NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT

31 1.05- 11-31 1056 1 June 30, 1970

NBS REPORT

10 274

Progress Report

on RADIOPAQUE DENTURE BASE MATERIALS

TECHNIC DENTURES

by + f

H. H. Chandler,* R. L. Bowen and G. C. Paffenbarger

* Research Associate, American Dental Association Research Program

at the National Bureau of Standards, Dental Research Section,

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 D E 02 74 2—0 1 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 Administration

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on October 9, 2015.

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U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
[rrr[rccc[[[ccc[c
RADIOPAQUE DENTURE BASE MATERIALS

TECHNIC DENTURES

ABSTRACT

Technic dentures were made using composite base materials

containing 30, 40 and 50 weight percent of a silane-treated,

radiopaque, powdered glass as the reinforcing filler and

poly (methyl methacrylate) as the matrix. Dentures containing no glass were included for comparison. Molar-to-molar

dimensional changes, effects of silane treatment of the

porcelain teeth and handling and finishing characteristics

were determined.

Dentures containing glass had less dimensional change

during curing and subsequent water storage than those without

glass. Thick upper dentures exhibited the least change and

thin lowers, the most. The differences in the magnitudes of

the changes would not be clinically noticeable.

Silane treatment of the porcelain teeth in thick upper

dentures resulted in breakage of the posterior teeth in

almost all instances. Posterior teeth also fractured in

thick upper dentures containing 40 and 50% of the silanetreated glass even though the teeth were not treated with

silane

.
2

Mixing and molding properties of the composite materials,

while acceptable, were slightly inferior to the material

containing no glass. Finishing characteristics were definitely inferior in that it was more difficult and timeconsuming to attain the final surfaces and these surfaces

were not as smooth as those in dentures without glass.
3

RADIOPAQUE DENTURE BASE MATERIALS:

TECHNIC DENTURES

Introduction

A previous report described the need for esthetically

acceptable radiopaque denture base materials. 1 It was

established in a review of 123 cases of ingested and aspirated dentures and fragments that radiographic localization of the foreign bodies often would have been facilitated

if the base material had been radiopaque.

Another report described the development of an experimental denture base material based on the addition of a

radiopaque, silane-treated glass powder to poly (methyl

methacrylate) ( PKMA)

.

2 Other resin-glass combinations

were investigated but the above material appeared to offer

the best combination of properties for immediate development.

Specimens containing from 29 to 57 weight percent of the

glass filler had sufficient radiopacity to be of aid in

localization of denture foreign bodies.
4

y

Subsequently, pertinent physical properties of denture base

materials composed essentially of PMMA and 0, 30, 40, and 50

weight percent of the radiopaque glass powder were reported. 3

In the present study twenty technic dentures were made

of the foregoing materials to determine the molar-to-molar

dimensional change during processing and water storage; the

effects of silane treatment of porcelain teeth when used with

composite materials of these types, and the mixing, molding,

and finishing characteristics during denture fabrication.

methods* Materials and *

1 .

The following materials were used in

Liquid - The monomer liquid was 98.5%

(Rohm and Haas Co.) and 1.5% ethylene

(Borden, Inc) by weight.

making the dentures;

methyl methacrylate

dimethacrylate

* 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.
5

2. Powder - The powder was 95.0% PMMA and 5.0% dibutyl

phthalate by weight (Esschem Co., Div. of Sartomer

Resins, Inc. Type #P5-69-203).

3. Glass fillers: Filler A - A silane-treated powdered

glass (Corning Glass Works, Code X816JL) that was

elutriated before use in an attempt to remove the smallest

particles. It had a batch formulation as follows: Si02/

44; BaF 2 , 28; B 2 03 , 16; and Al 2 03 , 12, in mole percent. 4

The powder particle sizes ranged from about 1 to 50 pm.

The silane treatment and elutriation procedure have been

described previously .

Filler B - Two dentures were made using Filler B after

it had been washed in an attempt to remove any excess

silane. The washing was carried out by making a thin

slurry of the powder in 95% ethanol. The slurry was

vigorously shaken for several minutes and then vacuum

filtered. This process was repeated using absolute

ethanol, and finally acetone. The powder was dried and

passed through a U. S. Standard Sieve No. 100 to remove

any lumps of caked or agglomerated material.
6

Filler C - One denture was made with the glass as received

without silane treatment or elutriation.

4. Pigment and opacifier - Most of the dentures were pigmented with cadmium red (United Color and Pigment Co.) and

opacified with titanium oxide (Fisher Scientific Co.).

5. Silane (Union Carbide A174 Silane) - Fillers A and B and

some of the porcelain denture teeth were treated with a

silane coupling agent to promote bonding to the resin of

the base material. One denture was made with the monomer

liquid to which was added 3% by weight of the unhydrolyzed

silane

.

6. Porcelain teeth - Technic teeth (Trubyte Bioform -

mold 42-F with Pilkington Turner Posteriors, Dentsply

Internat ionaf f Inc . ) were used in the dentures made for

the purpose of measuring molar-to-molar dimensional

change. Regular clinical teeth of the same mold were

used in the dentures made to study the effects of silane

treatment of the teeth.
7

The dentures tested contained either 0 , 30, 40, or 50

weight percent of the radiopaque glass- The composition of

the mix for each glass content was reported previously.^

Twelve complete dentures with either no filler or

Filler A were made to determine the molar-to-molar dimensional change occurring during processing and subsequent

water storage. The dentures were of three different types;

a thick upper, a thick lower, and a thin lower for each of

the four glass levels; the volume of the base material in

each denture type was approximately 20, 25, and 11 ml,

respectively

.

The gypsum casts and wax models for each denture type

were made in the same rubber molds to ensure nearly exact

duplications- Dental stone was used for pouring the casts

and for all flasking procedures. Wax was removed by the

customary boil-out techniques after which the teeth and

flasks were thoroughly cleansed with boiling water followed

with chloroform. All dentures were cured at 73°C for 9

hours and allowed to cool in the curing bath to room temperature .
8

The method for determining the molar-to-molar dimensional change has been employed previously. 0 Basically,

it involved measurement of the distance between reference

marks on the ends of stainless steel pins that had been

cemented in the occlusal surfaces of the second molar denture

teeth. The measurements were made at 23 ± 1°C with a measuring

microscope and recorded to the nearest 0.0025 mm at the following stages: waxed denture flasked to the occlusal surfaces;

cured denture deflasked to the occlusal; denture removed

from cast; denture finished and stored in water for one

week, and denture stored in water for one month.

Eight additional thick upper dentures were made to

determine the effect of silane treatment of clinical porcelain

teeth in dentures made with fillers A, B, and C- The teeth

that were silane-treated and the fillers are listed in Table 1.

The teeth were prepared for silane treatment by washing

with a boiling solution of detergent in water followed by a

thoroughr inse with boiling distilled water. A 0 . 5% solution

of the silane in distilled water was acidified to pH 3-4 with
9

glacial acetic acid and stirred for one hour. The cleaned

teeth were placed in the solution for 30 minutes, drained,

and baked at 110°C for 15 minutes. The above treatment was

carried out before wax-up of the dentures. Flasking', packing,

curing, and finishing were carried out in the usual manner

except that extreme care was exercised to ensure that the

teeth were completely cleaned during the boil-out procedure.

Chloroform was not used.

After finishing, all twenty dentures were inspected

for broken teeth. The dentures were then temperature

cycled by placing them in 5°C water for 5 minutes followed

by immersion in 55°C water for 5 minutes. This cycle was

repeated 5 times after which the dentures were again inspected for broken teeth. The twelve dentures made for

measuring molar-to-molar dimensional change were not temperature cycled until all measurements had been completed.

Results and discussion ^

Molar-to-molar dimensional change : The values for the

molar-to-molar dimensional changes as determined at the various

stages may be seen in Figure 1. Each point on the graph
10

represents the average percent dimensional change for the

thick upper, thick lower, and thin lower dentures made with

each material. The magnitudes of the overall changes range

from - 0 . 32% for the 0% glass dentures to -0.24% for the 50%

glass dentures. Such differences might be expected due to

the lower coefficients of thermal expansion of the glasscontaining materials. 3

The greatest contraction occurred with the thin lower

dentures and the least with the thick upper dentures. For

example, the thin lower dentures containing 40% glass contracted

0.50% and the thick upper dentures containing 40% glass contracted

0.19%. Evidently, denture thickness and shape can act to restrict

the contractural forces. The greatest contraction occurred

when the dentures were removed from the casts. Prior to

removal, the contraction was restricted by the cast and

flasking stone. After finishing, the dentures continued

to contract probably because of continuing stress relief,

but soon began to expand due to water sorption.

The overall differences among the four materials was

only slight and probably would have no clinical significance.

A previous investigation6 has shown that the molar-to-molar
11

linear dimension of heat-cured PMMA complete technic dentures

will decrease about 0.45 to 0.55 percent during curing. Most

of this change can be attributed to the thermal contraction

that occurs when the dentures are cooled from curing temperature to room temperature. Part of the contraction is compensated for by the subsequent expansion that occurs due to

water sorption and thermal expansion when the denture is

inserted in the mouth. The overall dimensional change can be

expected to be a slight shrinkage with the heat-cured PMMA

type resins. Subsequent changes that do occur are not

clinically noticeable because the adaptability and change in

the supporting tissues is of much greater magnitude. 5 Nonetheless / it can be assumed that the more nearly the overall

dimensional change approaches zero, the better the denture

will duplicate the impression.

Silane treatment of porcelain teeth : The advantages

of constructing dentures in which the porcelain teeth are

bonded to the base materials are well recognized. One advantage of such bonding is the prevention of seepage of

oral fluids into the crevice between the teeth and the base

material. 0 These fluids cause the development of stains
12

and odors which contribute to poor denture hygiene. Another

advantage may be a strengthening of the denture0 by effectively

increasing its cross-sectional area. Bonding would eliminate

the notches in the resin due to unbonded teeth, and thus some

of the stress concentrations that occur in these areas from

notch effects.

Such bonding is made possible by applying an appropriate

silane coupling agent to the teeth before curing the denture.'

However, the effects of the bonding are such that stresses are

introduced into the teeth resulting in severe weakening or

fracture. These stresses arise as a result of the differential

in thermal expansion when bonding occurs between the resin base

materials [70 - 116 x 10 _6 /°C (37-70°C)] y and the porcelain teeth

[8.0 x 10 -o /°C (30-400°C)

]

1

0

. Therefore, silane treatment has

not become a clinically acceptable procedure for posterior teeth.

Because of the lower coefficients of thermal expansion

of the composite bases used in this investigation [ 58 - 72 x

10 _b /°C (27-70°C)], 3 it was hoped that porcelain teeth might

be bonded to the base materials without weakening or fracturing

of the teeth.
13

However, when the teeth on the right side of the dentures were

silane treated, the posterior teeth on that side fractured in

almost all cases (Table 1, dentures 1-4). The fractures of

the posterior teeth occurred in a mesial-distal direction in

the central grooves in all cases (Fig. 2). (No breakage of

anterior teeth occurred in any of the dentures made in this investigation or in another investigation.*3

) In addition it was

noted that in the 40 and 50% glass-containing dentures (Table 1,

dentures 3-4) numerous teeth fractured that had not been

silane treated. An examination of the twelve dentures made for

measuring molar-to-molar dimensional change showed that seven

out of eight of the posterior technic teeth in the 50% glass,

thick upper denture were broken although the teeth had not

been silane treated. This suggested that there might have been

excess silane in the glass powder from its original silane

treatment and that this was effective in bonding the teeth to

the base, thereby causing the unexpected tooth breakage.

To determine if washing the glass before use would

prevent tooth breakage, two dentures were made with Filler B

(washed) . One of these dentures was made without any of the
14

teeth silane treated (Table 1, denture 5) and one with all

the teeth silane treated (Table 1, denture 6). Most of the

posterior teeth fractured, especially after temperature

cycling, in both dentures. Perhaps the washing procedure

was not effective in removing the excess silane and this

may have allowed some to migrate to the surface of the porcelain teeth. It is also possible that the higher moduli’ of

the materials containing silane-treated glass contributed

to the stresses applied to the teeth.

There were no fractured teeth in the denture made with

glass that had not been silane treated (Filler C), Table 1,

denture 7. Placement of 3% by weight of the silane in the

monomer also did not result in fractured teeth (Table 1,

denture 8 )

.

Many of the dentures were sectioned by making a cut

along the tissue surface of the posterior ridge area as deep

as possible without touching the teeth. The base material

buccal to the posterior teeth was then fractured away. When

this was done in those dentures containing fractured teeth,

many of the teeth were observed to have fractured into
15

numerous pieces with some of the fragments adhering

securely to the base material as in Figure 3. In sectioning the denture made with untreated glass the teeth could

be removed easily with no apparent adhesion or tooth damage

(Fig. 4)

Mixing, handling, and finishing properties : In making

mixes containing the reinforcing glass filler, there was a

tendency for the glass to settle to the bottom of the

mixing vessel. In order to obtain an even distribution of

the glass, it was necessary to stir the materials more often

than would be done for a mix containing no glass, especially

during the early stages when the mix was relatively fluid.

When the liquid was added to the powders, it appeared

at first that the mix was too dry, but with continued

stirring, it became fluid enough to ensure proper wetting

of the polymer beads.

The molding characteristics of the glass containing

materials were similar to those with no glass. However

,

they did not seem to flow quite as readily under similar

flasking pressures. In addition, the glass-containing
16

materials (especially 50% mixes) tended to adhere slightly

to the flasking stone and polyethylene separating sheets.

Alginate mold lining compounds worked well with these materials .

Finishing of the glass-containing dentures was more

difficult and time-consuming, but could be accomplished

using accepted techniques. Shaping and trimming the

gingival areas was especially difficult and time-consuming

because the material tended to adhere to the porcelain

teeth and did not cut easily with hand finishing instruments. Finishing procedures using a wet rag wheel and

pumice were also time-consuming because deep scratches

rag

were hard to remove. Final polishing with a dry/wheel and

a polishing agent did not produce as glossy a finish as

that obtained on the dentures without glass.

Summary and conclusions

Twenty technic dentures were constructed of base materials containing 0, 30, 40, or 50 weight percent of a

silane-treated, radiopaque glass powder as the reinforcing

filler and poly (methyl methacrylate) as the resin matrix.
17

The overall average molar-to-molar dimensional

change of three dentures for each material ranged from

-0.24 for the 50% glass-containing dentures to -0.32

for those containing no glass. The greatest change

occurred in thin lower dentures with no glass and the

least in thick upper dentures with 50% glass. The

addition of glass reduced the overall dimensional change,

but the amounts would not be clinically noticeable by

the patient or the dentist.

Although the coefficient of linear thermal expansion

of the glass-containing materials is significantly less

than materials containing no glass, 3 it did not prevent

the breakage of posterior porcelain teeth that had been

silane bonded to the base materials. In addition, there

was considerable breakage of posterior teeth in thick

upper dentures containing the higher percentages of silanetreated glass even though the teeth were not intentionally

silane treated. Washing the treated glass with ethanol and

acetone before use was not successful in preventing tooth

breakage. There were no broken teeth in the denture made with
18

glass that had not been silane treated and there was no

instance of fracture of any anterior teeth in any of the

dentures

.

It was demonstrated in a previous paper that the

greatest need for radiopaque denture base materials was

in maxillary partials consisting of a resin palate to which

is attached one or more anterior teeth. x Since there

usually is no labial flange in these partials, one might

expect very low stresses to be applied to the teeth even

when they are silane bonded to the base material. If

posterior teeth with a buccal flange are present, then

fracture or weakening of the teeth is probable. An

alternative would be to use radiopaque acrylic resin

teeth bonded to the composite denture base.

Mixing and molding characteristics of the glasscontaining materials, while acceptable, were slightly

inferior to the material containing no glass. Finishing

characteristics were definitely inferior in that it

was more difficult and time-consuming to attain the final

surface and this surface was not as smooth as in dentures

containing no glass.
19

TABLE 1

FRACTURING OF PORCELAIN TEETH IN DENTURES

Denture

No . * Teeth Silane

Treated

Filler Used Fractured Teeth

Before Cycling*

Fractured Teeth

After Cycling 4-

1 2-8* None 2-5* 2-5*

2 2-8 30% Filler A 2,4 2-4

3 2-8 40% Filler A 2-5, 13, 14 2-5, 13, 14

4 2-8 50% Filler A 2-5, 13-15 2-5, 13-15

5 None 50% Filler B 4, 12, 14 2-5, 12-14

6 All 50% iller B 2, 3, 4, 14 2-5, 13-15

7 None 50% Filler C None None

8

None

3% Silane

in monomer

None None None

* All dentures were thick uppers

t Cycling consisted of immersing the entire denture in 5°C water

for five minutes followed by immediate insertion in 55° C water

for five minutes. The cycle was repeated five times.

1 Tooth numbers refer to those in the system adopted by the Council

on Dental Education of the American Dental Association whereby

tooth number 4 the upper right 3rd molar, tooth number 16 is the

upper left 3rd molar, tooth number 17 is the lower left 3rd molar,

and tooth number 32 is the lower right 3rd molar. Porcelain

teeth corresponding to numbers 1 and 16 were absent.
20

Bibliography

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

Development of a radiopaque denture base material: A

review of the literature. (submitted to The Journal of

the American Dental Association)

2. Chandler, H. H. ; Bowen, R. L., and Paf fenbarger , G. C.

Development of a radiopaque denture base material.

(in manuscript)

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

radiopaque

Physical properties of a/denture base material. (in

manuscr ipt

)

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

Dimensional changes occurring in dentures during processing.

JADA 61:413 Oct 1960.

6. Paf fenbarger , G. C. ; Sweeney, W. Timothy, and Bowen, R. L.

Bonding porcelain teeth to acrylic resin denture bases.

JADA 74:1018 April 1967.
21

7. Semmelman, J. Q. # and Kulp, P. R. Silane bonding porcelain

teeth to acrylic. JADA 76:69 Jan 1968.

8. Myerson, R. L. Effects of silane bonding of acrylic

resins to porcelain on porcelain structure. JADA 78:113

Jan 1969.

9. Woelfel, J. B.; Paf f enbarger , G. C., and Sweeney, W. T.

Some physical properties of organic denture base materials.

JADA 67:489 Oct 1963.

10.

Sacchi, H., and Paf f enbarger , G. C. Simple technic for

making porcelain jacket crowns. JADA 54:366 March 1957.
Legends

Fig 1

Fig 2

Fig 3

Fig 4

Average molar-to-molar dimensional change of technic

dentures. Each point represents the average percent

change for a thick upper, a thick lower, and a thin

lower denture for each material.

A section cut from a 40% glass complete upper denture

showing mesiodistal fractures in the central groove

of the posterior teeth. The teeth were silane treated.

Section removed from a 40% glass denture showing

the numerous fractures that occurred upon removal

of the bulk of the teeth leaving some portions

securely attached to the base material.

Section removed from a 50% glass denture in which

the glass had not been silane treated. The teeth

show no evidence of bonding to the base material.

if

USCOMM-NBS-DC
AVERAGE

LINEAR

DIMENSIONAL

CHANGE

IN

PERCENT

4 ©.1

x —x no glass

o—o 3 0% 9 lass — 40% 9 1 ass

*—* 50% glass

- 0.4

^ wax u red ^cu red Polished one

denture denture clenture ^ Plus month

f I as ked d ef Sasked removed one week in

t o t o from i n wat e r occ 1 y saS occ 1 u sa

1

cast water

KM