Dimensional Stability of Polyvinylsiloxane Impression Material Subjected to Temperature Extremes

Klooster, Arend, John Palanci, and Warren Wagner

Dentists have been looking for dimensionally accurate impression material that can be utilized in the fabrication of dental prosthetic restorations. Polyvinylsiloxane impression material is advertised as being one of the most dimensionally accurate impression materials. Objectives: The objective of this research was to determine if polyvinylsiloxane (PVS) impression material maintains dimensional accuracy when exposed to temperatures as high as +45 degrees Celsius and as low as -17 degrees Celsius. These temperatures were chosen to simulate temperature extremes to which the impression material may be exposed during transit from dental office to laboratory. Methods: Medium viscosity PVS impression material (Examix by GC America) was applied to a glass slab scribed with hardness indentations for measurement marks along a scribed line separated by 25mm. Twenty seven of these samples were fabricated. Three groups of nine samples each were randomly selected. Nine samples were subjected to +45°C for 10 hours another nine samples were subjected to -17°C for 10 hours and the remaining nine samples were kept at room temperature of+21°C for 10 hours. Samples subjected to heat and cold extremes were returned to room temperature of +21°C for 8 hours and all samples were measured using a Clark Microhardness Tester (Model CM-700) recording three measurements per sample. The readings for each sample were averaged and subjected to ANOVA and Tukey statistical tests. Results: The treatments Hot, Cold and Room resulted in average linear expansions of 44, 44 and 45µm respectively over the 25mm measurement length. The differences between these averages were not statistically significant (p=0.99). The standard deviations for the three treatments were between 15 and 29µm. Conclusion: Subjecting the PVS to -17°C, +21°C and +45°C for 10 hours did not result in statistically significant differences in dimensional change.