Dimensional Accuracy of Polyvinylsiloxane Impressions Models Subjected to Temperature Extremes

Few studies have measured the dimensional stability of Polyvinylsiloxane (PVS) under the extreme temperatures that the material could be exposed to during transit from the dentist to the laboratory, especially if the laboratory is overseas. Objectives: To determine the dimensional stability of PVS when exposed to temperatures as high as +45°C and as low as -17°C. These temperatures were chosen to simulate cargo conditions on airplanes. Methods: A rectangular prism was fabricated out of stainless steel, the (Standard). Thirty custom impression trays made of Triad were fabricated for the standard, ensuring uniform thickness of PVS. These trays were used to take PVS impressions of the standard (light body Extrude PVS). The impressions were randomly divided into three temperature groups (N=10): One group was exposed to +45°C (Hot), another to -17°C (Cold) and the third to +23°C (Ambient) for 10 hrs each, followed by 24 hrs at room temperature to simulate the airplane to lab time. Stone casts were made (WhipMix Microstone). The casts were air-dried for 3 days, then width and length measurements were taken by one “blinded” researcher using an electronic digital micrometer (Mitutoyo IP65). Significance of differences between the treatments was tested using ANOVA and Tukey statistical tests. Results: Significant differences were found between the standard and some of the temperature treatments. (Hot) resulted in largest dimensional changes, and largest mean measurements (10.103 and 45.303mm, width and length respectively), and largest variations (SD .048 and 0.364mm). (Standard) had smallest dimensions, 10.019 and 45.019mm. (Ambient) and (Cold) resulted in similar dimensions, approximately 10.074 and 45.173mm. Differences between the three temperature treatments were not statistically significant. Conclusions: All treatments resulted in larger dimensions than the (Standard). The (Hot) treatment resulted in largest dimensions and variation in dimensions. (Ambient) and (Cold) treatments produced lower dimensional changes as compared to the (Standard).