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NATIONAL BUREAU OF STANDARDS REPORTN'SS PROJECT NBS REPORT
0708-20-07560 December 31, 1959 669O
Progress Report
on
THERMAL EXPANSION OF DENTURE BASE RESINS
by
Ruth M. Davenport*George Dickson**
* Physical Science Aid, Dental Research Section,National Bureau of Standards.
** Physicist, Dental Research Section, NationalBureau of Standards.
This work is a part of the dental research program conduc-ted at the National Bureau of Standards in cooperationwith the Council on Dental Research of the American DentalAssociation, the Army Dental Corps, the Dental SciencesDivision of the School of Aviation Medicine, USAF, theNavy Dental Corps, and the Veterans Administration.
IMPORTANT NOTICE
NATIONAL BUREAU OF ST/
intended for use within the 1
to additional evaluation and r
listing of this Report, either i
the Office of the Director, Na
however, by the Government
to reproduce additional copie.
Approved for public release by the
director of the National Institute of
Standards and Technology (NIST)
on October 9, 2015
rogress accounting documents
mally published it is subjected
reproduction, or open-literature
ion is obtained in writing from
Such permission is not needed,
prepared if that agency v/ishes
U. S. DEPARTMENT OF COMMERCE
NATIONAL BUREAU OF STANDARDS
THERMAL EXPANSION OF DENTURE BASE RESINS
Abstract
Thermal expansion measurements were made on
eleven denture base materials and one sample of
commercial Lucite rod. Measurements were made
over a temperature range from approximately
20°C to 70°C ( 68° - 158°F) using the fused-
quartz tube apparatus. The materials were run
dry and then after having been stored in water
at either 37°C (98.6°F) or 68 °C (154. 4°F) for
several days, they were run wet. The dimensions
of the molded specimens were approximately 8
inches by 7/l6 inch by j/l6 inch. The results
show that coefficients of thermal expansion
of the methyl methacrylate denture base resins
over the 20°C (68 °F) to 70°C (158°F) range
averaged near the approximately 90 x 10~6 per
°C obtained for commercial Lucite rod . The
coefficients for vinyl copolymer, epoxy, and
styrene denture resins were approximately
10, 15 and 25 percent respectively below the
average for the methyl methacrylate materials.
Methyl methacrylate resins containing large
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amounts of glass fiber had cofficients over
50 percent lower than the average of those
of the other methyl methacrylate resins.
Soaking in water at elevated temperatures for
several days raised the coefficients of meth-
acrylate materials by approximately 10 to 20
percent
.
1 . INTRODUCTION
In the field of dentistry, where dimensional accuracy
is essential, thermal expansion is a very Important prop-
erty. In spite of this, little information has been
published on the expansion of dental materials, particu-
larly those which have been developed during the past
ten years.
Some data are available on the expansion of the basic
components of the various denture base resins [1]; that
is, on methyl methacrylate, acrylics, styrenes, vinyls,
epoxys, and various copolymers but little has been done
to relate these values to dental materials as they appear
on the market. A search of the information provided with
the denture base materials studied disclosed that only
one listed thermal expansion among the physical properties
for which data were given.
This study was undertaken to obtain data on the
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linear thermal expansion of denture base resins between room
temperature and approximately 70°C (158°F).
2. MATERIALS AND EQUIPMENT
Included in the group of denture base materials studied
(Table l) were self-curing and heat-curing methyl meth-
acrylates^ filled methyl methacrylate, vinyl-acrylic co-
polymer, styrene, and epoxy resins. Measurements were
also made on one specimen of commercial Lucite rod. The
recommended methods of processing the denture base mate-
rials included Injection and compression molding, "dry"
and "wet" curing, and short and long curing cycles.
The fused quartz expansion apparatus (Figure l) was
essentially that described by Hidnert and Sweeney [2]
and later modified by Hidnert [3]. A water jacket sur-
rounding the fused quartz tube was used to control the
temperature of the specimens. Water at temperatures
from room temperature to 70°C was passed through the jacket
by means of a Precision Scientific Company circulating
water bath. Temperatures below room temperature were
obtained by passing tap water through cooling coils in
an ice bath and then through the water jacket.
3 . PROCEDURE
Most of the thermal expansion specimens were made
by mixing and curing the material according to the
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manufacturers ' directions. One "unit" of material was
sufficient to mold a bar specimen 8 inches x 7/l6 inch
X 7/16 inch in the brass mold shown in Figure 2, The
mold, with overall dimensions of 9 1/2 inches x 3 1/2 inches
X 7/i 6 inch, was filled with resin, placed in a Carver
Press under a load of 5^000 pounds, and held there for
the length of time recommended to effect a cure. In
those cases where heat was needed, the press platens
were heated to the recommended temperature before the
mold was placed in position and then the whole assembly
was held at this temperature for the proper length of
time, usually 6 to 8 hours, after which the heat was
turned off and the specimen allowed to cool in the press
over night. The specimen was then removed from the mold,
the edges smoothed, and the length of the specimen
measured
.
The specimen of commercial rod was as received
except for length, and the specimen of Vernonite Gel
was cut from a block which had been cast at the Vernon-
Benshoff Company in 1948. The specimen of Jectron was
obtained from a local supply house and turned down to the
proper diameter, but it was approximately 2 inches shorter
than the rest of the specimens. Specimens were conditioned
at a temperature of 23° ± 1°C (73.4 ± 1.8°F) and relative
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humidity of 50 ± 4 percent for at least 2 or 3 days prior
to being run in the thermal expansion apparatus.
To obtain thermal expansion data the specimen of
resin was placed in the fused-quartz tube and the quartz
plunger was placed on top of it. This assembly was then
inserted into the water jacket and the dial indicator
adjusted on the top of the quartz plunger. When the
temperature in the water jacket and the specimen had
reached the minimum desired (usually about 15 “C), initial
readings of the gauge and the thermometer were taken.
From this pointy the temperature was raised in approxi-
mately 10°C (i8°F) intervals to 49°C (120°F) and in
approximately 5°C (9'^F) intervals from 49°C to 70°C
(120° - 158°F). It was found that about 45 minutes
was a sufficient time to reach equilibrium at each
temperature as evidenced by cessation of movement of the
indicator. Readings of the dial indicator and the ther-
mometer in the water jacket were recorded at equilibrium,,
the temperature was raised to the next equilibrium
point and the process was continued until the top
temperature was reached. Temperature rise was controlled
by a thermoregulator in the circulating water bath.
After being heated the specimens were allowed to
cool down overnight in the apparatus and were run again.
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This was repeated at least once more. After the runs
described above had been completed, the specimens
were removed from the apparatus and allowed to remain
in air at a temperature of 23° ± 1°C (73.^ - 1.8°F) and
a relative humidity of ^0 ± h percent. Some time later
one specimen of each material (with one exception)
was conditioned in water at 37°C (98.6°F) or 68°C
(154.,4°F) for at least one week and then placed in
water in the quartz tube and the procedure described
above repeated. In addition to the above procedure
the specimen of Lucite was dried in an oven after
being run wet and was then re-run in the dry condition.
This specimen was weighed before and after conditioning
treatments in order to determine the change in water
content
.
Curves of the form y = a -i- bx -i- cx^ + dx^ were
fitted to the data by the method of least squares
using an IBM 704 computer. Figure 3 shows the calcu-
lated curves and experimental points for three runs
(dry) of Lucite. The computer provided values of y
corresponding to the selected values of x = 20, 27 ,
37^ and 70°C (68, 80.6, 98.6 and 158°F) from these
curves. From these values, coefficients of linear
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thermal expansion from either 20°C (68°F) or 2J°C (80.6°F)
to 37°C (98.6°F), from 37°C (98.6°F) to 70°C (158°F) and from
either 20° or 27° to J0°C were calculated for each run.
Average coefficients for each specimen were then obtained
by averaging the values for two or more runs.
4. RESULTS AND DISCUSSION
Average coefficients for all of the materials In
both "dry" and "wet" condition, are given In Table 2.
The curves shown In Figure 4 also show average "dry" ex-
pansion of all resins Included In this study. These
curves were obtained by averaging, for each material,
the ordinates of the calculated curves for the Individual
runs and converting the averages to percent change In
length
.
Reproducibility of the results for repeated runs of
the same specimen Is Indicated by the standard deviations
given In Table 2. Ip some Instances, results obtained
on the first run differed greatly from those obtained
on later runs. Such erratic results, which may be caused
by slight changes In position of the specimen during the
first heating In the apparatus, were eliminated from the
averages reported.
In comparison with other denture base materials, the
methyl methacrylates show slight higher average coefficients.
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The coefficients for vinyl-acrylic, epoxy, and styrene
resins were approximately 10, 15 and 25 percent lower, re-
spectively, than the average of the methyl methacrylate values.
Methyl methacrylate resins containing large amounts of glass
fiber as filler had coefficients 50 percent or more lower
than those of the other methacrylate materials.
Comparison of the thermal expansion values below
and above 37°C (98.6°F) shows that all of the materials,
with the exception of the glass-filled resins, have
higher coefficients of expansion at the higher tempera-
tures. Apparently, the effectiveness of the glass fibers
in restraining the expansion of the resin increases with
increasing temperature.
Soaking in water at elevated temperatures for
several days raised the coefficient of methyl methacrylate
resin by approximately l6 percent on the average. Co-
efficients of the other denture base resins were increased
to a lesser extent by the absorption of water. Table 3
shows the change in coefficient of thermal expansion of
the Lucite specimen as a result of change in water content.
Sufficient data have not been obtained to determine
whether or not the magnitude of the change in coefficient
can be related to the amount of water absorbed. Absorp-
tion of water while the thermal expansion measurements
•
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were being made would produce an apparent increase in the
coefficient of thermal expansion. However, the amount of
water absorbed by the Lucite specimen as shown in Table 3
is too small to account for the Increased change in length
during heating according to data published by Sweeney [4]
which Indicates that absorption of 1 percent by weight
of water results in an increase in linear dimension of
0.23 percent. It is also evident that the increase in
coefficient is considerably greater than would be ex-
pected if the resin specimen and the absorbed water
expanded independently as a mixture of materials. The
average linear coefficient of expansion of water over the
range 20°C to 70°C (68°F to 158°P) is l40 x 10"^ per °C.
[5l. One percent by weight of water in a specimen
of resin with a coefficient of 90 x 10”^ could be expected
to Increase the coefficient of the mixture by approximately
-60.6 X 10 per °C above the expansion of the resin. The
values in Table 3 show that the increase in coefficient
is much greater than this. Water thus appears to increase
the expansion of the resin by some means other than the
thermal expansion of the water.
5. SUMMARY
The coefficient of linear thermal expansion of
methyl methacrylate denture base resins, over the range
nt e£;B9‘tEOnl'' ,vjn9Tsqqa m. mupo'jq t^Luo^t p-ieiv
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al jfit ^6rt;i ^aeblvb" oal£ sJ: dl .-d-nooasq f,P\0
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20°C to 70°C ( 68° - 158 °?) was approximately 86 x 10“^
per °C when conditioned at 50 percent relative humidity.
Coefficients for vinyl-acrylic, epoxy, and styrene resins
were approximately 10, 15 and 25 percent, respectively,
below the value for methyl methacrylate resins.. Glass
fiber-filled methyl methacrylate resins had coefficients
approximately 50 percent below unfilled resins. Absorp-
tion of water caused increased in the thermal expansion
coefficients of methyl methacrylate resins of approxi-
mately 10 to 20 percent and smaller increases in the
coefficients of the other denture base resins.
USCOMM-NBS-DC
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REPERENCES
1. Plastic Properties Chart. Modern Plastic Ency-clopedia. i960 Edition. Plastics Catalogue Corp.,New York, New York. Sept. (1959).
2. Hidnert, P. and Sweeney, W, T. Thermal expansionof magnesium and some of its alloys. BS J. Research1:771 ( 1928 ).
3 . Hldnert, P. Thermal expansion of magnesium andspme of its alloys. BS J, Research 14:523 (1935).
4. Vernonlte Workbench. Vol. 6, No, 3 March (1947).
5 . Smithsonian Physical Tables Ninth Revised Edition.The Smithsonian Institution. Washington, D. C.(1954).
- 12 -*
TABLE 1
MATERIALS
MATERIAL TYPE OP RESIN MANUFACTURER OR DISTRIBUTOR
Acralite-88 Methacrylate Acralite Co . ^ Inc.
Duraf low Methacrylate Product Research Laboratory,,Inc
.
Hydro-Cast Methacrylate Kay-See Dental Mfg. Co.
Vernonlte Gel Methacrylate Vernon-Benshoff Co.
Vernonite P.L. Methacrylate Vernon-benshoff Co.
Tilon Methacrylate Tlconium Dlv . of ConsolidatedMetal Products Corp.
Lucite Methacrylate E.I. duPont deNemours and Co.
Miracle 50 Methacrylate )
l4^ glass filled )
)
American ConsolidatedManufacturing Co.
Mystic 100 Methacrylate )
20-21^ glass filled)
Luxene-44 Vinyl-acrylic Luxene,, Inc.
Jectron Styrene Jectron Co.
Epoxolon Epoxy Surgident,, Ltd,
AVERAGE
COEFFICIENTS
OF
LINEAR
THERMAL
EXPANSION
per
®C
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- 14 -
table 3
EFFECT OF WATER SORPTIONON THE COEFFICIENT OF THERMAL EXPANSION
OF A SPECIMEN OF LUCITE
Conditioningof Specimen
Specimen WeightConditioned
CumulativeWeight Change
Coefficient( 20 -70 °C)
grams X 10-6
In evacuated dessicatorwith- Drierite for 5 mos. 47.322 — —In air during 4 runs 47.328 0.01 89.6
In water at 65 ®Cfor 11 days 47.932 1.29 —
In water during 3 runs 47.947 lo32 105.3
In oven at approximately70 °C for 10 days 47.401 0.17 —
In air during 3 runs ^ 89.0
In air at 23 °C and 50^R.H. for 11 mos.
:
47.416 0.20 —
D!AL INDJCATOR
CIRCULATING WATER BATH
QUARTZ PLUNGER
WATER JACKET —THERMOREGULATOR
1. Fused quartz thermal expansion apparatus and circulating
water bath.
1i
MOLD
FOR
THERMAL
EXPANSION
SPECIMENS
c C c
CO OJ OJCO\ \z
o Q 8
o>1
roCO O ..
zLiJ
2o»
Jo.
o>c oQ <D
_l0)X
c
OLUQ_C/>
00
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x:O'
Figure
2.
Brass
mold
in
which
thermal
expansion
specimens
were
made
.
lO
Oo
yjcrz>h-<a:LJQ.
ijj
h*
H19N3H NJ 39NVH0
Figure
3.
Calculated
thermal
expansion
curves
and
experimental
points
for
three
runs
of
a
Luclte
specimen
after
drying
In
oven
at
70°C
for
10
days
(see
Table
3).
The
curves
have
been
plotted
from
different
Initial
points
to
avoid
overlapping.
CHANGE
IN
LENGTH
Figure 4 . Average thermal expansion curves for all materials in"dry" condition.