This study evaluated the effects of impression material type, storage time, and filler proportion on the accuracy of elastometric impression materials. Ten impression materials were tested, including three alginates and five silicones. Impressions were made of metal dies and stone casts were poured at different time periods. Measurements found the addition silicones Aquasil and Exaflex had the greatest accuracy and stability over multiple pourings. The alginate CAVEX showed the least accuracy after 24 hours of storage. When the experimental silicone had a lower filler proportion, it resulted in significantly greater dimensional discrepancy compared to the same material with a higher filler proportion.

1. Factors affecting the accuracy of elastometric
impression materials
S.Y. Chena,
*, W.M. Liangb
, F.N. Chenc
a
School of Dentistry, China Medical University, 91 Hsueh-Shih Road, Taichung, Taiwan, ROC
b
School of Public Health, China Medical University, Taichung, Taiwan, ROC
c
Department of Social Medicine, China Medical University, Taichung, Taiwan, ROC
Received 16 December 2003; received in revised form 12 April 2004; accepted 16 April 2004
KEYWORDS
Impression material;
Accuracy; Storage time;
Filler
Summary Objectives. The purpose of this study was to evaluate the effects of (1)
various impression materials, (2) different storage times and (3) the proportion
of inorganic filler on the accuracy and stability of elastometric impression
materials.
Methods. The impression materials studied included three alginate impression
materials (Algiace Z, CAVEX and Jeltrate), five commercial silicone impression
materials (Aquasil, Exaflex regular type, Express, Coltex fine and Rapid liner) and
two experimental silicone impression materials designed for this study (KE106A
and KE106B). Impressions were made of 10 metal dies that mimicked prepared
crowns. After an impression was taken, dental stone was immediately poured
into the alginate impressions, while the silicone impressions was poured 30 min
later and waited for 1 h for setting. The second and third stone dies were made
1 and 24 h later, respectively. The diameters of the occlusal surfaces of the
metal dies and stone casts were determined using photographs of the surfaces
taken with a Kodak DC 290 digital camera. The pictures were then measured
using a photomicrograph digitized integration system to calculate any discre-
pancy. Because each impression was used to make three rounds of stone dies,
two-factor mixed factorial ANOVA was used to evaluate the effect of materials
and storage time on the accuracy of the stone casts. The simple effects analysis,
combined with multiple comparisons considering the per family type I error rate,
was performed following confirmation that an interaction between the two
factors was significant.
Results. The results showed that: (1) there was a significant interaction
effect between materials and storage times on the accuracy of the impressions.
(2) Two addition type silicone materials, Aquasil and Exaflex, had the greatest
accuracy and stability. (3) The experimental material KE106A had the least
accuracy in the first and second rounds and the alginate impression material
CAVEX had the least accuracy in the third round. (4) The stabilities of CAVEX and
Jeltrate were the least consistent of the 10 materials and decreased significantly
with storage time. (5) When the experimental material had a low proportion of
filler (KE106A), there was a significantly greater dimensional discrepancy
compared to the same material with a higher proportion of filler (KE106B).
0300-5712/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jdent.2004.04.002
Journal of Dentistry (2004) 32, 603–609
www.intl.elsevierhealth.com/journals/jden
*Corresponding author. Tel.: þ886-4-2055674; fax: þ886-4-2014043.
E-mail address: saychen@mail.cmu.edu.tw (S.Y. Chen).

2. Conclusions. The accuracies varied among the 10 impression materials over
three rounds. Of all the materials, the addition type silicone materials, Aquasil
and Exaflex, had relatively greater accuracy and stability. The discrepancy of the
alginate impression materials increased with storage time. The large loading of
filler showed less discrepancy.
q 2004 Elsevier Ltd. All rights reserved.
Introduction
Making impressions to duplicate oral conditions and
tooth morphology is an integral part of prosthetic
dentistry. There are many reports concerning how
to improve the accuracy of impression techniques,
including controlling the room temperature,1,2
using single or double impression techniques,3,4
using individual or custom trays,5,6
etc. Although all
of above factors affect the outcome, the choice of
impression material is possibly the most important
factor.7,8
Clinically, there are many kinds of elastic
impression materials available for dental use.
Generally, they can be divided into two large
groups: (1) synthetic elastomeric impression
materials that include polysulfide, condensation
silicone, addition silicone and polyether. Silicone
impression materials are the most acceptable in
this group.9,10
(2) Hydrocolloid impression
materials. This group includes agar agar and
alginate impression materials, the latter being
more popular. Clinicians are not agreed which of
these two groups is better but, because alginate is
cheaper than impression materials, it is hoped that
it may become the material of choice. In 1989,
Peutzfeldt et al. compared the accuracy of alginate
and elastometric impression materials. They found
one of the alginate impression materials had a
degree of accuracy comparable with other elasto-
metric impression materials.11
In 1990, Craig et al.
compared over 39 types of commercial elasto-
metric impression material and found the addition
type silicone impression material was more stable
than polysulfide, condensation type silicone and
polyether impression materials at 1 day.12
In 1997,
Federic and Caputo compared some of the agar agar
and elastometric impression materials and found
there was no significant difference in the accuracy
of the mould made from the polyether and from two
agar agar impression materials.13
All the above
studies suggested that alginate impression
materials had the potential to replace elastometric
impression materials. In 1988, Lin et al. compared
the accuracy of elastometric impression materials.
They found that polyether was the most accurate,
followed by silicone, polysulfide, alginate and agar
agar.14
At present, elastometric impression
material remains the most popular and accepted
material among dentists. Therefore, comparison of
these two groups of recently developed commercial
products is very important to investigate their
accuracy and stability.
The purpose of this study was to evaluate the
accuracy of impression materials by comparing the
discrepancies between the master dies and stone
casts. Sometimes, in laboratory work, it is necess-
ary to make an accessory cast, so the effect of
different storage times on re-pouring also was
investigated. Inorganic filler is a component of the
non-constricting part of the impression material.
Therefore, we investigated the effect of different
proportions of inorganic filler on the accuracy of
impressions.
Materials and methods
Materials
The impression materials used in this study included
three alginate impression materials: Algiace Z
(Sankin Kogyo KK, Japan), CAVEX (CAVEX, Holland)
and Jeltrate (DENTSPLY ASIA, Hong Kong), five
commercial silicone impression materials: Aquasil
LV (GC America Inc., Chicago, IL, USA), Exaflex
regular type (GC America Inc., Chicago, IL, USA),
Express (3M Dental products, USA), Coltex fine
Coltene/Whaledent Inc., Mahwah, NJ, USA), and
Rapid liner (Coltene/Whaledent Inc., Mahwah, NJ,
USA), and two experimental silicone impression
materials KE106A and KE106B (Shinetu Chemical
Co., Japan). MG Crystal rock (MARUISHI GYPSUM
Co., Ltd, Tokyo, Japan) was the type IV stone used
in this study. Detailed information on the commer-
cial impression materials is listed in Table 1. The
compositions of the experimental materials are
given in Table 2.
Methods
Sample preparation
Ten simulated stainless tooth models were pre-
pared with a diameter of 9 mm, height of 10 mm
S.Y. Chen et al.604

3. and with a bevel to produce an occlusal surface
8 mm in diameter (Fig. 1(A)). Each model was
paired with a metal ring 20 mm in height, 20 mm in
internal diameter and with a puller as the
impression tray (Fig. 1(B)). Both the model and
tray were numbered from 1 to 10 for each
impression test.
Three kinds of alginate impression materials
were used following the manufacturers instructions
for powder/water mixing ratios and working times
to make the impressions. The impression materials
were mixed using an electric mixer (AIGIMAX
AM505, GC Co., Japan) for 10 s, then part of the
material was used to fill a plastic syringe and
injected onto the model, the remainder was put
into the tray and used to make the impression. The
impression materials and metal dies were separated
after 5 min. The stone was mixed by hand in a
powder/water ratio of 10:3 (w/w) within 1 min and
poured as soon as the metal dies and impression
materials were separated. Ten stone casts were
made for each impression material. All the stones
were allowed to set in a plastic storage box. After
1 h the stone casts were separated from the
impressions and the second round stone casts
were made using the same conditions and stored
in the same way. They also were separated 1 h
later. The impression materials were stored in the
box for a further 24 h, then the third round stone
casts were made in the same way.
Five kinds of commercial silicone impression
materials were mixed following the manufacturers
instructions and the impression materials were
separated from the dies 5 min after beginning
mixing. The impressions were put into the storage
box for 30 min to allow the recovery of elastic
deformation. Stone was poured into the
impressions and allowed to set in the storage box
and the second and third round stones were made
using the same conditions as for the alginate
impression materials.
Two experimental silicone impression materials
with different proportions of filler on the sub-
micron (0.02–0.04 mm) colloidal silica (Aerosil R
972) were prepared in this laboratory and used to
evaluate the effect of the inorganic filler. These
two materials included the same amounts of all
components (Table 2), except for Aerosil R 972,
where KE106A had less Aerosil R972 (5 g) than
KE106B (20 g).
Testing methods
The diameters of the occlusal surfaces of metal dies
and stone casts were determined from photographs
of the occlusal surfaces taken with a metal scale
using a Kodak DC 290 digital camera, followed by
measurement using a photomicrography digitized
integration system (Photomicrograph MGDS-260,
Taiwan) on a personal computer. The system used
Table 1 Basic description of impression materials.
Material Types of material Manufacturer Lot No.
Algiace Z Alginate Sankin Kogyo KK, Japan 317011
CAVEX Alginate CAVEX, Holland 991202
Jeltrate Alginate DENTSPLY ASIA, Hong Kong SL319
Aquasil LlV Addition
type silicone
GC America Inc.Chicago, IL,
USA
990831
Exaflex regular
(medium body)
Addition
type silicone
GC America Inc. Chicago, IL,
USA
Base: 052196A;
Catalyst: 052396A
Express Addition
type silicone
3M Dental Products, USA OGLY3D1
Coltex fine (light body) Condensation
type silicone
Coltene/Whaledent Inc., Mahwah,
NJ, USA
Base: FH23;
Catalyst:FE95
Rapid liner (light body) Condensation
type silicone
Coltene/Whaledent Inc., Mahwah,
NJ, USA
FL81
KE106A (light body) Addition
type silicone
Shinetu Chemical Co. Japan Base: 705257;
Catalyst: 706250
KE106B (regular body) Addition
type silicone
Shinetu Chemical Co. Japan Base: 705257;
Catalyst: 706250
Table 2 The composition of the experimental materials,
KE106A and KE106B.
Component (unit: g) KE106A KE106B
Rubber base (KE106) 60 60
Catalyst 15 15
Accelerator 12 12
Aerosil R972 5 20
Talc extra-fine powder 6 6
Pigment 1 1
Accuracy of impression materials 605

4. the Image-Pro Plus version 4.1 software (MEDIA
CYBERNETICS, USA) as image analyzing instrument,
it can trace the margin of the circle of the occlusal
surface automatically and gives the average diam-
eter. The discrepancies between the metal dies and
stone casts were determined by dividing the
absolute value of the differences between the
diameters of the metal dies and stone casts by
the diameter of the metal die and converted into
percentages. Greater values indicate higher
discrepancies.
Statistical analysis
SPSS 10.0 software was used for the statistical
analysis. The two-factor mixed factorial ANOVA was
used to evaluate the effect of materials and storage
times on the accuracy of impressions. The depen-
dent variable was the accuracy of impressions. The
between-impressions factor was the 10 kinds of
impression material (three alginates, five commer-
cial silicones and two experimental silicones) and
the within-impressions factor was storage time at
three levels (30 min, 1 1
2 and 24 h). The simple
effects analysis combined with multiple compari-
sons considering the per family type I error rate was
performed following confirmation that an inter-
action between the two factors was significant.
Following up the significant interaction in the two-
factor mixed factorial ANOVA, the simple effect of
three different storage times for each material was
tested by performing three paired-samples t-tests.
The simple effect of 10 different materials for each
round was tested by performing one-way ANOVAs.
The Bonferroni test was then used to carry out Post
Hoc pairwise comparisons when the ANOVA showed
a significant main effect of the material factor.
The same procedure was used to evaluate the effect
of different proportions of inorganic filler.15
Results
From the results of two-factor mixed factorial
ANOVA, the interaction effect between impression
material and storage time on the accuracy was
affected significantly ðp ¼ 0:001Þ: As such, the
impression material was analyzed separately for
each round of storage time, and the storage time
was analyzed separately for each impression
material. Table 3 and Fig. 2 show the means and
standard deviations of the accuracy of all combi-
nations of 10 impression materials and three
storage times. In addition, the results of simple
tests for the effect of one factor condition on a
specific level of the other factor also are shown.
The results of the effect of material factor were
as follows (Table 3). For the first round ðT1Þ; Aquasil
was the most accurate material [0.70 (0.45%)],
followed by Express [82 (0.64%)] and Exaflex [0.89
(0.66%)], and KE106A was the worst [1.81 (0.77%)].
However, there were no significant differences
among the materials ðp ¼ 0:095Þ: For the second
round ðT2Þ; Rapid liner was the most accurate
material [0.60 (0.42%)] followed by Exaflex [0.78
(0.62%)] and Aquasil [0.98 (0.84%)], and KE106A was
the worst [2.46 (1.69%)]. In this round, only KE106A
was significantly better than CAVEX. For the third
round ðT3Þ; Coltex fine was the most accurate [0.95
(0.53%)] material followed by Aquasil [1.00 (0.79%)]
and Exaflex [1.02 (0.86%)], and CAVEX was the
worst [3.38 (1.36%)]. The results from the third
round showed that CAVEX was significantly less
accurate than all of the other materials, except for
Figure 1 The stainless steel model used for impression. (A) Metal die. (B) Impression tray.
S.Y. Chen et al.606

5. KE106A and Jeltrate, and KE106A was significantly
less accurate than Coltex fine (Table 3).
The results of the effect of storage time for each
material were as follows. For Algiace Z, Aquasil,
Exaflex, Coltex fine and KE106B, there was no
significant effect of storage time. For CAVEX, the
differences in accuracies between time 1 and time 3
and between time 2 and time 3 were significant. For
Jeltrate, Express and KE106A, the accuracies from
time 1 to time 3 were reduced significantly and for
Rapid liner, the accuracy from time 2 to time 3 was
reduced significantly. Overall, the stability of all
alginate impression materials, Algiace Z, CAVEX and
Jeltrate, reduced when the storage times increased
(Table 3 and Fig. 2).
Fig. 3 shows the mean and standard error for the
two experimental materials KE106A and KE106B.
Overall, the accuracy of KE106B is superior to that
of KE106A and KE106B had greater stability than
KE106A. The accuracy of KE106B was significantly
better than that of KE106A in the third round ðp ¼
0:007Þ:
Discussion
An accurate model is indispensable for the fabrica-
tion of a crown or bridge and the choice of
impression material is vital. In 1989, Eriksson et al.
evaluated one agar agar and seven alginates and
two addition silicones.16
They detected the dis-
crepancies in the diameters of the occlusal surfaces
and cervical areas and measured the height of
Table 3 Comparisons of mean and standard deviation of the accuracy in each group ðn ¼ 10Þ based on 10 impression materials and
three storage times.
Materials Storage times Comparisons of storage time effecta
T1 T2 T3 Significant pairsb
Accuracies of impressions (%)
Alg 1.15(0.84)c
1.36(1.20) 1.65(0.96)
Cav 1.09(1.03) 1.30(0.68) 3.38(1.36) T3 . T2; T3 . T1
Jel 1.23(0.75) 1.57(1.01) 2.11(1.18) T3 . T1
Aqu 0.70(0.45) 0.98(0.84) 1.00(0.79)
Exr 0.89(0.66) 0.78(0.62) 1.02(0.86)
Exp 0.82(0.64) 1.26(0.85) 1.35(0.77) T3 . T1
Col 1.03(0.94) 1.33(1.89) 0.95(0.53)
Rap 1.15(0.84) 0.60(0.42) 1.88(1.41) T3 . T2
KEA 1.81(0.77) 2.46(1.69) 2.46(0.95) T3 . T1
KEB 1.52(0.84) 1.78(1.43) 1.36(0.64)
Comparisons of material effecta
(1) F test of 1-way ANOVA p ¼ 0:095 p ¼ 0:041 p , 0:001
(2) Significant pairsb
None KEA . Rap Cav . all except KEA
and Jel; KEA . Col
Alg, Algiace Z; Cav, CAVEX; Jel, Jeltrate; Aqu, Aquasil; Exr, Exaflex; Exp, Express; Col, Coltex fine; Rap, rapid liner; KEA, KE106A;
KEB, KE106B; T1; T2; T3; first round, second and third rounds of experiments.
a
Simple test was evaluated following up the significant effect of interaction between materials and storage times ðp , 0:001Þ from
two-way mixed ANOVA.
b
All results of Post Hoc tests are controlled for family type I error rate ¼ 0.05.
c
Mean (standard deviation), n ¼ 10:
Figure 2 Comparison of accuracy based on materials and storage times. Note: different characters, a and b, represent
significant difference within each material.
Accuracy of impression materials 607

6. the stone and stainless steel model. They found
that the occlusal surface of the stone cast was
smaller than that of the master die, and that the
height of the stone cast was less than that of the
master die. In addition, the cervical portion was
larger than that of the master die. This showed that
the constriction area of the impression material
varied in different parts of the stone cast. This
phenomenon is complicated and difficult to explain.
In order to simplify the comparison in this study, we
measured only the diameters of metal dies and
stone casts. Some of the stone casts had small
bubbles or obscure areas on the outer margin of the
occlusal surface, so we measured only the inner
diameters of the occlusal surfaces.
The discrepancies between the stone dies and
metal casts had positive and negative values, which
also was reported by Eriksson et al.16
In order to
avoid false results due to the positive and negative
values canceling each other out, the data were
converted to absolute values and the accuracies
were calculated in percentages. The smaller values
of the percentages indicate greater accuracy.
Because the mechanical properties of the stone
material are influenced predominantly by the
water/powder ratio,17
all the specimens in this
study were made using the ratio 10:3 (w/w).
Our results showed that, in the first and second
rounds, the alginate impression materials had
accuracies close to those of the elastomeric
impression materials. However, after 24 h, the
alginate impression materials were relatively
unstable compared to the elastomeric impression
materials. In addition, under magnified conditions,
some of the stone cast surfaces which were made
using alginate impression materials were rougher
than those made using rubber elastomeric
impression materials. This may be caused by the
inhibitory properties of hydrocolloid materials in
the plaster setting reaction. Therefore, the algi-
nate impression materials may have the same
degrees of accuracy as those of elastomeric
impression materials but, in reality, alginate
impression materials still perform more poorly
than rubber base impression materials. In 1989,
Peutzfeldt and Amusen studied the accuracies of
alginate and elastometric impression materials.
They found that one kind of alginate impression
material was as good as the elastometric impression
materials.12
In 1997, Federic and Caputo compared
the accuracies of two agar agar and three elasto-
metric impression materials. They also reported
that the accuracies of agar agar were the same as
polyether impression materials. Alginate
impression materials appeared to have accuracies
as good as those of the elastometric impression
materials.13
However, if water loss and the for-
mation of surface roughness are considered, the
properties of elastometric impression materials
may be better than alginate impression materials.
Johnson and Craig compared the accuracy of four
types of elastometric impression materials with
different storage times, and found no significant
effect of storage time for the addition silicone
impression material.18
Our results were not con-
sistent with their findings. Two of the five silicone
impression materials had a storage time effect,
including Express and Rapid, but the accuracy for
each storage time was still good compared to the
alginate impression materials (Table 3).
The alginate impression materials have evapor-
ation properties. If they are not placed in a tightly
closed storage box, the impression materials con-
strict considerably and lose their elasticity.19
This
not only causes large discrepancies but also makes
it difficult to separate the model. Therefore, we
stored alginate impression materials under con-
ditions of 100% relative humidity.
The accuracy of the elastometric impression
materials was relatively stable among different
storage times and their discrepancies were caused
predominantly by the reaction of the com-
ponents.20
However, the components of commer-
cial products were usually difficult to investigate,
hence two kinds of experimental elastometric
impression materials were prepared in this labora-
tory and used to evaluate the effect of the inorganic
filler. In this study, the sub-micron (0.02–0.04 mm)
colloidal silica (Aerosil R 972) was used, because it
provides increased volume with relatively little
weight. The data revealed that when the proportion
of the filler increased, the accuracy increased. In
1992, Fano et al. studied the dimensional stability
of silicone impression materials. They reported that
the higher the viscosity, the less the constriction.8
In 1988, Mandikos reported that lower viscosity
materials showed the greatest changes due to their
Figure 3 Comparison of accuracy of KE106A and
KE106B. Note: time 1: p ¼ 0:422; time 2: p ¼ 0:351;
time 3: p ¼ 0:007; based on two-sample t-test for
comparisons of the two materials.
S.Y. Chen et al.608

7. lower filler content.20
The results of this study
agree with those reports.
A larger volume of filler causes less elasticity and
fluidity, which results in lower accuracy, so further
studies are needed to determine the optimum
proportion of inorganic filler and methodology. In
1992, Hung et al. compared the accuracy of a one-
step versus two-step putty wash addition silicone
impression technique and found that the one-step
impression technique was more accurate than the
two-step impression technique.3
In the same year,
Chee and Donovan reported that the simultaneous
putty-wash impression technique is the worst
method.21
In 1995, Lee et al. compared the one-
step with the two-step impression technique under
conditions of minor movement, and no significant
differences in accuracy were observed.22
In our
study, we investigated the effect of different ratios
of inorganic filler on accuracy, but we did not
attempt to compare one-step and two-step
methods, although this may be the subject of
further research.
Conclusion
In conclusion, the two-factor mixed factorial
ANOVA showed that the accuracy in three rounds
varied among the 10 impression materials ðp ,
0:001Þ: Two addition type silicone materials, Aquasil
and Exaflex, had the greatest accuracy and stab-
ility. Two alginate impression materials, CAVEX and
Jeltrate had the least stability and the accuracy
decreased significantly when the storage times
increased. It seems that higher filler component
may increase the accuracy.
Acknowledgements
We are indebted to Dr Tim J. Harrison of the Royal
Free and University College Medical School of
University College London (London, United King-
dom) for critically reading the manuscript.
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