 East Chicago Avenue, Chicago, Illinois 60611.

5. Walcott, R. B, Paffenbarger G. C. and Schoonover, I. C.

,

Direct resinous filling materials: temperature rise during

polymerization, JADA 42:253, March 1951.

6. Dickson, G, and Oglesby, P. L. , Elastic constants of dental

amalgam. J. Dent. Res., 46:1475 November-December , 1967.

7. Barton, J. A., Jr., Dickson, G., Kumpula, J. W. and Oglesby,

P. L., Determination of Shear Modulus of Dental Materials by

means of a Torsion Pendulum. Manuscript in preparation.
8 . Dickson, G. and Zelenka, D., Automatic Recording Thermal

Expansion Apparatus, Abstract IADR, 1962.


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