Evaluation of surface treatments of monolithic zirconia in different sintering stages

Purpose: This study evaluated the effect of surface treatment of zirconia in pre-sintered and post-sintered stages on its surface roughness, phase transformation, and biaxial flexural strength (BFS).

Methods: Zirconia ceramic discs (n=40) having a final dimensions of 12mm diameter and 1.2mm thickness were milled then divided into three main groups according to the type of surface treatment performed (Group 1 (n=16); air-abrasion using Al₂O₃ particles, Group 2 (n=16); silica coating using Rocatec soft, and Group 3 (n=8); a control group receiving no surface treatment). Groups 1 and 2 were divided into two subgroups each according to the stage in which the surface treatment was performed (Subgroup A; surface treatment performed in the pre-sintered stage and subgroup B; surface treatment performed in the post-sintered stage). Surface roughness, phase transformation, and biaxial flexural strength (BFS) were later assessed. Data was then analyzed using two-way ANOVA and Tukey post-hoc tests at a significance level of p≤0.05.

Results: Subgroups treated in the pre-sintered stage showed higher mean Ra in μm (1.81±0.36) when compared to the subgroups treated in the post-sintered (0.68±0.07) stage and the control group (0.51±0.10) (p≤0.05). The pre-sintered treated group and the control showed no monoclinic phase while the post-sintered group showed significantly higher portions of monoclinic phase. Regarding BFS the post-sintered treated group had statistically significant higher values in MPa (1228±81) when compared to the pre-sintered treated group (940±101) and the control (1019±82) (p≤0.05).

Conclusions: Air abrasion in the pre-sintered stage might be a promising surface treatment method to produce promising surface roughness values of zirconia without subjecting it to early degradation.