Thermal dimensional behavior of dental ceramics

The aim of this study was to characterize the relation of dimensional changes of dental ceramic materials as function of temperature. The thermal dimensional behavior of one glass ceramic core, four commercially available veneering porcelains and two experimental veneering porcelain materials was determined on cooling from 450°C to 20°C by means of a vertical differential pushrod thermal dilatometer. The thermal dimensional behavior of the ceramic materials was expressed in three different ways: as linear relation with a linear line fitting procedure; as non-linear relation by a quadratic curve fitting procedure and according to ISO 9693 by a thermal expansion coefficient. For all ceramic materials except the one consisting of aluminum oxide fillers, the thermal dimensional behavior is best described with the polynomial function: Δl/l=C+α1T+α2T2. The description of the thermal expansion coefficient according to the ISO standard on metal is not appropriate for the prediction of a thermal incompatibility of ceramic materials. Except for Vitadur Alpha, the ceramics materials tested showed non-linear expansion; their thermal dimensional behavior can be best described according to the quadratic relation method, second by the linear relation, third as recommended by ISO.