Dental Porcelain (Core) with Improved Fracture Toughness and Microhardness

To study the effect of different cooling rates after glaze firing on Radius of radial crack, Fracture toughness and Microhardness of Alumina reinforced porcelain. Total 30 porcelain discs reinforced with aluminium oxide of 8mm diameter×0.6mmthickness were prepared. Specimens were divided into three groups, each group containing ten discs. They were positioned at the entrance of the furnace with a temperature of 593 0 C for ten minutes and then elevated to a non vacuum furnace while the temperature was increased to 970 0 C at a rate of 50 0 C per minute for glaze firing and each group was cooled at a different rate. After cooling, indentations on each disc were made with a Vickers indenter with a microhardness tester loaded with one kilogram for twenty seconds. Statistical analysis revealed significant differences in fracture toughness of porcelain for each of the cooling rates. The slowcooled group had significantly lower fracture toughness than the group with medium cooling rate and the group with rapid cooling rate. Highest fracture toughness value was obtained for rapidly cooled group. The highest VMH value was also obtained for the rapidly