Effect of different polishing systems on the surface roughness of full-contour zirconia


Background: Adjustment of any premature occlusal contact of any zirconia restoration requires its polishing orglazing in order to restore the smoothness of the restoration. The objective of this in vitro study was to evaluate theeffects of different polishing systems and glazing on the surface roughness of full-contour zirconia.Material and methods: Forty disks (diameter: 8 mm, thickness: 6.4 mm) were prepared from pre-sintered fullcontouredzirconia block; they were colored and sintered in a high-temperature furnace at 1500˚C for 8 hours. Thespecimens were then leveled and finished using grinding and polishing machine and adjusted using diamond disk.The specimens were then randomly divided into four groups (n=10), group I involves samples that were polished using(karat diamond polishing set, Vita zahnfabrik, Germany), group II involves samples that were polished with (zirconiapolishing kit, SMEdent, Shanghai, China), group III involves samples that were polished with (OptraFine® diamondpolishing system, Ivoclar Vivadent, Germany), while group IV involves samples that were glazed using glazingmedium (VITA Akzent Glaze AKZ 25, Vita zahnfabrik, Germany). Surface roughness values (Ra) (in μm) of all thespecimens were recorded at each stage of surface treatment of zirconia disks (leveling and finishing, adjustment ofthe samples and polishing / glazing) using surface roughness tester. Statistical analysis was carried out using one-wayANOVA and LSD tests.Results: The results showed that the glazing group recorded the lowest surface roughness mean value, followed by(OptraFine® polishing system), then (zirconia polishing kit) and finally (karat polishing set) which showed the highestmean of surface roughness. For all groups, there was a statistically very high significant difference of (Ra) valuebefore and after adjustment of the samples. Moreover, there was a statistically very high significant difference in (Ra)value when comparing the adjusted samples with the polished and glazed ones. Karat polishing set group showed astatistically highly significant difference with zirconia polishing kit group (P<0.01). Both, karat polishing set and zirconiapolishing kit groups showed a statistically very highly significant difference (P<0.001) with (OptraFine® polishingsystem) and glazing groups. On the other hand, no statistically significant difference was found between glazing and(OptraFine® polishing system) groups (P>0.05).Conclusions: Adjusting full-contour zirconia with diamond bur or disk resulted in a significant increase in (Ra) thatnecessitates its polishing or glazing to restore the surface smoothness. Furthermore, both glazing and OptraFine®polishing system provided the best surface smoothness, so glazing can be substituted with chairside polishing usingOptraFine® polishing system.