Effect of different polishing systems, forces, and durations on surface roughness and phase transformation of monolithic zirconia

Abstract

This study aimed to determine the effect of polishing systems, forces and durations on the surface roughness and phase transformation of zirconia. 72 pieces of fully sintered zirconia size 7 x 5 x 4 mm were fabricated with CAD/CAM, then divided into nine groups depending on the polishing systems and forces. All specimens were ground with fine diamond bur as the control, and initial surface roughness (Ra) was measured. The samples were then polished with one of the zirconia polishing systems (Diazircon or Komet ZR) or porcelain polishing system (Ceramaster), with forces at 1, 2 and 3 newtons. The polishing procedure began with coarse grit polisher for 15 s, twice, followed by fine grit polisher for 15 s, twice. The Ra was measured after each 15 s. X-ray diffraction analysis (XRD) was used to evaluate the phase transformation of zirconia. Repeated measured ANOVA was used to assess the effect of polishing duration on Ra in each group. Two-way ANOVA were used to assess the effect of polishing systems, forces. The results found that increasing duration of polishing significant reducing the Ra (P < 0.001), while higher force also significantly reduced the Ra value (P < 0.001). There was no statistical significance among the polishing systems when polishing with coarse grit polisher (P = 0.376); the polishing systems had a significant effect on Ra when polishing with fine grit polisher (P < 0.001). Komet ZR and Diazircon created a smoother surface than Ceramaster (P < 0.001 and P = 0.002, respectively). Monoclinic phase of zirconia in polishing group varies from 0.62 to 1.18%, which had no significant difference from as-received specimen (0.775%).