| Part 1 of this study characterized the deterioration of Cerec diamond discs and the subsequent effect on the surface texture and strength of milled Vita Mark II porcelain.; Modulus of rupture for each group was 6.94 (SD = 0.69), 6.59 (SD = 0.59) and 8.18 (SD = 0.59) MPa. No significant differences were found over time between specimens cut with new or used discs. The effect of deep cuts by diamond particles in a fresh disc may off set latent stresses by a dull disc. Exceeding the estimated milling time up to 10% had no effect on Vita Mark II porcelain strength.; Part 2 of this study measured the effect of metallurgical polishing (graded SiC papers plus 0.05 {dollar}mu{dollar}m {dollar}rm Alsb2Osb3){dollar} of the pulpal, cavo- and occlusal surfaces of Vita Mark II porcelain restorations, measured in 3-point fracture.; Modulus of rupture was calculated and tested by ANOVA and Tukey's HSD test: Groups 0-IV broke at 8.0, 9.5, 9.9, 11.2 and 11.0 MPa, respectively. Significant differences (p {dollar}<{dollar} 0.05) existed between groups 0 & 2, 0 & 3, 0 & 4, 1 & 3, and 1 & 4.; Polishing the occlusal surface of Vita II ceramic improves the modulus of rupture 16%. Polishing three to four sides improves strength even more (29 or 27%) over unpolished bars. |
