Different polishing methods for zirconia: impact on surface, optical, and mechanical properties

Objectives To test the impact of polishing strategies on zirconia properties. Materials and methods One hundred eight zirconia specimens were divided into nine groups (n = 12/group). Seven groups were polished in the white-stage with either (1) a felt wheel (FW), (2) a felt wheel combined with a polishing paste (FWP), (3) a goat hair brush (GB), (4) a goat hair brush combined with a polishing paste (GBP), (5) a green-state finishing kit (FK), (6) a universal polisher (UP), or (7) with SiC polishing paper (PP), and sintered. Thereafter, the seven groups were divided into two subgroups each and polished using (1) a fine polisher (one-step, n = 6) or (2) a rough and fine polisher (two-steps, n = 6). The positive control group (polish-lab-kit, PLK) was sintered and polished in two-steps. The no polished group (NP) acted as negative control group. Translucency (T%) was measured after white-stage polishing and sintering, and after sintered-stage polishing. Surface free energy (SFE), surface roughness (SR), and flexural strength (FS) were determined. Data were analyzed using one-way ANOVA with Tukey-B post-hoc, t test, and Wilcoxon-test (p < 0.05). Results FWP, GB, FK, UP, and PP presented decreased T% after one-step, while FWP, GB, GBP, FK, and UP presented decreased T% following two-steps polishing. FW showed the highest T% after white-stage, one-, and two-steps polishing. PP presented the lowest SFE. Two-steps polishing resulted in a lower SR for FW, FWP, GB, FK, UP, and PP and increased FS in all groups. Conclusions White-stage polishing improved zirconia properties. Two-steps polishing in the sintered stage, especially when combined with a polishing paste, can decrease SR and increase T% and FS.