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INTRODUCTION
Acrylic pattern resin materials have been widely used in
dentistry for many purposes since their introduction1).
They have been recommended for direct post and core
patterns2,3), intraoral soldering indices for multiple-
unit xed partial dentures4-6), metal frames or clasp
patterns of removable partial dentures7), fabrication of
new crowns to t existing removable partial dentures8,9)
and outer caps of cone telescopic crowns10). Recently,
pattern resins have been used for implant prosthesis
fabrication. Fitting implant restoration passively
without undue stress is required to avoid complications
such as alveolar bone resorption, abutment fracture,
and connecting screw breakage11). These requirements
can be achieved by accurately transferring the intraoral
implant positions to working casts12-15). Impression
copings and laboratory analogs must be splinted rigidly
without positional displacement using pattern resins
through the impression procedures. These pattern
resin materials have several advantages over waxes,
impression compounds, and plaster materials, including
low coefcients of thermal expansion, low tendency for
stress relaxation, and high mechanical strength16). The
exural strength of commercially available pattern
resins [Palavit G (PG; Kulzer, Hamburg, Germany) and
GC pattern resin (GC, Tokyo, Japan)] was reported as
112.8 MPa and 74.5 MPa respectively17). Yamahachi, a
dental manufacturer, provided information about the
self-curing pattern resin Pattern Bright (Yamahachi
Dental, Gamagori, Japan). According to the information
provided, the Vickers hardness value and exural
strength of the resin were 13.4 and 60 MPa, respectively.
Pattern resins are expected to be useful in clinical
dentistry. However, inadequate dimensional stability
caused by polymerization shrinkage has been reported
for various applications of acrylic resins, especially
those involving patterns and indices. Because most of
these pattern resins are based on methyl methacrylate
(MMA), shrinkage occurs during polymerization.
However, almost no reports have been published on
improving the properties of pattern resins. Pattern resin
materials must leave little residual ash after burning.
Therefore, we attempted to produce new acrylic pattern
resins with a low amount of residual ash after burning
and adequate dimensional stability. In addition, we
produced a light-polymerization type resin, which is
easier to operate than a self-polymerization type. In this
study, we selected poly(n-butyl methacrylate) (PnBMA)
or poly(iso-butyl methacrylate) (PiBMA) polymers,
which leave low amounts of ash after burning, as
advertised by their manufacturers. Because it is unclear
which monomers are effective for mixing, we selected
several monomers for use as dental materials: MMA,
ethyl methacrylate (EMA), butyl methacrylate (BMA),
and ethylene glycol dimethacrylate (EGDMA). The
residual ash after burning, Vickers hardness, exural
strength, and volumetric polymerization shrinkage
of each material were evaluated. The data obtained
for the prepared resins were compared with those of a
commercially available pattern resin, PG.
MATERIALS AND METHODS
Materials
Acrylic light-curing resin materials were produced
Physical properties of experimental light-curing pattern resins based on poly
(n-butyl methacrylate) or poly(iso-butyl methacrylate)
Akihiko KADOKAWA1, Sadaaki MURAHARA1, Hiroshi KONO2, Asami UENODAN1, Asako FUCHIDA1,
Fumiko NISHIO1 and Hiroyuki MINAMI1
1 Department of Fixed Prosthetic Dentistry, Kagoshima University Graduate School of Medical and Dental sciences, 8-35-1 Sakuragaoka, Kagoshima
890-8544, Japan
2 Department of Biomaterials Science, Kagoshima University Graduate School of Medical and Dental sciences, 8-35-1 Sakuragaoka, Kagoshima
890-8544, Japan
Corresponding author, Akihiko KADOKAWA; E-mail: hdsthk@yahoo.co.jp
Experimental light-curing pattern resins were fabricated to produce pattern resin materials with adequate dimensional stability.
The light-curing pattern resins consisted of poly(n-butyl methacrylate) or poly(iso-butyl methacrylate) (PiBMA) polymers and
methacrylate monomers. The physical properties, amount of residual ash after burning, Vickers hardness, exural strength, and
volumetric polymerization shrinkage of each material were determined. The data obtained for the prepared resins were compared
with those of a commercially available pattern resin, Palavit G (PG). A lower amount of residual ash was observed for some of the
prepared resins than for PG. The Vickers hardness and exural strength values of all experimental resins were lower than those of
PG. The volumetric polymerization shrinkage of all the experimental resins based on PiBMA was lower than that of PG. These results
suggest that acrylic light-curing resin materials based on PiBMA may be useful for patterning and indexing during soldering.
Keywords: Pattern resin, Residual ash, Vickers hardness, Flexural strength, Polymerization shrinkage
Received Oct 31, 2023: Accepted Mar 13, 2024
doi:10.4012/dmj.2023-278 JOI JST.JSTAGE/dmj/2023-278
This is an open access article under the CC BY license
https://creativecommons.org/licenses/by/4.0/
Dental Materials Journal 2024; : –
Table 1 Materials used in this study
Material Product Manufacturer Code
Methacrylate polymer
Poly(n-butyl methacrylate) M-6003 Negami Chemical, Nomi, Japan PnBMA
Poly(iso-butyl methacrylate) M-0605 Negami Chemical PiBMA
Methacrylate monomer
Methyl methacrylate — Wako Pure Chemical, Osaka, Japan MMA
Ethyl methacrylate — Wako Pure Chemical EMA
Butyl methacrylate — Wako Pure Chemical BMA
Ethylene glycol dimethacrylate — Wako Pure Chemical EGDMA
Pattern resin Palavit G Kulzer, Hamburg, Germany PG
Table 2 Compositions of pattern resin materials used in this study
Polymer Monomer P/L ratio (g/mL) Code
PnBMA MMA 0.9/1 nM
PnBMA EMA 1.2/1 nE
PnBMA BMA 1.4/1 nB
PiBMA MMA 1.9/1 iM
PiBMA EMA 2.4/1 iE
PiBMA BMA 2.7/1 iB
PiBMA EGDMA 2.5/1 iED
PMMA MMA 2.0/1 PG (Palavit G)
using PnBMA or PiBMA polymers and monomers
such as MMA, EMA, BMA, and EGDMA. To light-
cure the materials, camphorquinone (Wako Pure
Chemical, Osaka, Japan) as a photosensitizer and
N-N dimethylamino ethylmethacrylate (Wako Pure
Chemical) as a reducing agent were dissolved in the
monomer to a nal concentration of 1 wt%. Palavit G,
a commercially available self-curing pattern resin, was
selected as the control material. The materials used in
this study are listed in Table 1.
Specimen preparation
The powder-to-liquid (P/L; g/mL) ratios varied from 0.9
to 1.4 for pattern resin materials based on PnBMA and
from 1.9 to 2.7 for those based on PiBMA. The powder-
to-liquid ratio for each combination was determined in
a preliminary trial considering clinically manageable
consistency in order to fabricate specimens whose
deformability was similar to that of a traditional pattern
resin material18,19). However, the wettability between
PnBMA polymer and EGDMA monomer was exceedingly
poor, making it difcult to fabricate the specimen from
these two materials. Therefore, this combination was
excluded from the study. For PG, the P/L ratio was set to
2.0, as described by Morikawa et al.20) and Nakashima21).
The compositions of the resins used in this study are
listed in Table 2. For residual ash, Vickers hardness,
and polymerization shrinkage, the powder and liquid
were hand spatulated for 40 s and packed into a
cylindrical metal mold divided into two pieces. The mold
had an internal diameter of 6 mm and length of 10 mm.
Petroleum jelly was lightly applied to the mold to prevent
the mixture from bonding. The mold was overlled with
the mixture and placed between at glass plates. The
excess mixture was removed using hand pressure and a
cutter knife. The specimens were removed from the mold
in the dough stage. Subsequently, each specimen except
PG was irradiated using a visible light source (α-Light,
Morita, Tokyo, Japan) for 5 min.
For exural strength, the powder and liquid were
hand spatulated for 40 s and packed into a Teon
mold with width, depth, and length of 3, 2, and 35 mm,
respectively22). The top surface of the Teon mold was
covered with a at glass plate. Each specimen except
PG was irradiated using a visible light source for 5 min
(α-Light).
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Fig. 1 Residual ash of each resin material after burning.
Same letters indicate no signicant differences
(p>0.05).
The amount of residual ash after burning
Twenty-four specimens of each resin material were
prepared and divided into eight groups of three
specimens. The three specimens of each group were
stored in a desiccator for one week after polymerization
and weighed using an electronic balance with an accuracy
of 0.01 mg (ER-182A, A&D, Tokyo, Japan) at constant
temperature (23±0.5°C). The specimens were then
burned in a porcelain crucible placed inside a furnace at
700°C for 2 h. The residual ash of each specimen after
burning was weighed at the same constant temperature
(23±0.5°C) and expressed as a proportion of the initial
weight before burning. This experiment was performed
for all eight groups.
Vickers hardness
The bottom surfaces of the cylindrical specimens were
polished using a series of silicon carbide abrasive disks
(P#300, P#600, and P#1200; Sankyo Rikagaku, Tokyo,
Japan). After 24 h of polymerization, Vickers hardness
tests were performed with eight specimens of each resin
material using a microhardness tester (MVK-E, Akashi,
Yokohama, Japan) under a 50 g load for 30 s.
Flexural strength
The top and bottom surfaces of the rectangular specimens
were polished in the same manner as described above.
After 24 h of polymerization, three-point exural
strength tests were performed with eight specimens of
each resin material using a universal testing machine
(TGE-5kN, Minebea, Nagano, Japan) at a crosshead
speed of 0.5 mm/min. The distance between the two
support points was 15.0 mm.
Polymerization shrinkage
The change in the density of each specimen before and
after polymerization was measured using a pycnometer
(TGK, Tokyo, Japan) lled with 5 mL distilled water. The
specimens were immersed in an ethyl alcohol solution
(Ethanol, 99.5%, Wako Pure Chemical) for a few seconds
to prevent air bubbles from attaching to their surface.
The density of each specimen (D) was calculated as
follows:
Ws•S
D=
Ws−(Wa−Wb)
where Ws is weight of the specimen, S is density of the
distilled water at 23°C, Wa is weight of the pycnometer
lled with distilled water and specimen, and Wb is
weight of the pycnometer lled with distilled water
only. The temperature around the sample was kept
constant at 23±0.5°C. The change in the density of each
specimen before and after polymerization was converted
into a volumetric change. The percentage volumetric
polymerization shrinkage (σ) was expressed as a
proportion of the initial volume before polymerization.
This equation can be written as
Vb−Va M/Db−M/Da Db
σ= ×100= ×100=(1− )×100
Vb M/Db Da
where Va is volume of the specimen after polymerization,
Vb is volume of the specimen before polymerization,
M is weight of the specimen, Da is density of the
specimen after polymerization, and Db is density of the
specimen before polymerization. The measurements
before polymerization were performed prior to light
irradiation for the experimental resin materials and
immediately after mixing for PG. The measurement
after polymerization was performed 20 min after light
irradiation of the experimental resin materials and
20 min after the beginning of mixing for PG. Eight
specimens for each resin material were used to study
polymerization shrinkage.
Scanning electron microscopy observation
The three polymers used in this study for pattern
resin materials were sputter-coated with a thin layer
of Au–Pd under vacuum using ion sputter (JFC-
1100E, JOEL, Tokyo, Japan) and observed by scanning
electron microscopy (SEM; JSM-35CF, JEOL) at an
operating voltage of 15 kV. Images were captured at a
200×magnication. The particle sizes and shapes of the
three polymers were examined.
Statistical analysis
A one-way analysis of variance (ANOVA) followed by
Tukey’s multiple comparison test were performed to
analyze signicant differences in the data; a signicance
level of 0.05 was observed. These analyses were
performed using a statistical software (BellCurve, SSRI,
Tokyo, Japan).
RESULTS
Figure 1 shows the residual ash content of each resin
after burning. The amount of residual ash of all the
experimental resin materials did not increase compared
to that of PG, and the decrease was statistically
signicant for nB and iB (p<0.05).
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Fig. 2 Vickers hardness of each resin material after
polymerization.
Same letters indicate no signicant differences
(p>0.05).
Fig. 3 Flexural strength of each resin material after
polymerization.
Same letters indicate no signicant differences
(p>0.05).
Fig. 4 Volumetric polymerization shrinkage of each resin
material.
Same letters indicate no signicant differences
(p>0.05).
Fig. 5 SEM pictures of three polymers used in this
study.
Figure 2 shows the Vickers hardness values of
each resin material after polymerization. Most of the
experimental resins were signicantly less hard than PG
(p<0.05). However, no signicant difference in hardness
value was observed between iM and PG (p>0.05).
Figure 3 shows the exural strength of each resin
after polymerization. The exural strength of each
experimental resin material was signicantly lower
than that of PG (p<0.05).
Figure 4 shows the volumetric polymerization
shrinkage of each resin material, converted from the
variation in density before and after polymerization.
No signicant difference in polymerization shrinkage
was observed between the PnBMA-based resins and
PG. However, compared with PG, all the experimental
PiBMA-based resins underwent less polymerization
shrinkage. The polymerization shrinkage of PiBMA-
based resins was 20%–38% lower than that of PG. In
particular, the value of iB was the lowest among all
materials examined.
The SEM images of the three polymers used in this
study are shown in Fig. 5. The three polymer particles
have a similar spherical shape. The polymer particle
sizes differed considerably. The particle size of PiBMA
was close to 100 μm, which was larger than that of other
two polymers.
DISCUSSION
Pattern resin materials should have physical properties
such as a small amount of residual ash after burning
and some degree of mechanical strength to prevent
deformation or fracture when they are placed or removed
during prosthetic procedures, and low polymerization
shrinkage to produce accurate prostheses.
According to the information provided by the
manufacturer, the PnBMA and PiBMA leave a low
amount of residual ash after burning. Therefore, these
two polymers were selected for this study. None of the
experimental resin materials yielded more residual ash
than PG after burning (Fig. 1). The nB and iB specimens
yielded signicantly less residual ash than PG. Because
the experimental resin materials did not contain
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Dent Mater J 2024; : –
pigments, the amount of residual ash they yielded was
slightly less than that yielded by PG. However, according
to the information provided by the manufacturer, the
inuence of the pigment on the residual ash appeared
to be negligible. Yamahachi, a dental manufacturer,
provided information about the self-curing pattern resin
(Pattern Bright). According to the information provided,
the residual ash content of Pattern Bright at 700°C was
0.067%. Therefore, all the experimental resin materials
can be used from the viewpoint of residual ash.
The hardness values of almost all the experimental
resins were lower than those of PG (18.92) (Fig. 2). There
was no statistically signicant difference in hardness
values between iM and PG. The hardness of PiBMA-
based resins ranged from 13.94 to 16.52. A possible
explanation for this is the difference in their molecular
weights. According to the information provided by the
manufacturer, the molecular weights of PnBMA (290,000)
and PiBMA (260,000) are lower than that of polymethyl
methacrylate (330,000–350,000). Therefore, almost all
the experimental resin materials were less hard than
PG. The exural strength of each experimental resin
material was signicantly lower than that of PG (Fig.
3). The exural strength of PiBMA-based resins were in
the range of 68.4–80.2 MPa. The mechanical strength of
the experimental resins based on PiBMA is presumed to
be equivalent to that of GC pattern resin (74.5 MPa)17)
or Pattern Bright (60 MPa). Danesh et al. reported that
resin materials based on iso-/n-butyl methacrylate could
be used as occlusal splints to withstand masticatory
pressure23). Experimental resins based on PiBMA may
be considered to have acceptable mechanical strengths
for pattern and index materials.
Several methods have been used to determine the
dimensional accuracy and polymerization shrinkage
of acrylic pattern resins. Kusakai measured the linear
polymerization shrinkage of three self-curing pattern
resins [GC pattern resin, PG, and Duralay (Reliance
Dental, Worth, Ill, USA)] poured into a metal mold24). The
linear shrinkage values ranged from 0.67% to 0.83%. He
reported that the shrinkage values were smaller than
predicted because of the existence of residual monomers
and the contact of the specimens with the metal mold.
Harper and Nicholls measured the distortion in several
indexing materials and found that zinc oxide and eugenol
paste produced substantially less mean distortion
than other indexing materials such as pattern resin5).
Although citing that literature, Katoh reported that the
use of pattern resin is popular in clinical practice because
of its easy manipulation6). Nakashima reported that the
main component of PG is MMA, which was measured
using liquid chromatography21). The theoretical
polymerization shrinkage of pure MMA was reported to
be approximately 21% by Mojon et al.18). The P/L ratio of
PG was 2.0; therefore, the total polymerization shrinkage
was approximately 7%. Although PG is based on MMA,
the polymerization shrinkage of 5.93% (Fig. 4) observed
in this study was slightly lower than the predicted
value of 7%. This was probably due to the inuence of
residual monomers and other substances present in PG,
which were not disclosed by the manufacturer. However,
this value is similar to the results of several previous
studies on the dimensional accuracy of pattern resins.
Mojon et al. measured the volumetric polymerization
shrinkage of two self-curing resins (Duralay and PG)
using a dilatometer and linear inductive transducer18).
They found that the mean volumetric shrinkage reached
6.5% for Duralay and 5.5% for PG 17 min after the start
of mixing. They suggested that these resins are not
dimensionally stable and should be used with a method
that compensates for their shrinkage when they are
employed as an index material. Gibbs et al. reported
the volumetric polymerization shrinkage of two self-
curing pattern resins (Duralay and GC pattern resin)
and two light-curing pattern resins [Primopattern LC
Gel (Primotec, Norwalk, CT, USA) and Primopattern
LC Paste (Primotec)]19). The polymerization shrinkage
was determined by measuring the changes in the area
of the specimens using image analysis. The volumetric
shrinkage values were 5.07, 5.72, 5.42, and 7.43% for the
Duralay, GC pattern resin, Primopattern LC Gel, and
Primopattern LC Paste, respectively. The volumetric
shrinkage of the Primopattern LC Paste was signicantly
higher than those of the other three materials. They
reported that a higher polymerization shrinkage might
affect the accuracy of implant prosthesis fabrication.
Danesh et al. used a hydrostatic method to evaluate the
volumetric polymerization shrinkage of self-curing resins
based on MMA (Palapress, Kulzer) and light-curing
resins based on iso-/n-butyl methacrylate (Acrylight,
Schütz Dental, Rosbach, Germany) for occlusal splints23).
They reported a value of 6.1% for Palapress and 6.2% for
Acrylight. No statistically signicant differences were
observed between the two materials.
In this study, volumetric polymerization shrinkage
was calculated from the change in density of each
material before and after polymerization using a
pycnometer (buoyancy method). This method does not
require dedicated shrinkage measuring equipment.
Conventional pycnometer shrinkage measurement
techniques provide a “free” shrinkage value, which means
that the specimens shrink without any hindrance from
the surrounding media19). As shown in Fig. 4, a small
difference was observed between PnBMA-based resins
and PG in terms of polymerization shrinkage. However,
all PiBMA-based resins underwent less polymerization
shrinkage than PG. In particular, the combination
of PiBMA and BMA resulted in a minimal volumetric
polymerization shrinkage (3.70%). As expected, the
combination specimen with a thick P/L ratio exhibited
less volumetric polymerization shrinkage. Although the
experimental resins based on PnBMA with thin P/L ratios
were expected to show large polymerization shrinkage,
measurements were carried out to comprehensively
evaluate the physical properties required for the pattern
resin. As shown in Fig. 5, the three polymer particles
have a similar spherical shape. The polymer particle
sizes differed considerably. The particle size of PiBMA
was approximately 100 μm, which is larger than that of
other polymers. In addition, the particle size distribution
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Dent Mater J 2024; : –
of PnBMA appeared to be considerably dispersed. The
wettability between PiBMA polymer particles and
each monomer may be good because of their small
specic surface areas. Therefore, the powder-to-liquid
ratio increased, and a low volumetric polymerization
shrinkage was observed in the PiBMA-based resins. This
property is clinically favorable for accurate prosthetic
applications.
For future clinical applications, the thermal
expansion behavior and effects on the dental casting
investment of experimental pattern resins during burning
in a furnace should be investigated25). In summary, new
experimental acrylic light-curing pattern resin materials
based on PnBMA or PiBMA were introduced to overcome
the disadvantages of conventional self-curing pattern
and index resins based on MMA. Several polymerization
characteristics were evaluated. Within the limitations
of this study, the experimental resins based on PiBMA,
especially those that combined PiBMA and BMA,
appeared to be suitable as pattern and index materials.
These materials left a low amount of residual ash after
burning and exhibited acceptable mechanical strength.
Furthermore, they exhibited adequate dimensional
stability owing to their low polymerization shrinkage.
CONFLICTS OF INTEREST
The authors declare no conicts of interest.
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