Download Accuracy of Optimized Rubber Base Impression Materials (Linear

Australian Journal of Basic and Applied Sciences, 8(1) January 2014, Pages: 543-551
AENSI Journals
Australian Journal of Basic and Applied Sciences
Journal home page: www.ajbasweb.com
Accuracy of Optimized Rubber Base Impression Materials (Linear and Surface
Analysis)
Lamis Ahmed Hussein
Qassim University, Dental Biomaterials Department, Faculty of Dentistry, Box. 6700. Buraidah. KSA.
ARTICLE INFO
Article history:
Received 21 November 2013
Received in revised form 18
January 2014
Accepted 29 January 2014
Available online 25 February 2014
Keywords:
Impression Material Accuracy,
Geomagic Software,
3D Surface Analysis,
Hydrosystem, Siloxiether,
Polyvinylsiloxane.
ABSTRACT
Background: Accuracy of the impression materials is mandatory for successful
prosthetic outcome. Any dimensional changes in this step transferred to the subsequent
stage of the prosthesis fabrication and lead to impairment of the precision of the cast.
Recently, major enhancement of impression accuracy was developed using hybrid
material (polyether-silicone) and others by incorporating surfactant additives.
Polyether is a well-known hydrophilic material that allow high wetting capability and
superior fine-details reproduction. Thus combined polyether and polyvinylsiloxane
(polysiloxiether) could enhance impression accuracy. In addition the controlled use of
surfactant (hydrosystem) may also optimize impression accuracy. Objective: The
objective of the present study was to assess the accuracy of different optimized rubberbase impression materials using digital linear measurements and 3D surface analysis.
Results: Polyvinyl siloxane showed the highest mean value for both surface deviation
and linear measurements with statistically significant difference at P< 0.05. Poly
siloxiether and hydrosystem showed non-significant difference of both analysis
methods. Conclusion: Within the limitation of current study, the use of the
hydrosystem, specially fabricated for silicone impressions, had a superior surface detail
reproduction of the dental arches and hence a high accuracy. The hybrid components
polysiloxiether had a high capability of surface detail reproduction which could not be
statistically distinguished from hydrosystem results. Polyvinylsiloxane showed less
level of accuracy than the other studied impression materials.
© 2014 AENSI Publisher All rights reserved.
To Cite This Article: Lamis Ahmed Hussein., Accuracy of Optimized Rubber Base Impression Materials (Linear and Surface Analysis).
Aust. J. Basic & Appl. Sci., 8(1): 543-551, 2014
INTRODUCTION
The accuracy of an impression material, considering dimensional stability and details reproduction, is
crucial for creating well-fitted restorations. According to American Dental Association Specification No. 19, an
impression material should be capable of recording details (±20µm) to be acceptable. It is important for an
impression material to reproduce the details of moisture-contaminated dental surfaces accurately. Thus, high
wettability is one of the essential requirements for accurate impression material. (Frank R. et al, 2005; Chong
YH. et al, 1990; Thongthammachat S. et al, 2002)
Impression surface wettability is mandatory to avoid void formation during pouring stone casts.
Researchers used value of contact angle between a substrate, such as stone die surface, and the impression
material as a measure for wettability (Shah S. et al, 2004; Anna SK. Et al, 2009)
Moreover, (Shifra L. et al, 2013) clarified that there are two aspects of wettability should be studied and
distinguished. The first aspect is the ability of the impression material, during setting, to wet the tooth and
mucosal surfaces. The second aspect is the ability of the recorded impression surface to reproduce a detailed
positive replica, typically in gypsum materials. Although there is a correlation between these two aspects, they
are distinct.
Polyvinylsiloxane (PVS) impression material derives its hydrophobicity from its chemical structure. It
contains hydrophobic, aliphatic hydrocarbon groups surrounding the siloxane bond. In contrast, the chemical
structure of the Polyether (PE) enables hydrophilicity by containing carbonyl and ether functional groups. These
functional groups permit water molecules to interact through hydrogen bonding (Norling BK. Et al, 1979; Rupp
F. et al, 2005).
Surfactant was a successful solution in reducing air entrapment during pouring both polysulfide and silicone
impression materials with dental stones. Therefore, (German MJ. Et al, 2008) compared polysulfide treated with
surfactant with a well-known hydrophilic impression material as polyether. The results showed marked
Corresponding Author: Lamis Ahmed Hussein. Qassim University, Dental Biomaterials Department, Faculty of Dentistry,
Box. 6700. Buraidah. KSA.
Phone#:+966533767595, +96663800050;
E-mail:[email protected], [email protected]
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Hussein LA., 2014
Australian Journal of Basic and Applied Sciences, 8(1) January 2014, Pages: 543-551
improvement in the wettability of the modified polysulfide that surpassed polyether. The mechanism by which
the surfactant improved wettability is not clear. There was a hypothesis that the gypsum slurry extracts a small
amount of surfactant from the impression surface resulting in lowering the slurry surface tension. However,
rinsing the impressions for 30 seconds in running water, which may remove surfactant at the surface, did not
reduce the effectiveness of the surfactant additions Vassilakos N. et al, 1993; Lorren RA. Et al, 1976; Blalock
JS. Et al, 2010).
(Shah S. et al, 2004) studied the use of a 3D laser scanner using super-impositional software to assess the
accuracy of impressions. They compared the dimensional accuracy of polyether and polyvinylsiloxane
impression materials using a laser scanner with three-dimensional superimpositional software. The master
model and the casts were digitized with the non-contacting laser scanner to produce a 3D image. The 3D
surface-viewer software superimposed the master model to the stone replica and the difference between the
images was analyzed.
(Anna SK. et al. 2009) conducted study to compare the exactness of simulated clinical impressions and
stone replicas of crown preparations using digitization and virtual three-dimensional analysis. The master dies
and the stone replicaswere digitized in a touch-probe scanner (Procera® Forte; Nobel Biocare AB) and the
impressions in a laser scanner (D250, 3Shape A/S), to create virtual models. The resulting point-clouds from the
digitization of the master dies were used as CAD-Reference-Models (CRM). Discrepancies between the points
in the point clouds and the corresponding CRM were measured by a matching-software (CopyCAD 6.504 SP2;
Delcam Plc). The distribution of the discrepancies was analyzed and depicted on color-difference maps (Lepe X.
et al, 1995; Werner JF. et al, 2008) .
The recent development in the manufacturing of impression material using accuracy enhancement
approaches should be evaluated. Consequently, the objective of the present study was to assess different
impression materials relies on these approaches for their accuracy. The selected materials were studied from
intraoral impressions to validate the actual environment.
MATERIALS AND METHODS
Seven patients were selected randomly (dentulous and partially edentulous having centrals, canines and
second molars). The main exclusion criteria was based on the convenience of the impression making (i.e: no
gagging, limited mouth opening, xerostomia, pain or ulcers). All patients were prepared to undergo alginate
impressions in stock trays. The impressions were poured then the casts were used to prepare acrylic special
trays. The same special tray was used to record the selected arch by the studied impression materials. Four
elastic impression materials were selected; polyether impression material (PE) (Impregum , 3M, ESPE,
Germany),polyvinyl siloxane (PVS) (President, Coltene Whaledent, Switzerland),a newly formulated polyvinyl
siloxanether elastomeric impression material (PVE) (FUS-M, VPS/PE GC Corporation, Tokyo, Japan) and a
topical surfactant, Hydrosystem (HD) (Zhermack, Italy, B& H Technical Services Ltd., Bellevue, Wash. and
Firmadenta, Sudbury, Suffolk, U.K.) used with a modified polydimethylsiloxane wetting agent. The last product
was used in two steps; it was sprayed onto prepared tooth surfaces intraorally before impression making and it
was sprayed on the impression surface before pouring the cast.
After impression making using the studied impression materials, all impressions were poured using hard
stone under vacuum machine to avoid any air bubbles entrapment. Each material appreviation was used for
simplification. Research design included two evaluation methods to differentiate the degree of accuracy of each
impression material.
Fig. 1: Representative of the actual stone models after pouring the impression, a. The virtual 3D model of the
same cast after digitization, b.
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Australian Journal of Basic and Applied Sciences, 8(1) January 2014, Pages: 543-551
Fig. 2: Digital virtual models before and after registrations, a &b, respectively.
A. 3D Deviation Study:
This analyzing tool depended on using reverse engineering software to calculate the 3D mesh deviation
(surface typography) between the reference surface (PE) and the surface of the studied material.
The twenty-eight casts were collected to be 3D-scanned using laser scanner (D-250, 3ShapeA/S,
Copenhagen, Denmark). The twenty-eight 3D models were saved as STL file format then collected and stored in
the computer. The models (virtual and actual) were categorized into four models for each patient, (fig 1. a,b).
The 3D models were imported into Geomagic studio 2012 software (reverse engineering software)
(Raindrop, Research Triangle Park, USA) to be analyzed. The models of each patient were aligned in the XYZ
co-ordinate by the semi-automatic registration process using the 3D model of the (PE) as a reference media and
the other three models as floating ones, (fig.2 a,b).
After registration process, the 3D deviations between studied impression models and the (PE) model were
collected and analyzed (both quantitatively and qualitatively) to interpret areas of difference. The value of the
average mesh deviation of each model was used and the resulted colored map was saved. A customized coloredbar was generated to interpret the areas of changes where green color (in the middle of the bar) denoting 0
changes, red color (on the top of the bar) denoting the highest elevated changes and the blue color represent the
maximum depressed change areas. All data were then statistically analyzed.
B. Digital measurements on the stone casts:
This method depended on selecting certain pre-determined landmarks on the stone models and then
calculating the distances using a precise digital caliber.
Six definite landmarks were selected on a stone model of each patient then duplicated to the other models
(central incisor tooth, canines and second molars, bilaterally). Six distances between landmarks (central-canine,
canine-molar; bilaterally) and (canine-canine and molar-molar) were measured using a digital Vernier caliber
(Capri6-Inch Digital Caliper, Capri tools Co., China) with an absolute accuracy (0.01 mm), (fig. 3). The same
examiner recorded all measurements in two different occasions to con
firm the reliability of the examiner
calibration, with a confidence interval of 95% in two different occasions.
The absolute mean difference of the measured distances between all impression materials and (PE) group
were calculated and statistically analyzed.
The S-Plus Statistical analysis (SPSS) software v13 was used for data analysis. All data were tested for
normality and equality of variance using Shapiro-Wilk and Levene tests respectively. The mesh deviation data
showed normal distribution and so one-way ANOVA test was selected and applied for testing significance at (P
<0.05) followed by LSD test as a post-hoc comparison between groups. On the other hand, the digital linear
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Australian Journal of Basic and Applied Sciences, 8(1) January 2014, Pages: 543-551
measurements were not normally distributed. Consequently, the Kruskal-Wallis test for non-parametric data was
selected for testing significance at (P <0.05) followed by the Mann-Whitney test to perform multiple
comparisons between groups.
Fig. 3: Digital measurement of a pair of landmarks selected using the digital caliper.
Results:
A. 3D Deviation Study:
The mean of the 3D deviation of PVS demonstrated the highest mean and standard deviation values among
all impression materials tested (0.5451± 0.135 mm) with a statistically significant difference at p≤0.05.
The mean of the 3D deviation of PVE (0.3490± 0.104 mm) was higher than HD (0.2539 ± 0.079) with a
statistically non-significant difference at p≤0.05, (table 1 and 2) and (fig. 4).
Table 1: Mean, standard deviation and standard error values of average mesh deviations measured in mm for studied impression materials.
N
Mean
Std. Deviation
Std. Error
95% Confidence Interval for Mean
Lower Bound
Upper Bound
PVS
7
0.5451
0.13586
0.05135
0.4195
0.6708
PVE
7
0.3490
0.10411
0.03935
0.2527
0.4453
HD
7
0.2539
0.07934
0.02999
0.1805
0.3272
Total
21
0.3827
0.16162
0.03527
0.3091
0.4562
Table 2: Comparison between studied impression materials using LSD test.
(I)
(J)
Mean Difference
IMPRESSION
IMPRESSION
(I-J)
PVE
.19614*
HD
.29129*
PVS
-.19614*
PVE
HD
.09514
-.29129*
PVS
HD
PVE
-.09514
* The mean difference is significant at the 0.05 level.
PVS
Std. Error
Sig.
.05822
.05822
.05822
.05822
.05822
.05822
.003
.000
.003
.120
.000
.120
95% Confidence Interval
Upper
Lower
bound
Bound
.3185*
.0738
.4136*
.1690
-.0738*
-.3185
.2175
-.0272
-.1690*
-.4136
.0272
-.2175
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Australian Journal of Basic and Applied Sciences, 8(1) January 2014, Pages: 543-551
Fig. 4: chart showing mean values of average mesh deviations for studied impression materials.
Fig. 5: colored-map showing positive and negative 3D deviations between the control group and the (HD)
group. The right side colored bar showing the selected customized range.
The colored map sample of the 3D deviations of the (HD) group showed minimal positive changes (yellow
to orange colors) seen clearly in the buccal and labial areas of the arch, as well as in the fossae and grooves of
the teeth. In contrast, the negative changes (cyan to blue colors) were seen in the palatal surfaces of the teeth and
soft tissues as well as the cusps and incisal edges of the teeth, (fig. 5).
Fig. 6: colored-map showing positive and negative 3D deviations between the control group and the (PVE)
group.
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Similarly, the colored map sample of the 3D deviations of the (PVE) showed positive changes on the buccal
and labial surfaces of both hard and soft tissues. In addition, buccal slopes of the posterior teeth and palatal
surfaces of the anterior teeth showed also positive changes. In contrast, palatal hard and soft tissues and palatal
slopes of the buccal cusps showed negative 3D deviation changes, (fig.6).
Fig. 7: colored-map showing positive and negative 3D deviations between the control group and the (PVS)
group.
The 3D deviation between the control group and the (PVS) group showed marked areas of negative changes
both in the labial, buccal, and in palatal surfaces ranged from cyan to blue colors. Conversely, little areas of
positive changes were seen in the vertical slopes of the hard palate and sporadically on the occlusal surfaces of
the posterior teeth, (fig. 7).
B- Digital measurements on the stone casts:
PVS showed the highest mean value among all studied materials (0.80 ± 0.27 mm) with a statistically
significant difference at p≤0.05. PVE showed value higher than HD with no significant difference at p≤0.05,
(table 3 and fig. 8).
Table 3: Comparison between studied impression materialsusing Mann-Whitney test.
PVS
PVE
HD
(n=42)
(n=42)
(n=42)
Measurement
Min – Max
0.20 – 1.20
0.10 – 0.60
0.20 – 0.40
Mean ± SD
0.80 ± 0.27
0.34 ± 0.17
0.28 ± 0.09
Median
0.70
0.35
0.30
p1
<0.001*
<0.001*
p2
0.226
χ2: Chi square for Kruskal Wallis test
p1 : p value for Mann Whitney test for comparing between PVS group and each other group
p2 : p value for Mann Whitney test for comparing between PVE group and HD group
*: Statistically significant at p ≤ 0.05
χ2
p
45.414*
<0.001
Fig. 8: Mean values of linear measurements recorded in mm for different studied impression materials.
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Discussion:
Accuracy of the impression materials is mandatory for successful prosthetic outcome. Any dimensional
changes in this step transferred to the subsequent stage of the prosthesis fabrication and lead to impairment of
the precision of the cast. In order to evaluate accuracy of certain impression material, all aspects affecting
material accuracy should be realized (Anusavice KJ, Phillips’, 2003). Optimal accuracy is gained when a
material had proper flow, hydrophilicity, minimal dimensional changes, and chemical stability after setting
(Craig RG, Powers J.M, 2002). Recently, major enhancement of impression accuracy was developed using
hybrid material (polyether-silicone) and others by incorporating surfactant additives.
Whereas standardization of in-vitro laboratory studies were more feasible, clinical studies of impression
materials are difficult to be performed at the same level of standardization (Brosky ME. et al, 2002). On the
other hand, clinical studies are essential to test several impression material properties because they enable
testing materials at the same challenging intra-oral condition. Intra-oral moisture, temperature, and mucosal
texture could change the overall outcome of any impression materials (DeLong R. et al, 2001). Therefore, to
keep such level of standardization during clinical study, twenty-eight impressions were performed using
dispensing device with same special tray for each patient. In addition, single step impression with properly
spaced special tray was selected. The impressions were also poured after the same post-impression time under
vacuum machine.
The scanning laser three-dimensional (3D) digitizer can delineate x, y, and z coordinates from a specimen
without actually contacting the surface. The digitizer automatically tracks coordinates with precision and stores
data as the number of points on a surface (Shah S. et al, 2004). These exacting features suggest that the laser
digitizer might accurately and reliably measure the dimensions of dental impression materials while avoiding
subjective errors. There have been very few studies to this date assessing the accuracy of impression materials
using the laser digitizers. The use of 3D surface mesh deviation was used in the present study as an accurate
analyzing tool that provided not only quantitative measure but also qualitative interpretation. This tool was more
suitable to exchange the several tools of analysis used for the same purpose, as most of these methods were
either not accurate or not suitable for large area with intra-oral configurations (Marković T. et al, 2012;
Schmitter M. et al, 2010; Robinson PB. et al 1996).
The present study compared, using intraoral impressions, three types of materials versus PE impression
material as a reference. PE had an inherent hydrophilicity and unique flow in the oral environment due to its
chemical composition. Conversely, the hydrophobic PVS is the counter model of polyether regarding
hydrophilicity that was later modified to be hydrophilic like the type used in the current study. Moreover, PVE
and HD were modified to improve hydrophilicity. The results of the present study showed statistically
significant difference in both linear measurement study and mesh deviation between PVS and all studied
impressions. This finding coincides with (Shah S. et al, 2004; Enkling N. et al, 2012). They found a similar
level of accuracy between PE and PVE and a statistical difference between PE and PVS. They also confirmed
that there are certain factors that may affect overall impression results such as spacer thickness, impression
techniques, and pouring time. In addition, some authors showed no significant difference between PVS and PE
and they claimed that material handling and technique were the most powerful factor on their studies (GómezPolo M. et al, 2012). Moreover, they clarified that dimensional stability of PVS and PE varied depending on
pouring time. At short pouring times, similar results were recorded, so that both impressions could be used
alternatively. However, this is not the case when pouring was delayed. PVS was found to be more dimensionally
stable than PE in certain circumstances after 7 days (Rodriguez JM. et al, 2011). Similarly, Endo and finger
(Endo T. et al, 2006) clarified that PE impressions show relatively high shrinkage after 1 hour but they
demonstrated acceptable dimensional accuracy after 24 hours if the impressions are not exposed to long-term
relative humidity above about 50%.
One of the most important factor affecting PE wettability and accuracy in dental practice is the type and
time of disinfection process. According to (Shetty S. et al, 2013), the use of 0.05% iodophor as a safe choice of
immersion disinfection for polyether impression material while using 2% glutaraldehyde can be safely
recommended for 10 min of immersion disinfection without affecting the wettability of polyether. In contrast,
5.25% phenol and 0.5% sodium hypochlorite should not be considered for immersion disinfection because it
adversely affects the wettability of polyether materials.
The use of hydrosystem in the present study showed favorable results in both methods of evaluations. This
finding matched the overall results of Robinson PB. et al, 1994; Millar BJ. et al, 1997). They urged clinicians to
use hydrosystem in combination with silicones’ impressions to reduce their surface tension and enhance
wettability. They also added hydrosystem surfactant to reduce the number of surface voids in dies poured from
PVS impressions. They also clarified that hydrosystem was used in earlier studied without controlling its
handling regarding amount, timing, or even type of impression compatible with. They recognized a significant
improvement in the wetting capability when hydrosystem was added to the hydrophobic siloxane impression
material. Although, details about the proper technique used to control that surfactant were not clear. Surfactant
additions were quite successful in increasing the wettability of the addition silicone impression material
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(Anusavice KJ, Phillips’, 2003; Craig RG, Powers J, 2002). (Norling BK. et al1997) found that the
incorporation of certain nonionic surfactants into silicone and polysulfide elastomers increases their wettability
by gypsum products and consequently results in less bubble entrapment in poured casts. They also found that
the beneficial effect of the optimal surfactant is not reduced by rinsing the impression prior to pouring. This was
in agreement with an in-vitro study done by (Robinson PB. et al, 1996), they determined whether the use of a
topical surfactant (Hydrosystem) reduced the number of air bubbles visible on the surface of polyvinyl siloxane
impressions and stone dies. They also concluded that Hydrosystem surfactant reduced the number of air bubbles
on the surface of silicone impressions and stone dies.
Although all types of impression materials were optimized with recent technologies to acquire maximum
accuracy, each material has its unique approach to serve such demand (Schmitter M. et al, 2010). Accuracy of
the HD was developed directly by using independent surfactant compatible with the silicone impression used
while PVE relies on the addition of hydrophilic PE polymer to improve silicone properties. Such modifications
may affect the overall accuracy outcome, which is multifactorial and not only dependent on wettability (Erkut S.
et al, 2005; Wee AG. et al, 2000; Reddy S. et al, 2013). Fortunately, the results of the digital linear analysis
study synchronized with the 3D surface analysis study and confirmed the ranking of the studied impression
materials. In addition, the colored maps of the 3D analysis study clarified different characteristic typography for
each material used. Generally, these typographies showed more similarity between HD and PVE than PVS.
Conlusion:
Within the limitation of current study, the use of the hydrosystem, specially fabricated for silicone
impressions, had a superior surface detail reproduction of the dental arches and hence a high accuracy. The
hybrid components polysiloxiether had a high capability of surface detail reproduction which could not be
statistically distinguished from hydrosystem results. Polyvinylsiloxane showed less level of accuracy than the
other studied impression materials.
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