Purpose: Because of existing controversy, the present study investigated 3 methods for reducing surface roughness and improving the strength of porcelain restorations.
Materials and methods: Ninety laminated In-Ceram/Vitadur Alpha self-glazed porcelain disks were fabricated and randomly divided into 3 groups (n = 30 each). Group 1 consisted of 30 of the original disks. The remaining 60 disks were then polished by 6 operators according to the recommendations of the American Academy of Esthetic Dentistry; group 2 consisted of 30 of these polished disks. The remaining 30 polished disks were reglazed (group 3). Average roughness values (Ra) of the veneers were measured by a profilometer. In each group, 20 disks were subjected to a flexure test, with 10 of the In-Ceram cores and 10 of the Vitadur Alpha veneers placed in tension.
Results: The Ra values were 0.5 +/- 0.1 micron, 0.7 +/- 0.3 micron, and 0.4 +/- 0.1 micron for groups 1 to 3, respectively. Following one-way analysis of variance (ANOVA), Bonferroni's multiple comparison tests found that groups 1 and 3 were significantly smoother than the polished group (P < 0.001). Reglazed disks were also significantly smoother than the original self-glazed disks (P < 0.01). With the veneers in tension, the flexural strengths were 151 +/- 22 MPa, 118 +/- 22 MPa, and 172 +/- 27 MPa for group 1 to 3, respectively. Following one-way ANOVA, Bonferroni's multiple comparison tests found that groups 1 and 3 were similar and were significantly stronger than the polished samples (P < 0.05 and P < 0.001).
Conclusion: Reglazing polished porcelain surfaces significantly improved the surface texture and flexural strength of the materials tested.