The first and most important part of prosthetic restoration stages is to obtain negative model of jaws with an impression material. Impression materials used in restorative dentistry are traditionally divided into two groups of elastic and inelastic ones; elastic impression materials are divided into two groups as hydrocolloids and elastomers (1).Agar-agar and alginate impression materials are in group of hydrocolloids while polysulfide, polyether, condensation silicone, and vinyl polysiloxane (VPS) impression materials are in elastomeric group of impression materials (2). Compared to other impression materials, VPSs have advantages such as recording details, dimensional stability, polymerization contraction and no by-products released (3). However, despite their favorable properties, low wettability is considered a disadvantage in clinical use for VPS impression materials (4-6). Polymerization reaction between silane and vinyl groups produces a cross-linked silicon rubber in VPS impression material (7, 8). Siloxane bonds surrounded by aliphatic hydrocarbons in silicone rubber give material hydrophobicity property (9).Thus, low surface energy of silicone-based impression materials reduces their wettability (10). This situation prevents formation of a suitable and non-porous plaster model. Saliva and oral fluids contaminated dental impressions can cause cross-infection (11-13). Growth of microorganisms is observed in 77% of the impressions washed only under water (14). Therefore, impressions should be disinfected after removal from oral cavity and before pouring the plaster model (11, 12, 15). Disinfection goal is to remove microorganisms without causing any surface changes in the impression (16). Disinfection of impressions must be performed in clinics and laboratories. Disinfection process is performed by spraying or immersion methods. The immersion disinfection method ensures that all surfaces of dental impressions are exposed to disinfectant. Spraying and immersion disinfection methods using antimicrobial agents during mixing of plasters could affect several mechanical properties, including application time and dimensional stability in impressions and models (17). For disinfection of impressions, agents such as glutaraldehyde, iodophor, sodium hypochlorite, ethyl alcohol, isopropyl alcohol, benzalkonium chloride, and chlorhexidine are used (18). The term “wetting” can simply be named as a coating of a surface by a liquid (19). However, wetting may be defined physically as the contact angle formed between a liquid drop in thermal equilibrium and a horizontal surface (20). Depending on the surface type and liquid type, droplet can be of various shapes (21). Specifically, the "contact or wetting angle" is the angle formed at the interface between the droplet and the horizontal surface (21). In general, smaller contact angle indicates good wettability, and greater contact angle indicates poor wettability (7, 22). Hydrophilicity, which is the measure of the liquid's capability of dispersing onto a surface, can be quantitatively analyzed by using dynamic contact angle analysis (23, 24). This video-based drop shape analysis system can easily capture and measure contact angles, which change from initial contact, by analyzing a series of high-resolution sessile drop images (23, 24). To determine the hydrophilicity of impression materials, contact angle measurement between distilled water drop and flat surface of the material is a conventional method (25). This study aims to evaluate surface wettability of additional silicone impression materials, which are immersed in different disinfecting agents for different periods of time. The first hypothesis of the study is that wettability of specimens will vary according to impression materials, type of disinfectants and disinfection times, and the second hypothesis is that wettability of impression materials will decrease as the residence time in the disinfectant increases.

Materials and Methods

For this study 90 disk-shaped specimens 15 mm in diameter and 5 mm in height were prepared. Five different impression materials were used and 18 specimens were assigned to each one. Four of the used impression materials were selected to be of vinyl polysiloxane (VPS) formula, 1 of them was selected to be of vinyl polyether siloxane (VPES) formula and heavy body form. Molds with similar sized slots were used as specimens which allowed making at least ten specimens at the same time. The mold was placed on a clean and flat surface to ensure smoothness of the mold specimen surfaces. Then cartridge of the impression material was placed in silicone mixing device (Pentamix 2; 3M ESPE, Seefeld, Germany) and the device was operated. Homogeneously mixed impression materials were applied inwards of these slots.  After the cavity structures were filled, a glass slab was placed in a way that it came on top of the impression materials and the same researcher applied equal force to each impression material specimen. Following hardening of the impression materials, specimens were carefully removed from the slots. The specimens obtained from each impression material were randomly divided into six groups with three specimens in each group according to disinfectant type and disinfection time. Two different alcohol-based impression disinfectants that are commonly used in our clinic were selected in this study. Disinfection was performed by immersion method, and time period of specimens immersed in disinfectant was determined to be 1 minute, 1 hour, and 24 hours. Table I provides information on impression materials and disinfectants used in this study. After disinfection process, specimen surfaces were washed under running water and dried thoroughly, and were subjected to surface wettability (contact angle) testing by same researcher in the Attention Thea Flex (Biolin Scientific AB, Vastra Frölunda, Sweden) device. A drop of distilled water was dropped on specimen surface while impressions were at the focal point of camera. It was in a range of 0-10 seconds, at 24 °C for each specimen. Dispersion of water was observed by a camera, and a 10-second video was recorded. The contact angle values for each specimen were obtained from right, left, and middle regions, and for one specimen, a total of 140 measurements were obtained in the range of 0-10 seconds separately for each angle. By taking the average of these measurements, mean contact angle value of each specimen in the 0-10 s range was obtained, and images were saved.  The data were evaluated in ANOVA test according to 5x2x3 factorial arrangement to test the statistical differences among group means in the SPSS 20.0 statistics package software (IBM Corp. Released 2011. IBM SPSS Statistics for Windows, Version 20.0. Armonk, NY: IBM Corp.). Duncan’s multiple range test was used to separate means, and differences were considered statistically significant at P<0.05.

Table I. The impression materials and disinfection agents used in the study

 Results

After analyzing results, it was observed that there was a statistically significant difference in interactions of impression material-disinfectant-disinfection time (P<0.05). There was a significant difference between the disinfection times (P=0.001), however there was no statistically significant difference between impression materials and disinfectants (P>0.05) (Table II). According to results of Duncan’s multiple comparison test, a statistically significant difference was determined between disinfection time of 1 minute and disinfection times of 1 hour and 24 hours. Smaller contact angle values were achieved with disinfection for 1 minute.

As a result of the two-factor treatment means for the disinfectants; Cavex Impresafe showed statistically significant difference (P<0.01), but Zeta 7 Spray did not show statistically significant difference in interactions of impression materials - disinfection times (P>0.05). As a result of two-factor treatment means for the disinfection times; disinfection of 1 minute showed statistically significant difference (P<0.05), the other disinfection times did not show statistically significant differences (P>0.05) in interactions of impression materials - disinfectants. The lowest contact angle value was seen in the EXA’lence specimen immersed in Zeta 7 Spray for 1 minute (100.66±11.66), while the highest contact angle value was seen in the V-Posil specimen immersed in Cavex Impresafe for 24 hours (120.57±0.89). The least squares means, standard deviations, and in-group comparisons of each materials were presented in Table III, and the contact angle images were demonstrated in Figure 1 and 2. The plots of interactions of groups are presented in Figure 3 and 4.

Table II. Variance analysis table and Interactions of contact angle values of the groups

Table III. Least Squares Means and Standard deviations for Disinfectants, Impression Materials and Disinfection Times.

Means in column/row with different superscripts are significantly different at P

Fig. 1. The CA images of impression materials that have been left in Zeta 7 Spray for 1 minute.

Fig. 2. The CA images of impression materials that have been left in Cavex Impresafe for 1 minute.

Fig. 3.  Plots showing contact angle changes depending on time of impression materials immersed in Zeta 7 Spray.

Fig. 4. Plots showing contact angle changes depending on time of impression materials immersed in Cavex Impresafe.