Effect of Polishing Wax and Brush on Polishability of Zirconia

Objectives: Full zirconia crowns have been increasingly used due to their excellent esthetics, high strength and chemical stability. However, insufficiently-polished, rough zirconia surfaces tend to cause wear on antagonist teeth. Although mirror-polished zirconia (surface roughness [Ra]=0.17±0.07µm) is reported to decrease enamel antagonist wear significantly, zirconia is not easily polished due to its surface hardness. Polishing waxes are considered to be effective for mirror-polishing of zirconia. This study aimed to elucidate optimal conditions for use of wax in combination with brushes of different hardness for polishing zirconia, and also to evaluate the polishability of zirconia materials of varied translucency using different waxes.
Methods: Zirconia materials of different yttria contents (3Y-TZP, 5Y-PSZ and multi-layers of 3Y-TZP and 5Y-PSZ) were used for preparing specimen discs (Ra=0.4-0.6µm).
Discs were polished with a polishing wax for zirconia (ZG) in combination with Robinson brushes of 3 different hardness levels, and subjected to surface roughness measurement (Ra) and surface gloss measurement (Gs) at 60°. The difference in polishability of zirconia of varied translucency was also evaluated using 3 different waxes (ZG, DPD, RPZ) with SHOFU PIVOT Brush. Data were statistically analyzed (one-way ANOVA, Tukey’s test).
Results: ZG gave higher levels of polishability of zirconia in combination with a softer brush. The difference in translucency of zirconia did not affect its polishability. Polishing performance of waxes was shown as follows: ZG>RPZ>DPD. ZG and RPZ exhibited Ra≤ 0.24µm.
Conclusions: When used with a softer brush, ZG produced smoother and glossier surfaces for all zirconia specimens. The difference in translucency of zirconia did not affect its polishability.
ZG and RPZ gave surface roughness values of zirconia within a range where antagonist wear is not affected. Results suggest that a choice of a polishing wax for zirconia in combination with a soft Robinson brush is recommended for polishing zirconia.