The influence of multiple firing on thermal contraction of ceramic materials used for the fabrication of layered all-ceramic dental restorations

Objectives During the production of layered all-ceramic restorations transient and/or residual thermal stresses may be formed which may affect a restorationʹs longevity. The aim of this study was to evaluate the influence of multiple firings on the thermal behavior of veneering porcelains and a ceramic core. Methods The materials tested were: Empress 2 Core, Empress 2 Veneer and Eris glass–ceramics, Carrara Vincent and an experimental leucite-based veneering porcelain, Vitadur-Alpha aluminous porcelain, and two porcelains designed for titanium (i.e. Duceratin Dentine and Enamel). The thermal contraction coefficient of the materials was measured by means of dilatometery. The thermal contraction coefficient was measured during cooling and calculated over the temperature range of 450–20 °C by linear regression. One and two-way analysis of variance together with Tukey post-hoc tests were used as statistical analysis. Results Repeated firing affects the thermal contraction coefficients of Empress 2 Veneer, Carrara Vincent porcelain and the experimental porcelain. The thermal contraction coefficients of Empress 2 Core were significantly different from Vitadur-Alpha, Carrara Vincent, experimental porcelain, and Duceratin porcelains. The contraction coefficients of Empress 2 Veneer and Eris were closest to that of Empress 2 Core. Significance The Empress 2 Core and Eris glass–ceramics, the aluminous porcelain and Duceratin porcelains showed better thermal stability after repeated firing than leucite porcelains. It can be concluded that due to the thermal stability of glass–ceramic materials, layered all-ceramic restorations of these materials may perform better.