1999 年 18 巻 4 号 p. 430-436
To elucidate the effects of thermal cycling on the viscoelastic properties of four commercial resins for crown and bridge, dynamic shear modulus (G'), mechanical loss tangent (tanδ), Knoop hardness, water sorption and appearance of specimen surfaces before and after thermal cycling test were determined. The changes of G' and tanδ for two materials were insignificant with increased repetitions of thermal cycling. Those of the other two materials were statistically significant: in particular, G' at temperatures above 60°C was inclined to increase slightly and tanδ decreased considerably. While the Knoop hardness of the materials was a little decreased over a number of 75000 thermal cycles, the water sorption almost attained an equilibrium in uptake after 14000 thermal cycles. Furthermore, cracks on the specimen surface were observed after 37500 to 75000 thermal cycles.
From these results, the deterioration of materials was observed as damage to the specimen surface. Moreover, it could be presumed that the materials would be further polymerized during the period of thermal cycling.
