Abstract
Statistical fatigue life for body dental porcelains, cooled in a furnace and in air, was predicted from measurements of post-indentation slow growth of radial cracks in water and in air. Cracks were induced in the surfaces of porcelain discs by a Vickers indenter at an applied load of 9.8N. Crack lengths were measured at various times over a period of 5 months to calculate the stress corrosion susceptibility coefficient, n. Lifetime under service stress was estimated from the measured value of n. The ratios of service stress to fracture strength were calculated as 0.47 and 0.69, respectively, for glassy and feldspathic porcelains which were cooled in a furnace and aged in water. The corresponding ratios for tempered (cooled in air) specimens were 0.58 and 0.67, respectively. These were estimated values when service life exceeds 10 years. The results suggest that the air cooling process can effectively increase the service life of glassy porcelains, but, for feldspathic porcelain it is less effective.
