NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

3 1 1.05-1 1-31 1056 1 June 30, 1970 10 273

Progress Report

on PHYSICAL PROPERTIES OF A

RADIOPAQUE DENTURE BASE MATERIAL

H. H. Chandler,* R. L. Bowen+ and G. C. Paffen barger

+

* Research Associate, American Dental Association Research Program

in the Dental Research Section, National Bureau of Standards,

Washington, D. C. on a two-year leave of absence from The Ohio

State University College of Dentistry, Columbus, Ohio 43210.

+ Research Associates, American Dental Association Research Program

in the Dental Research Section, National Bureau of Standards,

Washington, D. C. 20234.

This investigation was supported in part by Research Grant DE02742-01

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 Dental Research Division of the U. S. Army 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 Admim stration.

NATIONAL BUREAU OF ST

for use within the Government, and review. For this reason, th whole or in part, is not authoi Bureau of Standards, Washingti

the Report has been specifically

IMPORTANT NOTICE

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

ss accounting documents intended

subjected to additional evaluation

listing of this Report, either in

e Office of the Director, National

jy the Government agency for which

:opies for its own use. <NBS>

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

PHYSICAL PROPERTIES OF A RADIOPAQUE

DENTURE BASE MATERIAL

ABSTRACT

Physical properties were determined for radiopaque composite

denture base materials consisting of poly (methyl methacrylate)

as the matrix and 30, 40, and 50% by weight of a silane-treated

barium fluoride-containing glass powder as the reinforcing

filler. Specimens without glass were included for comparison.

All of the materials met the requirements of American

Dental Association Specification No. 12 for Denture Base

Polymer except that the material containing 50% glass had

less deflection than the minimum required at the 5000 Gm

load in transverse testing.

There was little or no difference among the materials

with respect to hardness, indentation resistance, water

sorption, color stability, and resistance to drop impact.

Addition of glass to the 30% level decreased the transverse strength while 50% glass specimens had slightly greater

transverse strengths as compared to specimens with no glass.

In general, the addition of glass increased the time to reach

the packing stage, densities, and Young ' s, bulk, shear, and

flexural moduli, had only slight effect on solubility and
2

decreased the cold-cure repair ability and the coefficient of

linear thermal expansion.

The solubility of the glass powder was about four times

that of powdered porcelain teeth after 24 hours, and totaled

0.55% after five days.
3

PHYSICAL PROPERTIES OF A RADIOPAQUE

DENTURE BASE MATERIAL

Introduction

Evidence of need for radiopaque denture base materials

was presented in a previous report. 1 A review of 123 cases

of denture foreign bodies indicated that radiographic localization would be facilitated if the base material was radiopacue.

Another report described the characteristics of a series

of trial specimens made to determine what combinations of

polymers and radiopaque glass yielded specimens having optical

* translucency, radiopacity, and handling and molding properties

that would make them suitable for further research and development. 2 Although several combinations of polymers and glasses

had promise, the material selected for further investigation

was one composed essentially of poly (methyl methacrylate) (PMMA)

and a silane-treated radiopaque glass. Mixes containing these

materials could be compression molded using methods and equipment in common use and they could be pigmented and opacified to
4

yield specimens that had optical translucency and color that

simulated oral soft tissues. Also, radiographic diagnosis

was facilitated by the radiopacity gained in specimens containing from 29 to 57% of the glass filler.

In the present investigation, some pertinent physical

properties were determined on radiopaque, composite, denture

base materials containing 30, 40, and 50 weight percent glass

as the filler and PMMA as the matrix. The properties of the

same denture base material without glass were also determined

for comparison and control.

Properties investigated included: packing facility,

water sorption, solubility of the composites and of the

deflect ion

glass filler, color stability, transverse / and strength,

repairability , indentation and recovery, hardness, density,

resistance to impact fracture. Young's modulus, flexural

modulus, shear modulus, bulk modulus, and thermal expansion.

A subsequent paper 3 will describe the use of these materials in the construction of twenty technic dentures to
I

- 5 -

determine the dimensional changes occurring as a result of

processing and water storage, the effects of silane treatment

of porcelain teeth, and the mixing, molding, and finishing

characteristics during actual conditions of denture fabrication.

Materials*

The following materials were used in making the specimens :

1.) Liquid. The liquid was composed of methyl

methacrylate (MMA) (Rohm and Haas Co.) 98.5%

by weight and ethylene dimethacrylate (Borden,

Inc.) 1.5% by weight. The MMA contained 35

ppm of 2, 6-di-t.-buty 1-4-methyl phenol ( BHT ) as

a stabilizer. The liquid was prepared and

allowed to stand for 24 hours before use.

* Certain commercial materials and equipment are identified in

this paper to specify adequately the experimental procedure.

In no instance does such identification imply recommendation

or endorsement by the National Bureau of Standards or that the

material or equipment identified is necessarily the best

available for the purpose.

¥
6 2.

) Powder. The powder was a homopolymer of MMA

containing 5% by weight of dibutyl phthalate as a

plasticizer (Esschem Co., Division of Sartomer

Resins, Inc. Type #P 5-69-2Q3 ) . The polymer was

composed of beads with diameters from 5 to 120 pm

with most of the material consisting of beads

greater than 40 pm in diameter. The refractive

index was 1.493.

3.

) Filler. The radiopaque glass (Corning Glass

Works Code X816JL) had the following batch

formulations Si02 , 44; BaF a , 28; B 2 03 , 16;

and Al 3 03 , 12 in mole percent. 4 The formulation given in weight percent is; BaF s , 50;

SiOs , 27; A1 3 03 , 12; and B 2 Q3 , 11. The powder

was elutriated by mixing, settling, and decanting

in an attempt to remove very small particles and

then treated with 3-methacry loxypropy ltr imethoxysilane (Union Carbide A-174). Both the elutriation procedure and silane treatment were described
7

previously. 3 After silane treatment, the powder

was passed through a U. S. Standard Sieve No. 100

(maximum opening 149 pm) to remove any lumps of

caked or agglomerated material. The particle

sizes of the powder were about 1 to 50 pm and

the refractive index n^ ^ was 1.535. Some testing

D

was done using the glass powder as received (without silane treatment). The powder was tumbled

before use to ensure thorough mixing.

4.

) Pigment and opacifier. Most of the specimens were

pigmented with cadmium red (United Color and Pigment

Co.) and opacified with anhydrous titanium oxide

(Fisher Scientific Co.).

5.

) Repair material. NuWeld (The L. D. Caulk Co.,

Division of Dentsply International, Inc.).

This is a cold-curing powder-liquid system.

Methods

Testing was carried out on specimens containing 0, 30,

40, and 50% by weight of the radiopaque glass. In this

report, mixes and specimens will be referred to on the basis

of their glass content in weight
8

percent. A glass content of 30% yielded specimens having

the approximate minimum necessary radiopacity with good

working properties in the mix; a glass content of 50%

represented the approximate upper level of glass which could

be used and still maintain acceptable working properties; the

40% content represented a compromise between radiopacity and

working properties.

Table 1 lists the compositions of the various mixes with

the four different glass contents. To each mix was added

0.029% of cadmium red pigment and 0.029% of titanium oxide

opacifier. To gain uniform distribution of the pigment and

opacifier, they were first mixed thoroughly with a small

amount of the polymer. The remainder of the polymer and

the glass was then added with additional thorough mixing.

Attempts to mix all of the dry ingredients at one time resulted in a non-uniform color.

Unless e > -.wise specified, all specimens were cured

in flasks immersed in water at 73 ± 2°C for 1-1/2 hours and

then in boiling water for 1/2 hour. The flasks in the

¥
8a

Table 1 * Composition of mixes

Ingredients Composition of Mixes

wt % wt % wt % wt %

Liquid 20.4 23.0 21.0 20.0

Powder 79.6 47.0 39.0 30.0

Filler 00.0 30.0 40.0 50.0
F

I

!

F

F

F

F

F

F

F

F

i

i

F

F

F

F

F

F
9

clamps were then air cooled at 23 ± 5°C for 1/2 hour and

immersed in water at 23 ± 10°C for 15 minutes. In some

cases, the flasks were allowed to cool to room temperature

in the curing bath.

Packing, water sorption, water solubility, transverse

deflection and strength, and color stability: The tests

for packing, water sorption, water solubility, transverse

deflection, and color stability were run according to the

methods outlined in American Dental Association Specification

No. 12 for Denture Base Polymer 6 with the following exceptions

(1) number of specimens used, (2) the mold for the transverse

specimens was lined with an alginate separating medium instead of tinfoil, and (3) the mold for the sorption and

solubility specimens was lined with polyethylene trial pack

separating sheets as there was a tendency for the cured 40

and 50% glass specimens to stick to the stainless steel mold.

After the original 24-hour sorption and solubility tests

had been completed, the disc-shaped specimens were resurfaced

with #240 silicon carbide paper in order to remove the resinrich outer surface. Another 24-hour test was then completed

followed by a ten-day test during which the immersion water
10

was changed seven times. Four specimens for each material

were used.

Additional specimens for transverse deflection and strength

testing were made using 30 and 40% levels of the glass which

had not been silane treated. Four specimens of each were made.

Repairabil ity

Repairability of the materials containing

0, 30, and 40% glass were determined by transverse deflection

and strength tests using a method described previously. 6 A

6.4 mm section was removed from the middle of each of the plates

from which the transverse bend specimens were to be machined.

The two ends of the plates were then repositioned in the flask

and repair material was added and cured. Four transverse bend

specimens were then machined from each of the repaired plates

and tested according to the method outlined in American Dental

Association Specification No. 12. The following repairs were

made: 30% glass specimens were repaired with material containing

30% glass, heat cured and with NuWeld; 40% glass specimens were

repaired with material containing 40% glass, heat cured

and with NuWeld; 0% glass specimens were repaired with NuWeld.
11

Indentation and recovery: Specimens for indentation

and recovery and for hardness were made in upper denture

flasks in dental stone molds 2.8 x 27 x 29 mm lined with an

alginate mold lining material. Two specimens of each material were made and finished so that the top and bottom

were parallel. The test sides were hand finished with silicon

carbide paper ending with number 600.

Indentation and recovery testing was done with a Rockwell Superficial Hardness Tester. using the 30Y scale as

outlined in American Dental Association Specification No.

15 for Acrylic Resin Teeth. 7 Three tests were made on each

of the two specimens both dry and after 14 days storage in

water at 37°C.

Hardness; Hardness values were obtained using the

Rockwell Superficial Hardness Tester and the 15W scale. A

3.17 mm steel ball was applied at a minor load of 3 kg and

the dial gauge was set at zero. A major load of 15 kg was

then applied for 15 ± 1 second and the dial reading was recorded. Five tests were made on each specimen both dry and

after 14 days storage in water at 37°C.
12

DensityThe densities of the four different materials

were found by determining the weight and volume of specimens

that had been machined for ultrasonic modulus testing.

Drop impact resistance: Resistance to drop impact was

measured with an instrument similar to one described by

Cornell et al. 8 The test used in this investigation involved

the determination of the mean height at which specimens

fractured when subjected to a falling steel ball. The instrument used is seen in Figure 1. A close-up picture of

the specimen holder is seen in Figure 2

Specimens for the drop impact test were made in denture

flasks (3 specimens in each flask). The molds were disc

shaped, 3.4 mm deep and 38.1 mm in diameter with a slight

taper so that the specimens could be easily removed. After

deflasking, the flash was removed from the specimens with a

carborundum stone and surface blemishes were removed by hand

sanding. The hand sanding also served to flatten the specimens

so that they were stable when placed in the holder. The thickness of each specimen was measured and those that were significantly thicker than the others were further sanded to bring
13

them within the range of 3.25 to 3.45 mm. Each specimen was

placed in the holder (Fig. 2) to insure that it did not bind

and was adjusted so that there was slight lateral movement.

Thirty-six specimens of each material were made and stored

in water at 37°C for at least one week prior to testing.

Testing was done basically as described in ASTM designation D-2463-65T 9 for determining the drop impact

resistance of polyethylene containers. A specimen was placed

in the holder and a steel ball 20.64 mm in diameter and

weighing 35.77 Gm was dropped onto the middle of the specimen

from a height estimated to be just great enough to cause

failure. If failure occurred the ball was dropped on another

specimen from a height of 3 cm less than the initial drop

height. If failure did not occur on the initial drop, the

ball was dropped from a height 3 cm greater than the initial

drop height. All of the specimens were tested in this manner.

The height of each drop was either increased or decreased by

3 cm according to the results of the previous drop. No specimen was used more than once. Failure was considered to be

any crack or fracture visible to the naked eye.
14

The mean failure heights and standard deviations were

computed using either failures or non-failures according

to which was less frequent. 10 The results of the first 10

drops were used only to establish the approximate mean failure

height as a starting point for the succeeding drops and were

not used in the computations.

Thermal expansion; The coefficient of linear thermal

expansion of the materials was determined by the use of a

fused quartz tube apparatus. 11 The apparatus consisted of

a glass water jacket surrounding a quartz tube within which

was placed the specimen with a quartz plunger on its top.

Expansion was measured by means of a dial gauge in contact

with the top of the quartz plunger. Temperatures from 5

to 70° C were obtained by circulating water in the jacket

from a temperature controlled water bath.

For the thermal expansion measurement, two specimens

(203.0 x 11.1 x 11.1 mm) of each material were formed in a brass

molu- Ler packing, the mold was covered with brass platens

under pressure from "C" clamps. Curing was carried out at

73°C for nine hours after which
15

the mold was allowed to cool to room temperature in the

curing bath. This curing cycle was selected because of

the increased likelihood of porosity in specimens of this

size if curing cycles involving higher temperatures had

been used. Specimens were removed from the mold, the flash

removed, and the lengths measured. They were stored in

water at 23 ± 2°C for at least 7 days before testing. In

order to determine the effects of longer water conditioning,

one 30% glass-containing specimen was tested again after

23 days.

The testing was begun on each specimen by first raising

the temperature in the jacket to 70°C and retaining it at

that temperature until no movement of the dial gauge indicator was noted. The initial reading was recorded after

which the temperature was lowered about 10°C and again allowed

to remain until no movement in the gauge was observed. This

was repeated at each 10°C interval to 5°C (the last interval

being only 5°C) after which the temperature was raised in 10°C

intervals to 70°C. The entire cycle from 70°C to 5°C and back

to 70°C was repeated giving a total of 4 determinations for
16

each specimen and 8 for each material. The coefficients of

thermal expansion were determined for the ranges of 5 - 37°C

and 37 - 70°C, in order to compare the results with a previous

study

1

Resistance to deformation: The flexural modulus was

calculated using the data obtained in the transverse bend

tests. A tangent was drawn to the initial straight line

portion of the load deflection curves and the slope of

the tangent determined. The modulus was calculated from

the equation:

F = IlJB

B 4bd3

where E = modulus in bending; L = beam span; m = slope of the

B

tangent; b = beam width, and d = beam depth.

Young's, shear, and bulk moduli were determined by an

ultrasonic pulse-echo technic described elsewhere

1 ^ The

technic involves the determination of the transit-times of

ultrasonic pulses through specimens of the test materials.

Velocities for both transverse and longitudinal impulses were

obtained. These velocities and the densities were used in

the following equations to compute the various moduli for each

1 2 material
17

Young's modulus E

Shear modulus G = pvf

Bulk modulus K = p (3Vl - 4V^

)

3

Where p = density

V T = transverse wave velocity

VL = longitudinal wave velocity

i

-

r

Specimens for the ultrasonic test were made by turning

rods of each material on a jeweler's lathe to a uniform diameter

of 8 - 9 mm. The rods were sectioned to form four cylindrical

specimens with lengths of about 6, 12, 19, and 2 5 mm for each

material. The specimens were stored in air at 23 ± 2°C for 7 to

14 days before testing.

Young's modulus was also obtained by the use of a

dynamic modulus tester (H. M. Morgan Co., Inc. Model PPM-SR)

with a planar mount. It is similar in principle to the

ultrasonic method in that it measures the transit time of

a sonic pulse through the test material. Specimens for the

dynamic modulus tester were formed in dental stone molds in
18

denture flasks. Specimen size was 2.2 x 12 x 75 mm. They were

tested dry and after 21 days storage in water. Young's modulus

was calculated from the following equation:

E = pC3

where E = Young's modulus? p = density of the material,

and C = velocity of the impulse.

Glass solubility: The water solubility of the silane

* treated glass powder was determined each day for 5 days. The

1 day water solubilities of the glass powder as received and

of powdered porcelain denture teeth were also determined for

comparison. All tests were run in duplicate. The porcelain

teeth (Trubyte-Nue Hue, Dentsply International, Inc.) were

cleaned in boiling detergent solution, washed with chloroform

and rinsed with boiling water. They were crushed in a steel

mortar to reduce them to particle sizes of about 2 mm. The

particles were placed in a porcelain jar mill with Burundum

grinding cylinders (The United States Stoneware Co.) and

milled dry for 16 hours. The resulting powder was passed

through a U. S. Standard Sieve No. 100.
19

One part by weight of each test powder was added to 9

parts by weight of water and the mixtures were stirred for

24 hours with a suspended Teflon® stirrer. The mixtures

were then filtered through a Millipore filter (maximum

opening 0.22 pm, Millipore Filter Co.) and the filtrates

were placed in tared weighing bottles. The water was

evaporated and the bottles dried to constant weight in a

vacuum oven at 95°C and about 33.7 kN/m3 (250 mm Hg ) . A

stream of air was passed through the oven during the drying

procedure. Solubility was determined on a percent basis.

A spectrochemical analysis was made on the 24-hour

residue of each material.

Results and discussion

Mixing and packing: All four materials complied with

the packing test in American Dental Association Specification No. 12. Each material entered all of the 0.75 mm

holes in the brass die at least 0.5 mm and in most cases

1.0 mm or more. There was little difference among the
20

materials except that those mixes containing 40 and 50% glass

tended to adhere to the brass die. The addition of glass

did not reduce the consistency enough to cause difficulty in

completely filling a denture mold.

However, differences did exist among the mixes in that

it required more time to reach the packing stage as the

percentage of glass was increased. The approximate times

to reach the packing stage varied from 16 minutes for a mix

containing no glass to 22 minutes for a mix containing 50%

glass. This reflects an increasing ratio of monomer to

polymer

Water sorption and solubility: The results of' the tests

for water sorption and solubility are listed in Table 2. The

data for sorption indicate that the addition of glass had

little effect and the values for all glass levels fell well

within the requirement of American Dental Association Specification No. 12. There was an indication that the glassresin interface was not serving as a point of entry for water
20a f

Table 2 • Water sorption and solubility i

i

l

J eight

Glass

Sorption* Solubilityt [

24 hr

24 hr*

resurfaced

10 days

resurfaced 24 hr

24 hr*

resurfaced

, 10 days

resurfaced

1 % mg/cm

3 mg/cm

3 mg/cm2 mg/cm2 mg/cm2 / 2 mg/cm |

0 0.4 0.4 0.4 0.00 0.00 0.01 j

30 0.4 0.4 0.4 0.00 0.00

! 0.02

40 j 0.4 0.4 0.4 0.00 0.01

I 0.02

i

50 | 0.4 0.3 0.3 0.01 0.01 o • o u>

1 ADA

spec

1

0.7

max

.

— 0.04

max

.

* Average increase in weight per surface area of four discs 50 mm

in diameter and 0 . 5 mm thick after immersion in Ha 0 at 37° C for

the time specified.

t Average loss in weight per surface area of four discs, 50 mm in

diameter and 0.5 mm thick after immersion in Ha 0 at 37°C for the

time specified and dried to constant weight.

* Hand sanded on #240 silicon carbide paper to remove the resinrich surface.
I

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21

since the sorption values did not change appreciably after

the specimens were resurfaced even after 10 days water

immersion

.

The water solubility values also fell well within the

range allowed by American Dental Association Specification

No. 12. Resurfacing and longer storage in water caused

some increase in solubility, especially of the glass containing specimens. It appeared, therefore, that the slight

increased solubility was perhaps due to glass dissolution.

Color stability; All of the materials complied with

the color stability test in American Dental Association

Specification No. 12. There was still no perceptible

color change in the specimens after 72 hours under the sun

lamp

.

Transverse deflection and strength? The results of the

transverse bend tests are listed in Table 3. This test

simulated one type of stress introduced into a denture

base material during function. It can be seen that the

materials containing glass were much stiffer in transverse

bending than the material containing no glass and the
!
Table 3*

Transverse

deflection*

and

strength;

repairability

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stiffness increased as the weight percent of glass was increased. The deflection of the 50% glass specimens was only

50% of the deflection occurring in 0% glass specimens at the

same load and did not meet the minimum requirement of 2.0 mm

at a load of 5000 Gm in American Dental Association Specification No. 12. However, it does not seem that this reduced

deflection would detract from the material's suitability as

a denture base.

The transverse strengths of the materials (Table 3)

varied from a low of 5600 Gm for the 30% glass specimens

to 6300 Gm for the 50% glass specimens.

The significance of silane treatment of the glass powder

on transverse bending and strength may be seen by comparing

data in Table 3. The deflection of the specimens containing

glass which was not silane treated was about the same as

: I l that of specimens containing no glass. The transverse strengths

of specimens containing 30% untreated glass were 80% of the
23

values of those made with treated glass; at the 40% glass

level, they were only 67% as strong. This points out that

the simple addition of fillers to the matrix may cause a

deterioration of these properties. Without silane treatment, the glass particles weaken the material instead of

reinforcing it.

Repairability

Dentures are often subjected to forces

which cause fracture of the base material. The most common

repair materials are cold-curing resins because they are

quicker, easier and more economical to use, cause less

warpage of the base, and do not require the patient to

be without his denture for an extended period. Heat-cure

repairs are less common, more difficult to use, and may'

cause a warpage of the base material but do yield stronger

repairs. A cold-curing resin (without glass) and the

heat-cured resins containing glass were evaluated on the

30 and 40% glass-containing materials by means of transverse strength tests.

As can be seen in Table 3, the heat-cure repairs, using

identical materials to that from which the specimens themselves were made, had transverse strengths from 75 to 89%
24

of the strength of the original specimens. Those repaired

with the cold-cure resin had from 39 to 52% of their original

strengths. The denture base material containing no glass

when repaired with the cold-cure resin, had 55% of its

original strength. Therefore, when using a cold-cure repair

resin there was a greater reduction in the strength of the

repaired 30 and 40% glass materials as compared to repaired

denture base materials containing no glass. All failures

in the repair tests occurred at the interface between the

base and the repair material.

Indentation: The data in Table 4 summarize the results

of the indentation testing. The addition of glass resulted

in a greater resistance to indentation. The indentation of

50% glass specimens was about 80% as great as that on specimens containing no glass. However, the ability to recover

from the indentation was greater in the unfilled specimens

(88.2%) when compared to the glass-containing specimens

(80.6 to 84.2%). The net result is that the residual indentation is only slightly greater in the glass-containing

specimens. Therefore, the indentation left on a denture

by a piece of hard food would be about the same with all
Table 4•

Indentation

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of the materials. The 14 day storage in water had little

effect on the indentation and percent recovery.

Hardness ; There was no significant difference in the

hardness values as determined from the Rockwell Superficial

Hardness Tester using the 15W scale (Table 5). Water storage

for 2 weeks at 37°C lowered the hardness values only slightly.

Dens ity

The density of the four materials increased

as the relative percentage of glass was increased. The

values in Gm/cc were 1.19 for 0% specimens; 1.47 for 30%

specimens; 1.58 for 40% specimens, ahd 1.72 for 50% specimens. Thus, a denture made from the glass-containing ma-

!

! terials would be considerably heavier than one made from a

base containing no glass and could be objectionable from a

clinical standpoint.

Drop impact resistance: Fractures of denture base

materials commonly occur because the dentures are dropped,

thus subjecting them to impact forces. Therefore, the

measurement of the resistance of denture base materials to

this type of fracture is an important one. Drop impact testing

was selected in this study instead of the more commonly used

Izod impact test because the specimens are easier and more

25a

Table 5 • Rockwell Superficial Hardness*

Weight

of glass

Dry specimens

t

Wet specimens*

Hardness

number

S.D.* Hardness

number

S.D J

%

0 78.9 1.1 76.4 0.7

30 78.3 0.6 75.6 0.5

40 78.6 0.6 76.5 0.5

50 79.1 0.3 77.9 0.6

* 15W scale; a minor load of 3 kg was applied

and the dial gauge was set at 0. The major

load of 15 kg was applied for 15 ± 1 second

and the dial reading recorded. Two specimens

of each material were used and 5 tests were

made on each specimen

t Stored 7 days at 23 ± 2°C and 50 ± 10% relative

humidity

* Stored 14 days in water at 37°C

§ Standard deviation

number of values, x

n»Exs -(Zx) a

; n (n-1

)

any individual

where

value

n =
26

economical to make, they do not require machining, and the

specimen thickness is more representative of that which

actually exists in a denture.

The results of the drop impact testing are listed in

Table 6. When one considers the rather large deviations in

the results, it would appear that there is little difference

among the four materials as measured by this test? The

reasons for the large deviations in the results are not

known, but it could not be accounted for on the basis of the

differences in thickness of the specimens.

j I

Thermal expansion: The linear coefficients of thermal

expansion are listed in Table 7 and represent the average of

eight runs for each material. The coefficient decreases

as the amount of glass in the specimens is increased. This

could be expected since the coefficient of the glass is

about 7.0 x 10” 6 /° C (28 to 62°C) and that of the resin is

76.0 x 10” 6 (5 to 37°C). However, the decrease is not

linearly proportional to the volume percent of the glass

powder added to each material (calculated on an additive

basis) and is greater in each case. Evidently, the glass

powder acts to restrain the expansion of the resin matrix.
Table 6 • Drop impact tests

Weight

of glass

Mean failure

height*

Standard

deviat iont

% cm cm

0 57 11

30 57 16

40 52 14

50 50 10

* Mean height at which specimens failed when

subjected to a falling steel ball 20.64 mm

in diameter, weighing 35.77 Gm

10 , mean failure height = C + dEinj ± ^d

N

10 t Standard deviation = 1.62 d Zi 3 n t - N

linj

k n"

+ 0.029

Where C = normalized height of lowest line on

which a test is recorded

d = interval between drop heights

i = interval starting at 0 for the lowest

drop height at which a test is recorded

and increasing by one unit

n t = number failing or not failing at any

given interval

N = number failing or not failing
2 6b

Table 7 • Coefficients of linear thermal expansion

Weight

Coefficient of thermal

expansion*

of glass 5 - 3 7° C 37 - U

o O

r-'-

x 10" 6 S.D. t x 10 -6 S.D. t %

0 76.0 0.5 89.2 1.2

30 62.2 0.6 71.7 0.8

40 57.2 0.4 68 .0.8

50 49.9 0.5 57.8 0.7

* Determined by 4 tests on each of 2 specimens

for each material. Specimens 203 x 11.1 x

11.1 mm (8 x 7/16 x 7/16 inch)

t Standard deviation =

\ number of values, x

-

n • Ix 3-(Zx) 3

; where n =

n (n-1

)

any individual value

r
27

The coefficients were higher in the 37 to 70°C range

for all four materials. In a previous study it was found

that resin denture base materials containing 14 and 21% by

weight of glass fibers had lower coefficients at the higher

temperature ranges presumably because the fibers restrained

the expansion more at higher ranges than at the lower ranges.

11

This was not the case with the silane-treated glass powders

(Table 7). One of the specimens, tested again after storage

in water for 23 days, had a coefficient equal to those obtained

after seven days storage in water.

The importance of the differences in thermal expansion

on the fit of clinical dentures would not be significant.

In a previous study, neither the patient nor the dentist could

detect disparities in the fit of dentures having such small

magnitudes of differences as would be caused by the differences

in thermal expansions of these materials. 13

The importance of the lower coefficients of thermal

expansion may be significant in attempting to bond porcelain

denture teeth to the resin-glass composite denture base by

means of appropriate silane coupling agents. Results will be

presented in a subsequent report. 3
Resistance to deformation: The resistance to

deformation from different types of applied forces is

seen In Table 8 which lists the values for various

moduli for each material. The modulus with each type

of loading can be seen to increase twith increasing

amounts of glass. The effect of storage in water for

21 days appears to be negligible in the case of Young's

modulus as determined by the sonic method.

Whether such added resistance to deformation is an

advantage or is, in fact, desirable is not known. It is

believed by some dentists that denture bases should be

somewhat flexible since they might cause less injury

to the underlying oral structures. Added stiffness

might be a factor in attempts to bond silane treated

porcelain teeth to the denture base.
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29

Glass solubility: The 24-hour water solubilities of the

glass powders both silane treated and as received were 0.24%

and 0.30% respectively and that of the powdered porcelain

teeth was 0.06%. The relative inertness of porcelain teeth

in the oral environment has been well established by long

periods of clinical usage and points out the severe nature

of this solubility test. The solubility of the silane

treated glass powders for periods up to five days as shown

in Figure 3 was 0.55%.

! I

|

The results of the spectrochemical analysis of the 24

hour residues are listed in Table 9. The major constituents

i

I | found in the residue from the reinforcing glass powder were

aluminum, calcium, silicon, and barium. The origin of the

calcium is uncertain since it was not in the nominal batch

composition. It may be from impurities present in the original

glass or from the method of sampling the residues that remained

in the glass weighing bottles. The discrepancies in the amounts

of certain elements such as boron and aluminum in columns 1

and 2 in Table 9 is probably attributable to experimental error.

29a

Table 9 • Results of the spectrochemlcal analysis of the residues obtained from the glass and porcelain 24 hr solubility tests

Element

M<iterials Tested

Silane

Treated

Glass

Untreated

Glass

Porcelain

Teeth

Compos it ion bv Weight

Ag

% %

t A1 1-10 .1-1 m

As - - - Au - - -

B .1-1 1-10 M

Ba >10 >10 ? Be - - - Bi - - - Ca 1-10 1-10 m

Cd - - - Ce - - - Co ? ? - Cr .001-. 01 ? ? Cu .01-.

.01-.

m

Fe .01-.

.001-. 01 m

Gel - - - Ge - - - Hf - - - Hg - - - In - - - Ir - - - KLa _ _ M

Mg .1-1 .1-1 m Mn .001-. 01 .001-. 01 - MO - - - Na .1-1 .1-1 M

Nb - - - Ni .01-.

? - Os - - - P - - - Pb - - - Pd - - - Pt - - - Rh - - - Ru - - - Sb - - - Sc - - - Si 1-10 1-10 M

Sn - - - Sr .1-1 .1-1 - Ta - - - Te - - Th - - - Ti ? ? - T1 - - - U - - - V - - - W - - - Y - - - Zn .1-1 .1-1 - Zr “ “

- Not detected

t Trace noted

m Minor constituent

M Major constituent

? Detection uncertain
30

Aluminum, calcium, and silicon are relatively innocuous

elements and would present no problem of toxicity. However,

water soluble salts of barium, notably BaCl 2 and BaN03 are

extremely toxic. The lethal dose of the chloride is not

known but has been reported to be as low as 0.8 to 0.9 Gm.

The toxicity of BaF a may be about the same as that of NaF in

man.

14 ’ 16 Whether enough soluble barium salts could be absorbed from the denture materials to present a toxicity hazard

is not known. However, the water solubility of the radiopaque

composite denture base material is very low (Table 2).

Summary and conclusions

Physical properties were determined for radiopaque

composite denture base materials composed essentially of

poly (methyl methacrylate) as the matrix and 30, 40, and 50%

by weight of a silane-treated glass powder as the reinforcing

filler. The poly (methyl methacrylate) without glass was

included for comparison.

All of the materials complied with the requirements of

American Dental Association Specification No. 12 for Denture

Base Polymer except that the transverse bend specimens containing 50% glass were too stiff for the minimum deflection

requirement at a 5000 Gm load.
31

There was little or no difference among the four materials

in hardness, indentation and recovery, water sorption, and

color stability. The solubility of the glass-containing specimens was slightly greater than that of the specimens containing

no glass. The addition of glass extended the time required

to reach the packing stage.

The addition of 30% glass to the resin caused a slight

reduction in transverse strength while the addition of 50%

glass slightly increased the transverse strength; addition

of 40% glass yielded specimens having transverse strength

equal to that of the resin with no glass. The strength of

specimens made with glass that had not been treated with

silane was significantly lower.

The materials were repairable by commonly used methods.

The use of heat-cure repairs gave higher strengths than

cold-cure repairs.

The density of the glass-containing materials was

significantly greater and would result in heavier dentures

that might be objectionable clinically.

T
32

The drop impact resistance as measured by a falling steel

ball indicates that there was little difference among the four

compos it ions

The coefficients of linear thermal expansion were decreased by addition of the glass but the decrease would not

be large enough to visibly affect the clinical fit of dentures.

Young's, bulk, shear, and flexural moduli was all increased

as the amount of glass was increased. This would result in

dentures having a greater resistance to deformation from the

various types of stress.

The 24-hour water solubility of the glass powder was

0.24% and about 4 times that of powdered porcelain teeth. The

major soluble constituents of the glass powder were barium,

calcium, aluminum, and silicon. Solubility of the silanetreated glass powder increased to about 0.55% after 5 days.

However, the water solubility of the radiopaque composite

denture base material (resin plus radiopaque, silane-treated,

powdered glass) was very low.

Within the foregoing limitations it is believed that an

acceptable radiopaque denture base composite material has

been described.
33

Bibliography

1. Chandler, H. H.; Bowen, R. L., and Paf f enbarger , G. C.

The need for radiopaque denture base materials: A

review of the literature. (submitted to The Journal

of Biomedical Materials Research)

.

2. Chandler, H. H. ? Bowen, R. L., and Paf f enbarger , G. C.

Development of a radiopaque denture base material,

(submitted to The Journal of Biomedical Materials

Research)

.

3. Chandler, H. H. ; Bowen, R. L., and Paf f enbarger , G. C.

Radiopaque denture base materials: Technic dentures,

(submitted to The Journal of Biomedical Materials

Research)

.

4. Bowen, R. L., and Cleek, G. W. X-ray-Opaque Reinforcing

Fillers for Composite Materials. J Dent Res 48:79

Jan-Feb 1969.

5. American Dental Association Specification No. 12 for

Denture Base Polymer. Guide to Dental Materials and

Devices Fourth Edition (1968-1969) , American Dental

Association, Chicago, Illinois, p. 155.
3 4-

7.

8 .

9.

10 .

Stanford, J. W. ; Burns, C. L., and Paf f enbarger , G. C.

Self-curing resin for repairing dentures: S®me physical

properties. JADA 51:307 Sept 1955.

American Dental Association Specification No. 15 for

Acrylic Resin Teeth. Guide to Dental Materials and

Devices (1968-1969) , Fourth Edition American Dental Association Chicago, Illinois, p. 164.

Cornell, J. A., Tucker, J. L., and Powders, C. M.

Physical properties of denture-base materials.

J Pros Dent 10:516 May 1960.

Tentative method of test for drop impact resistance

of polyethylene blow-molded containers ASTM Designation

D2463-65T. 1969 Book of ASTM Standards with related

material 26:588 June 1969. Published by American

Society for Testing and Materials Philadelphia, Pa.

Dixon, W. J. , and Massey, F. J., Jr. Introduct ion

to Statistical Analysis, Second Edition ^ McGraw-Hill

Book Co., Inc • i New York) 1957, chapter 19.
35

11. Woelfel, J. B.; Paf fenbarger , G. C., and Sweeney, W. T

Some physical properties of organic denture base

materials. JADA 67:489 Oct. 1969.

12. Dickson, G., and Oglesby, P. L. Elastic constants of

dental amalgam. J Dent Res 46:1475 Nov-Dec 1967.

13. Woelfel, J. B . ; Paf fenbarger , G. C., and Sweeney, W. T

Changes in dentures during storage in water and in

service. JADA 62:643 June 1961.

14. Sollman, T. A Manual of Pharmacology Eighth Edition.

Philadelphia, W. B. Saunders, Co., 1957, p. 666.

15. Gleason, M. N.; Hodge, H. C.; Smith, R. P., and

Gosselin, R. E. Clinical Toxicology of Commercial

Products Third Edition . Baltimore, The Williams and

Wilkins Co., 1969, Section II, page 21; Section III,

page 43
Legends

Fig 1

Fig 2

Fig 3

Apparatus for measuring drop impact resistance.

A, channel for directing the falling ball; B,

ball catcher; C, specimen holder; D, specimen;

E, steel ball, 20.64 mm in diameter.

Higher magnification of the specimen holder

seen in Fig. 1. Distance AB = 3.43 mm; BC =

3.17 mm; AD = 38.1 mm.

Cumulative percent glass dissolved in a mixture

containing 10% by weight of the silane treated

glass and water.

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