The effect of surface roughness on the Weibull distribution of porcelain strength

The purpose of the present study was to test the hypothesis that glazing will affect the Weibull modulus or the mean flexural strength of dental porcelain. Four groups (n = 30) of specimens were prepared from feldspathic body porcelain (Vita VMK 68). The specimens were tested in groups: original glazed condition (control), and after grinding separately with 1,000-grit, 600-grit, and 100-grit silicon carbide abrasive. A three-point flexure test was undertaken for each specimen. The flexural strength of porcelain and the Weibull modulus were then obtained using a computer program and load-to-failure data. Flexural strength decreased as surface roughness increased, and the differences were significant (p < 0.05), as determined by Tukey's multiple range test, except between the 600-grit group and the 100-grit group. The Weibull modulus of the glazed group was the largest (16.3), and the surface roughness was found to influence the Weibull modulus.