Comparative Evaluation of Wettability at Various Stages of Working Time for Light Body and Medium Body Consistencies of Three Elastomeric Impression Materials.

Aim: The main purpose of this study was to compare the wettability of light and medium body consistencies of three different elastomeric impression materials during their working time. Materials and
Methods: Vinylpolysiloxane, polyether, and vinylsiloxanether light body and medium body impression materials were used to fabricate the test samples. The contact angles of the impression materials were determined at 30th s from the start of mixing until their entire range of working time using a goniometer. The mean contact angles at the early stage of working time and at the end of working time for two consistencies of each impression material were subjected for statistical analysis.
Results: The result showed contact angle of all the impression materials toward the end of working time was less than the early stage with the statistical significance (P < 0.05). The contact angle of the light body impression material was less than the medium body impression materials with statistical significance (P < 0.05) except for vinylsiloxanether impression material.
Conclusion: We have concluded from this study that vinylsiloxanether impression materials exhibited the least contact angle followed by polyether and the highest was recorded for vinylpolysiloxane impression material. Copyright:

INTRODUCTION

An accurate void-free elastomeric impression is influenced by the presence of saliva, blood, and gingival crevicular fluid.[12] Dry field is mandatory for making an impression with these elastomeric impression materials since they are not truly hydrophilic such as hydrocolloid impression material.[34] Achieving an absolute dry field condition during the process of impression making is difficult in most of the clinical scenarios. The formation of voids in the impression is mainly attributed to the presence of moisture.[56] Wettability of unset elastomeric impression material plays a significant role in establishing an intimate contact of material to the oral tissues to obtain a void-free impression.[278]

Vinylpolysiloxane and polyether impression materials are the material of choice for making the final impression because of their excellent dimensional stability and surface detail reproduction.[9] The inherent chemical composition of polyether that contains carbonyl group and ether functional group, interact with water to increase polarity, which makes them hydrophilic.[1011] The polymerized vinylpolysiloxane contains aliphatic hydrocarbon groups surrounding siloxane bonds, making them inherently hydrophobic. To overcome the hydrophobicity, nonionic surfactants have been added to improve the wettability of vinylpolysiloxane. However, these modifications are found to reduce the hydrophobic nature only to lesser extent, which makes them limited to impression pouring with die material.[121314] Vinylpolysiloxanether impression material has been recently introduced to combine the properties of vinylpolysiloxane and polyether by the cross-linking of α,ɷ-divinyl polydimethylsiloxane and α,ɷ-divinyl polyether with organo-hydrogen polysiloxane in the presence of a platinum catalyst.[151617] The property of dimensional stability and deformation recovery of vinylpolysiloxanether is attributed to siloxane groups on the polymer chain, along with the hydrophilic nature of the polyether groups.[18]

Wettability of set elastomeric impression materials has been investigated in the number of previous studies.[192021222324] However, an impression material flows and comes in contact with moist oral tissue only during the working time.[11] During the working time, the wettability of the impression materials is a critical factor that has to be evaluated.

A number of previous studies have investigated the wettability of the vinylpolysiloxane and polyether during their working time, and only a few studies have been reported for the vinylsiloxanether impression material.[1825] The influence of the consistency of the elastomeric impression materials on their wettability during the working time has been investigated only in few studies.[14]

Hence, the present in vitro study was aimed to comparatively evaluate the changes in the wettability of the light body and medium body of three different elastomeric impression materials at various stages of working time.

MATERIALS AND METHODS

Table 1 illustrates the three groups of elastomeric impression materials in two different consistencies used in this study. The materials were manipulated under ambient laboratory conditions (23 ± 1°C and 50% ± 10% relative humidity) in accordance with the manufacturer's recommendations. Distilled water was used as the test liquid. A custom-made mold containing a well of 100 μm depth was fabricated in photopolymer resin using a three-dimensional printer. Using this mold, 10 samples of each impression material were made. Wettability was evaluated by contact angle measurement using a sessile drop method in a goniometer (OCA 20, Data physics instruments, Germany). A water drop (8 μL) was placed on each impression material [Figure 1] at 30th s after the start of mixing. The video capturing of the drop shape was started at the 31st s and continued till the 150th s. The drop shape was analyzed for every second, and the contact angle was calculated [Figure 2].

Table 1

List of impression materials used in this study

Materials	Manufacturer	Consistency	Type	Manufacturer’s working time
Aquasil Ultra LV	Dentsply Caulk	Light body	Vinylpolysiloxane	1’10″
Aquasil Ultra Monophase	Dentsply Caulk	Medium body	Vinylpolysiloxane	1′10″
Impregum soft quick step light body	3M ESPE	Light body	Polyether	1′00″
Impregum soft	3M ESPE	Medium body	Polyether	1′45″
Identium light	Kettenbach GmbH	Light body	Vinylsiloxanether	1′20″
Identium medium	Kettenbach GmbH	Medium body	Vinylsiloxanether	1′20″

Figure 1

Droplet deposition on the specimen

Figure 2

Evaluation of contact angle of impression material

Axisymmetric drop shape analysis profile was used to measure the contact angle using the Software composition analysis software of the goniometer. This is done by fitting the shape of the sessile drop into a theoretical drop profile based on Young-Laplace Equation [Figure 3]. Based on the surface/interfacial tension, the contact angle is determined by the formula:

Figure 3

Young-Laplace equation

Where γsv is the interfacial tension of the solid-vapor, γSL at the solid-liquid, and γLV at the liquid-vapor interfaces.[26]

The mean contact angle of each material was plotted in a graph [Figure 4]. The mean contact angles at the early working time and at the end of working time for each material were tabulated. The data were statistically analyzed using paired “t” test, independent “t” test, and one-way ANOVA, with subsequent Tukey post hoc comparison. The significance was set to P = 0.05. Windows SPSS software (Release 15.01, SPSS Inc., Chicago, IL, USA) was used for all statistical analyses.

Figure 4

Graph

RESULTS

Figure 4 depicts the contact angles determined for the light body and medium body consistencies of impression materials tested. There was the highest contact angle at t = 0 and a steep decline of the curve toward the end of working time in all the materials tested.

In the present study, the mean contact angle of vinylpolysiloxane, polyether, and vinylsiloxanether light body impression materials at the early stage of working time was 109.1°, 71.2°, and 44.8°, respectively, and at the end of working time was 66.2°, 24.5°, and 6.78°, respectively. The mean contact angle of vinylpolysiloxane, polyether, and vinylsiloxanether medium body impression materials at the early stage of working time was 111.7°, 77.6°, and 45.1°, respectively, and at the end of working time was 70.1°, 33.4°, and 6.5°, respectively.

The light body impression materials showed a lesser contact angle than the medium body impression materials at both stages of working time with a statistically significant difference except for vinylsiloxanether. The contact angle of the vinylsiloxanether light body was lesser than the medium body at the early stage of working time without any statistical difference. However, the contact angle of vinylsiloxanether medium body was lesser than the light body impression material at the end of the working time with a statistical significance.

Among the light and medium body consistencies, vinylsiloxanether impression material showed the least contact angle followed by polyether and the highest by vinylpolysiloxane materials both at early stage and at end-stage of working time. There was a statistically significant (P < 0.05) difference for both the consistencies of impression material.

DISCUSSION

The hydrophilic nature of the impression material during setting has attracted increasing interest in recent years. Since the first contact of thin impression material with wet oral hard and soft tissues will have much clinical significance, which is characterized in terms of initial hydrophilicity.[27] Measurements have been taken after the start of impression material mixing to characterize the wetting properties within the respective working times.[112728] Changes in the wetting characteristics of elastomeric impression materials during the working time and curing time were reported by Rupp et al.[28] Once after the placement of liquid drop contact angle decreases with time, and it is most pronounced during the first 2 min of contact as noted by Brukl et al. in their study.[29] In the present study, the wettability during the working time of respective impression material was determined by the contact angles, which were recorded from the time after droplet deposition until the entire range of working time. The contact angle of the impression material at the initial stage at 31st s and at the end of working time for each material was considered for statistical analysis. Since it compares the hydrophilicity of the material from the start of working to the end time, it gives details of the impression. Thus, making it clinically relevant.[25]

In the present study, the mean contact angle at the end of working time was lesser than the mean contact angle at the early stage of working time for all the three light body and medium body impression materials. The decrease in the contact angle at the end of working time for vinylpolysiloxane material could be attributed to the decline in the surface tension of the water due to the dissolution of substrate constituents (surfactants).[14] The decrease in the contact angle at the end of working time for polyether material and vinylsiloxanether is attributed to the presence of polar functional groups in its chemistry.[14] The results obtained in the present study were similar to that of the previous studies for the light body impression materials.[228] However, similar studies evaluating the contact angle of medium body impression materials are lacking in the literature for any comparison.

The light body consistency impression materials had lower contact angles than the medium body consistency at the early and end stage of working time for vinylpolysiloxane and polyether impression materials. This could be attributed to the difference in the filler content of the two viscosities of the impression materials.[30] The contact angle measurements for vinylsiloxanether light body and medium body impression material at the early stage and end of working time were almost similar to each other. Viscosity did not play a significant role in this material as both consistencies exhibited similar consistencies.

Among the three elastomeric impression materials compared, vinylsiloxanether impression materials exhibited the least contact angle followed by polyether and the highest was recorded for vinylpolysiloxane impression material. Surface tension eraser surfactant-tenside I and wetting conditioner surfactant-tenside II present in vinylsiloxanether attributes to its lower contact angle.[18]

The low contact angle of polyether is related to the inherent hydrophilicity of the material, and the apolar chemical structure of vinylpolysiloxane materials attributes to their high contact angles. The results obtained in the present study were in agreement with the previous studies. However, those investigations had not included vinylsiloxanether impression material.

CONCLUSION

From the present study, it can be said that the low contact angle recorded at the end of working time for all the impression materials revealed good wettability while maintaining the flow properties before it undergoes complete polymerization. Although the contact angle of the medium body impression materials was higher than the light body materials, the viscosity of the medium body materials will tend to displace the moisture while recording the surface details. Vinylsiloxanether impression material exhibited the least contact angle among the three impression materials irrespective of the consistencies. Vinylsiloxanether impression material showed the least contact angle, followed by polyether and vinylpolysiloxane. Even then, the contact angle of all the impression materials was <90° at the end of working time ensuring good clinical reproduction of surface details making it clinically acceptable for impression of oral tissues.

The clinical scenarios such as challenges in injecting the material in the gingival sulcus were not simulated. When the material comes in contact with tissue or dentin, occurrence of void or bubble was also not investigated. These may be considered the limitations of the present study. Our study has not evaluated the correlation between the flow properties and the wettability of the impression materials. Hence, further clinical studies are required to verify if these results are reflected by better wetting of the prepared tooth structure under the wet conditions and, in turn, the clinical outcome of the final restoration.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.