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Int Chin J Dent 2005; 5: 80-90.

Physical properties and additional characteristics of current
elastomeric impression materials
Guang Hong, DDS, PhD, Hiroshi Murata, DDS, PhD, Ying-Ai Li, DDS, and Taizo
Hamada, DDS, PhD
Department of Prosthetic Dentistry, Graduate School of Biomedical Sciences, Hiroshima University,
Hiroshima, Japan

Purpose: This study evaluated physical properties and additional characteristics of six commercial elastomericimpression materials and effect of a silicone remover on peel bond strengths between impression materials andan acrylic resin tray.
Materials and Methods: Four silicones (Examixfine, Exadenture, Coltex, and President), one polyether(Impregum F) and one polysulfide (Surflex F) were used. One Type 3 (New Plastone) and one Type 4 (NewFujirock) dental stone casts were used. The tests of detail reproduction, compatibility with dental stones,
working time and liner dimensional change were tested by means of International Organization forStandardization (ISO) 4823 and Japanese Industrial Standard (JIS) T6513. The surface roughness (Ra) of dentalstone casts was measured using a profilometer. The peel bond strengths were measured with mechanical testing
device. Statistical analysis was performed using one-way and two-way analysis of variance, StudentNewman-Keuls multiple comparison tests and t-test (α=0.05).
Results: Large differences were not found among the compatibility with dental stone in all type impression
materials (p>0.05). The silicone and polyether impression materials indicated the smallest change between 0
day and 1 day of liner dimensional changes than the polysulfide impression material. The Polysulfide
impression material exhibited longer working time and setting time, and higher bond strength between acrylic
resin trays than the other type of impression materials. When the silicone remover was applied, the values wereapproximately 0 N/mm.
Conclusion: The physical properties and additional characteristics of current impression materials are different
among the material. The silicone remover was useful for removal of polyether and polysulfide impression
materials from an acrylic resin tray as well as that of silicone impression materials.
(Int Chin J Dent 2005; 5: 80-90.)
Key Words: bond strength, detail reproduction, impression material, physical property, surface roughness.

Introduction
Impressions of the teeth and oral soft tissues are frequently obtained during dental treatment.1 Elastomericimpression materials have been used with good clinical results for all kinds of restorations because of theirsuperiority in accuracy, dimensional stability, and reproduction. To obtain well-fitting cast restoration, a highdegree of accuracy should be kept in the impression making. Recently, various elastomeric impression materials
were developed, and widely used. The dimensional change of impression material is the important index which
the timing to pour dental stone to the impressions is decided. Furthermore, the detail reproduction, compatibility
with dental stones, working time, setting time, and elastic recovery after setting of these materials, are importantfor making the dentures and restorations accurately. The impression material must possess sufficient elasticity topermit removal from the mouth without permanent deformation.2 Furthermore, when an elastomeric impression
is removed from the oral cavity, the impression material and the tray must remain attached to each other.
Previously the research concerning setting characteristics,3,4 compatibility with dental stone5-12 anddimensional stability13-15 of impression materials were reported. Relationship between impression materials anda tray material has been also validated by numerous studies.1,16,17 Sometimes dentists fail to take an accurate
impression because of air bubbles and so on. In that case, it is necessary to remove the failed impression
material quickly and completely. Recently the silicone remover for resilient denture liners has been developed.

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There is little information concerning this effect.
The purpose of this study was to evaluate detail reproduction, compatibility with dental stone, liner
dimensional change, working time, setting time and elastic recovery after setting and peel bond strengths to a
tray material of six elastomeric impression materials. In addition, the effect of the silicone remover material onremoval of the impression materials from the tray material was examined.

Materials and Methods
Table 1 gives details of the materials used in this study. Four silicone impression materials, one polyether
impression material, and one polysulfide impression material were used. One Type 3 and one Type 4 dentalstone products were used. The impression material and dental stone were mixed according to the manufacturers’
instructions.
Table 1.

Elastomeric impression materials and dental stone products used.

Material

Type

Batch number

Manufacturer

Examixfine
Exadenture
ColtexPresident
Impregum F
Surflex F

Silicone
Silicone
Silicone
Silicone
Polyether
Polysulfide

009094
10781
JB425
JF049
FW0060620
170881/280881

GC Corp., Tokyo, JapanGC Corp.
Coltene/Whaledent Inc., Mahwah, NJ, USA
Coltene/Whaledent Inc.
Espe, Seefeld, Germany
GC Corp.

New Plastone
New Fujirock

Type 3*
Type 4*01021610404211

GC Corp.
GC Corp.

*The International Organization for Standardization (ISO) specification 6873 (1998).

Detail reproduction test
The detail reproduction of impression materials was examined according to the International Organization forStandardization (ISO) 4823 (2000)18 test method 9.4. Before mixing the impression materials, the test block wascleaned with 99.5% ethanol, and air-dried. The test block and ring mould were stored in the 35±1°C oven for
conditioning for at least 15 minutes.
The mixed impression material was placed on the surface of test block, covered polyethylene film
(50×50×0.035 mm) and pressure applied by the glass plate (50×50×3 mm). After 60 s of the mix, three
specimens were stored to 35±1°C water bath for the minimum time to remove impression from the mouth
recommended by manufacturers’ instructions. Specimens were removed from test ring, and surfaces wereanalyzed using the stereoscopic microscope at ×4 to ×12 magnification under low-angle light. The level of
reproduction of the A-line, B-line and D-line in the impressions was used to assess the detail reproduction.
Compatibility with dental stones
The test for compatibility with dental stone was conducted according to the ISO 4823 (2000)18 test method 9.6.
The impressions of the test block were made in accordance with ISO 4823 (2000)18 test method 9.4.
The dental stone was mechanically mixed with water according to the manufacturers’ instructions’water/powder ratio for 30 s in a vacuum. The dental stone mixture was poured to the slit mould, via mechanicalvibration.

The dental stone/impression material assembly was stored in the laboratory environment(temperature: 23±2°C, relative humidity: 50±10%) for the minimum time to remove cast from the impression

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material recommended by manufacturers’ instructions.
All cast surfaces were examined according to the ISO 4823 (2000)18 to assess the compatibility with dentalstone. On the other hand, the surface roughness of dental stone specimens was measured after store for 1 day atlaboratory environment. The surface roughness was measured by profilometer (Surfcorder SE-3300, Kosaka
Laboratory Ltd., Tokyo, Japan) with a tracing length of 2.5 mm and cut-off value of 0.8 mm.

Fivemeasurements were carried out per material at laboratory environment, and totally 15 points averaged roughness(Ra) per product were calculated.
Liner dimensional change test
The five specimens were made according to the ISO 4823 (2000)18 test method 9.4. The dimensional changes
0 day and 1 day after storage were examined according to the ISO 4823 (2000)18 and the Japanese Industrial
Standard (JIS) T6513 (1991)19 respectively.

The test block line-length and specimens dimensions were

measured by microscope (MM-40, Nikon, Tokyo, Japan) and data processor (DP-202, Nikon) according to the
ISO 4823 (2000)18 test method 9.5 after store for 0 day and 1 day in distilled water at 35±1°C. The liner
dimensional changes (ΔL) after 0 day and 1 day were calculated as follows:
ΔL = 100 [(L1 – L2)/ L1]
where L1 is the distance between lines D1 and D2 on the block, L2 is the distance between lines D1 and D2 on theimpression material specimen at 0 day or 1 day.
Working time, setting time and elastic recovery test
The working time test was examined according to the ISO 4823 (2000)18 test method 9.3. Working time andsetting time of the test materials were determined using a displacement rheometer. Five tests were carried out
for each material both at 23°C (working time) and at 37°C (setting time). The mixed impression material wasplaced between the specimen pedestal and sliding block/perforated test plate assembly of the rheometer. The
sliding block/perforated test plate assembly of displacement rheometer was momentarily displaced 0.25 mm
using finger pressure (1 s at maximum displacement) at intervals of 15 s. The working time was defined as thetime 15 s before corresponding to when initial elastic recovery of the material was observed at 23°C. The setting
time was the time when the elastic recovery reached a final constant value at 37°C (Fig. 1). The elastic recovery
was measured for 10 minutes.

Fig. 1.
Displacement/timegraph for an impression
material tested using
the displacement
rheometer.

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Peel bond strengths test
Ostron II (Powder 260882, Liquid 270192, GC Corp.) was used as a tray material which is a self-polymerizing
acrylic resin. Acrylic tray resin was prepared to 75×25×3 mm according to the manufacturer’s instructions. The
resin plates were smoothed with 240 grit emery papers to remove any adherent adhesive, and were washed withwater for 15 s, allowed to air dry for at least 5 minutes. The test surface of each specimen was coated with theadhesive supplied by the manufacturer and allowed to air dry at room temperature (23±2°C) for 15 minutes.
Every effort was made to confine the adhesive strictly to the prepared area. The mixed impression material wasplaced on the surface of the test blocks, which had been coated with adhesive. Five specimens were prepared foreach material and experiment.
Peel specimens consisted of an acrylic tray resin plate 75×25×3 mm and impression materials 75×25×3 mm
which were bonded over 25 mm of the acrylic specimen and separated over the remaining 50 mm. The
impression materials were set at room temperature (23±2°C) for 20 minutes before testing. The specimens were
set to the universal testing machine (Model 5565; Instron Corp., Canton, MA, USA) and tested in tensile modewith a crosshead speed of 20 mm/minute at room temperature (23±2°C) until complete separation occurred.
The load (N) at which failure occurred was recorded. The peel bond strengths were calculated as follows:
Ps = F W-1 [1 + (1 + E)/2]
where Ps is Peel strength, F applied force, W width of specimen in the peeling area, and E extension ratio ofmaterial (the ratio of stretched to unstretched length).
The modes of debonding were characterized as tear and peel, or snap,20 dependent on whether the debonding
surface was in the impression material only, at the tray resin-impression material interface only, or the
impression material was fracture on the way.
In order to determine the effect of the silicone remover (Siliconeremover, 00642, Tokuyama Dental Corp.,
Tokyo, Japan) on bond strength to a resin tray material, approximately 20 mL of the silicone remover wasapplied between the impression material and resin tray material.
Statistical analysis
All data were analyzed independently by one-way analysis of variance (ANOVA) and two-way ANOVA todetermine whether statistically significant differences existed among the materials. These differences were
tested with the Student-Newman-Keuls multiple comparison tests. In the surface roughness test, dimensionalchange test and bond strength test, the t-test was also conducted to determine the effect of the dental stone type,measuring time and silicone remover, respectively. All data were analyzed at a 0.05 level of significance. Allanalyses were computed with the SPSS for Windows operating system (SPSS 10, SPSS Inc., Chicago, IL, USA).

Results
In the detail reproduction test, all impression materials reproduced 20 µm-line. Table 2 shows the outcome of
the compatibility with dental stone test. In the New Plastone casts, Coltex reproduced 50 µm-line, and theremainder specimens reproduced 20 µm-line. In the New Fujirock casts, Exadenture and President reproduced
50 µm-line, and the remainder specimens reproduced 20 µm-line.
The outcome of the surface roughness test and dimensional change test 0 and 1 day after storage is illustrated
in Figs. 2 and 3. The significant differences were found among the surface roughness of dental stone with madefrom the impression materials (p<0.05). In the New Fujirock casts, President exhibited highest values of surface

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roughness (0.58 µm) among the materials tested. Coltex exhibited lowest values (0.44 µm). No significant
differences were found among the other impression materials (Fig. 2). In the New Plastone casts, Coltex and
Surflex F exhibited lower values (0.39 µm and 0.43 µm), and President, Exadenture, and Examixfine exhibited
higher values than the other materials (Fig. 2). The significant differences were found between two dental stone
products except for Impregum F and President (t-test).
Table 2.

Compatibility with dental stone casts (µm).

Material

Examixfine

Exadenture

ColtexPresident

Impregum F

SurflexNew Plastone
New Fujirock

20
20

20
50

50
20

20
20

20
50

20
20

Fig. 2.
Surface roughness ofdental stone cast fromsix impression materials.
Identical letters indicate
no statistical differences.

Fig. 3.
Liner dimensionalchange ofimpression materials
after 0 day and 1
day. Identical letters
indicate no statisticaldifferences.

The significant differences were found among the liner dimensional change of impression materials at 0 day
and 1 day (p<0.05). The values of liner dimensional change after 0 day ranged from 0.27 % to 0.42 %. No
significant differences were found among Impregum F, Surflex F, Exadenture, Examixfine, and President, andamong Exadenture, Examixfine, President, and Coltex (Fig. 3). President exhibited highest values of liner

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dimensional change after 1 day (0.34 %) among the impression materials. No significant differences were foundbetween Coltex and Impregum F, and between Examixfine and Surflex F. Examixfine and Surflex F exhibited
lower values of liner dimensional changes (-0.35 % and -0.43 %) than the other materials (Fig. 3). From resultsof t-test, the significant differences were found between 0 day and 1 day except Impregum F and President(p<0.05).
The significant differences (p<0.05) were found among the working time and setting time of impression
materials. Surflex F exhibited longest values of working time (183±11 s), and President exhibited shortest
values of working time (90±0 s). No significant differences were found among the Exadenture, Impregum F,
and Coltex (Fig. 4). Fig. 5 shows the outcome of the setting time test. Surflex F exhibited longest values ofsetting time (279±12 s), and President exhibited shortest setting time (105±0 s). No significant differences were
found between the Examixfine and Coltex. All impression materials complied with the ISO standard of detail
reproduction, compatibility with dental stone, liner dimensional change, and working time.

Fig. 4.
Working time of
six impression
materials.
Identical letters
indicate nostatisticaldifferences.

Fig. 5.
Setting time of
six impression
materials.
Identical letters
indicate nostatisticaldifferences.

Fig. 6 shows the elastic recovery of each impression materials. The elastic recovery of all impression
materials increased with the time, and the values of elastic recovery were 100% when setting. The differences85

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were found among the age changes of elastic recovery of each impression materials. Surflex F exhibited slow
setting behavior.

Fig. 6. Elastic recovery of six impression materials.
Table 3 shows the outcome of the peel bond strength test. There were significant differences (p<0.05) among
the peel bond strengths of the elastomeric impression materials to an acrylic resin tray material. The values ofpeel bond strength ranged from 0.012 N/mm to 0.876 N/mm. No significant differences were found between
Impregum F and Exadenture, and among Exadenture, Examixfine, President, and Coltex (Table 3). Surflex F
exhibited the highest values of peel bond strengths (0.876 N/mm) among the materials tested. Impregum F and86

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Exadenture exhibited lower values (0.012 N/mm and 0.160 N/mm) than the other materials. In the case of no
application of the silicone remover, the impression materials exhibited all three kinds of debonding mode.
Table 3.

Mean peel bond strength (N/mm) of impression materials.

Material

Without silicone remover
Mean
S.D.
Category

With silicone remover
Mean
S.D.
Category

Impregum F
Exadenture
Examixfine
President
Coltex
Surflex F

0.012
0.160
0.277
0.299
0.324
0.876

-0.009-0.042-0.010-0.024-0.008-0.020

0.005
0.018
0.119
0.045
0.123
0.154

a
a b
b
b
b
c

0.012
0.042
0.007
0.034
0.003
0.042

d
d
d
d
d
d

S.D., Standard deviation. Category, Identical letters indicate no significant difference between or among materials (p>0.05).

The debonding mode of all impression materials was peel when the silicone remover was applied. Using thesilicone remover produced significantly lower peel bond strength than no application of the remover in all
impression materials (t-test, p<0.01). Significant differences were not found among the peel bond strengths ofthe materials (p=0.526). The values of each impression material were approximately 0 N/mm.

Discussion
The physical properties and additional characteristics of impression materials are important for make a highaccuracy complete denture, crown and fixed partial denture. Adhesive property of impression materials to tray
resin materials is important because this property has an influence the dimensional stability. Therefore in thisstudy, we evaluated physical properties and additional characteristics of six commercial elastomeric impression
materials and effect of a silicone remover on peel bond strengths between impression materials and an acrylic
resin tray.
In the detail reproduction test, all impression materials reproduced 20 µm-line. All impression material/stone
cast combinations reproduced 20 µm-line except Exadenture/New Fujirock, Coltex/New Plastone, andPresident/New Fujirock cast combinations. All impression materials complied with the ISO standard of detail
reproduction. The impression materials used in this study are appropriate for the precision impression clinically.
However, when dental stone is chosen, we should choose an appropriate impression material/stone castcombinations carefully, because the compatibility is different among their combinations.
The significant differences were found among the surface roughness of impression material/dental stone
combinations. Coltex produced smoother surface than the other impression materials. The Type 3 dental stone
casts (New Plastone) from Coltex and Surflex F were significantly smoother than Type 4 dental stone cast (NewFujirock). The Type 4 dental stone casts from Examixfine and Exadenture were significantly smoother thanType 3 dental stone casts. From these results, in the clinic, the Coltex and Surflex F/Type 3 dental stone
combination and the Examixfine and Exadenture/Type 4 dental stone combinations may be appropriate
combinations. For Impregum F and President, both types of dental stone cast may be appropriate.
The differences that the surface of the impressions is hydrophobicity or hydrophilicity would influence thesetting reaction and change the powder/water ratio of dental stone. And it influences the free growth of theneedle crystal of dental stone surface. This may be the reason why difference was admitted in the compatibility

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with dental stones.
The values of dimensional change after 0 day ranged from 0.27 to 0.42%. The tendency of shrinkage wasobserved in all specimens of impressions after 0 day. Most impression materials tended to expand 1 day after
immersion in water probably due to the water absorption. Significant differences were found among thedimensional change between the 0 day and 1 day except Impregum F and President. Large rate of change wasobserved in Examixfine (from 0.33% to -0.35%) and Surflex F (from 0.27% to -0.45%). When these materials
are used in clinic, dental stones must be poured soon after making the impression. Otherwise, the reproducibilityof the impression may be decreased due to the dimensional change of the impression material and the precision
impression may not be making. Small rate of change was observed in Impregum F (from 0.27% to 0.18%) and
President (from 0.35% to 0.34%). The dimensional stability of these materials is stable with time than the othermaterials.

Therefore, there may be a few dimensional changes when these materials are dipped in thedisinfectant solution for a long time.
The advantages of displacement rheometer are as follows: it operation is easy, it requires only a small amountof material, it can detect the onset of elasticity, and it enables the determination of the working time and setting
time of elastomeric impression materials which is based upon readily identifiable and clinically relevant changes
in the elastic properties of the setting material.
Surflex F (polysulfide) exhibited longest values and President (silicone) exhibited the shortest values ofworking time and the setting time. The impression materials having shorter working time, such as President,
must be load into the tray in a relatively short time and inserted it into the oral cavity of a patient. The othermaterials may be margin of the time comparatively. The impression materials such as Surflex F have a longer
setting time. If removed impression from the mouth before impression material does not set completely, it may
influence a dimensional stability of impression. All impression materials exhibited 100% of the elastic recovery
after setting. From this result, these impression materials used in the clinically may be sufficient for the
impression taking of the undercut.
In the bonding tests between the impression material and the tray material, silicone, polyether,
polyvinylsiloxane and polysulfide materials were often used as the impression material.21,22 A self-polymerizing
acrylic resin, light-polymerizing resin and alloy were often used in the tray material.1,2 In this study, weevaluated three types of impression materials, and the self-polymerizing acrylic resin as a tray material. The
thickness of the impression material was adjusted to 3 mm as reported by Grant et al.15 and Payne and Pereira.21
Some studies concerning adhesive properties of impression materials to resin tray materials have been conductedby means of tensile test2,21-23 and shear test.24 However, tensile stress and shear stress are not observed at the
impression materials/tray interface when the elastomeric impression material is removed from the mouth. The
peel testing modality would be thought to simulate clinical behavior more closely when the impression material
is removed from the oral cavity and tray. Thus, peel test was used in this study.
The peel bond strengths between the impression materials and resin tray material ranged from 0.012 to 0.876
N/mm. A significant difference was found among the materials. The chemical compositions of impression
materials would have an influence on peel bond strength between the impression materials and resin tray
material. When silicone remover was applied, the peel bond strengths of all impression materials were near 0
N/mm, and high standard deviations were found on the peel bond strength values. Because peel bond strength
were near 0 N/mm, the influence of the weight of the load cell itself is larger. This may be the cause that the88

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dispersion of peel bond strength values occurred. All three kinds of debonding mode of peel, tear and snap were
found in all specimens when the silicone remover was not applied. However, peel had been found when thesilicone remover was used.
In the clinical situation, the error of the impression is forecasted. The removal of the impression material fromthe tray is important. Moreover, it is necessary to remove the failed impression material from the tray easily inorder to take the impression again efficiently. To remove the silicone impression material from the tray resinand silicone denture liners from the denture base, the silicon removal material has been developed.
One of the main components of the adhesive material for polysulfide impression material is butyl rubber
cement. That for silicone impression material will be poly(dimethyl siloxane) and ethyl silicate. Peel bondstrength of the elastomeric impression materials to an acrylic resin tray material decreased significantly by using
silicone remover because the silicone remover would dissolve the component of these adhesive materials.
In the silicone impression materials, the differences were found among the compatibility with dental stone
except Examixfine, and no differences were found among polyether and polysulfide impression materials.
Polysulfide impression material and Examixfine (silicone) indicated largest expansion tendency of dimensionalchange than other type impression materials. Polysulfide impression material exhibited longer working time andsetting time, higher bond strength and later tendency in setting behavior than other type impression materials.
The results indicated that the dentists must choose the impression materials and combinations of impression
materials/dental stone by the clinical purpose.
When these impression materials are used in the clinic, we should understand physical properties andadditional characteristics of elastomeric impression materials.

Conclusion
The results of this study are summarized as follows.
1. All elastomeric impression materials tested have reproduced the 20 µm-line. No differences were foundamong the compatibility with dental stone except Exadenture, Coltex, and President. Significant differencesin the surface roughness were found among the impression material/dental stone casts combinations.
2. Large differences in the liner dimensional changes after 1 day than 0 day were found among the various
impression materials.
3. Surflex F (polysulfide) exhibited longest working time and setting time. The President (silicone) exhibitedshortest working time and setting time.
4. Significant differences were found among the peel bond strengths between various impression materials andresin tray material.
5. Silicone remover was effective in removal of not only the silicone impression materials but also of thepolyether impression material and polysulfide impression material from the resin tray material.

References
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4. Inoue K, Wilson HJ. Viscoelastic properties of elastomeric impression materials. II. Variation of rheological properties withtime, temperature and mixing proportions. J Oral Rehabil 1978; 5: 261-7.

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Reprint request to:
Dr. Guang Hong
Department of Prosthetic Dentistry, Graduate School of Biomedical Sciences, Hiroshima University
1-2-3 Kasumi, Minami-ku, Hiroshima 734-8553, Japan
FAX: +81-82-257-5684 E-mail: hong@hiroshima-u.ac.jp
Received August 16, 2005. Revised September 22, 2005. Accepted October 20, 2005.
Copyright ©2005 by the Editorial Council of the International Chinese Journal of Dentistry.

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