Thermal expansion of layering porcelains for the tetragonal stabilized zirconia

PURPOSE: The purpose of this study was to investigate the coefficients of thermal expansion and shrinkage of an all-ceramic system (cercon) smart ceramics, DeguDent) utilizing tetragonal stabilized zirconia. METHODS: The coefficients of thermal expansion and shrinkage of the core material and the layering porcelains (dentin and enamel) used in this study were measured according to the ISO 9693 standard. Five specimens for the core material and ten specimens for each layering porcelain were tested. The core specimens were milled, sintered, ground and polished. Five of the specimens for each layering porcelain were fired two times, and the remaining five specimens were fired four times. The fired layering porcelain specimens were ground and polished. The coefficients of thermal expansion and shrinkage were evaluated using a push-rod dilatometer at a heating rate of 5 degrees C /min over temperature ranges of 25-700 degrees C for the core, and 25-550 degrees C for the layering porcelain. For each specimen, the coefficients of thermal expansion was determined to be between 25 and 500 degrees C from the plotted curve of expansion versus temperature. RESULTS: For the core material, the coefficients of thermal expansion and shrinkage showed almost the same value (10.8 x 10(-6)/ degrees C). For the layering porcelains, the coefficients of thermal expansion and shrinkage ranged from 9.3-11.1 x 10(-6)/ degrees C. The difference of the coefficients of thermal expansion and shrinkage between the core materials and the layering porcelains was -0.3-1.5 x 10(-6)/ degrees C. The specimens fired two times and the specimens fired four times exhibited almost the same value for each layering porcelain. CONCLUSION: The core material and layering porcelains have a suitable relationship.