Comparative evaluation of dimensional accuracy and tear strength of vinyl siloxanether and polyether impression materials: An in vitro study

Abstract

Aim of the study: The purpose of this in vitro study was to determine the tear strength and dimensional accuracy of vinyl siloxanether and polyether impression material. Materials and methods: According to the ADA specification no. 19, a metal mold was prepared for elastomeric impression materials. A total of 28 specimens were made which were divided equally into 2 groups. The mold was positioned on the block and vinyl siloxanether, and polyether impression materials were syringed into the mold and immediately covered with a polyethylene sheet followed by a flat glass plate. The specimen-forming assembly was placed immediately in a water bath 32°C ± 2°C to simulate the oral temperature and left for double the setting time. When set, the impressions were separated from the test block, and any flash was carefully removed. Evaluation of the dimensional accuracy was made after 24 hours of making an impression. The tear strength test was conducted according to the ASTM 1004 procedure with a 90° angle-shaped specimens free of nicks with a thickness of 1.8 mm. Twenty-eight specimens were made and divided equally into two groups. Vinyl siloxanether and polyether impression materials were manipulated and injected into the mold and immediately covered with a polyethylene sheet followed by a flat glass plate. After setting, the specimens were removed from the mold, and any flash was carefully removed by using a sharp blade. Samples were stretched at a constant rate of 50 cm/minute in the Universal testing machine. The tear strength was calculated using the equation T = F/D kg/cm2 Results: Polyether exhibited less dimensional changes and higher tear strength value than vinyl siloxanether, but there were no statistically significant differences between the two impression materials. Conclusion: Within the limitations of the study, both polyether and vinyl siloxanether exhibited acceptable dimensional accuracy and tear strength. Clinical significance: Although further studies are recommended to evaluate the clinical performance, patient acceptance and cytotoxicity of the vinyl siloxanether as an impression material, results of this study showed that the mechanical properties of the material are comparable to those of polyether, suggesting their clinical success as an impression material during construction of different prosthetic restorations.