Methods: Feldspathic porcelain disks (n=62) (6mm diameter/5mm thickness) were prepared and embedded in epoxy resin. Specimens were polished with 240 grit sandpaper using a polishing-machine, ultrasonically cleaned, rinsed and dried. The surface roughness (Ra) of each sample was measured using a profilometer before polishing to determine the baseline roughness. The samples were then randomly divided into 6 groups (n=10) according to different treatments. Group-1 was polished with diamond paste and the five other groups were polished with the newly developed alumina-zirconia paste with the following ratios of glycerin:alumina powder:zirconia powder by weight: 1:0.5:0.5 (Group-2), 1:0.5:0.75 (Group-3), 1:0.5:1 (Group-4), 1:0.5:1.5 (Group-5) and 1:0.5:2 (Group-6). The specimens were polished for 30 seconds, ultrasonically cleaned, rinsed and dried. Ra-values were determined again. Two specimens from each group and 2 specimens that had not been polished were analyzed using a scanning electron microscope to study the morphology of the porcelain surface. The Ra-value data were statistically analyzed using one-way ANOVA at the 95% confidence level.
Results: The groups of porcelain polished with alumina-zirconia paste at different glycerin:alumina powder:zirconia powder ratios showed different mean Ra-values. These values increased when the weight of zirconia powder in the polishing paste increased. Furthermore, Group-5 showed the lowest mean Ra-value, which was significantly lower than that of Group-1. Surface roughness as observed by SEM showed a correlation with the Ra-value.
Conclusion: The alumina-zirconia paste with a ratio of glycerin:alumina powder:zirconia powder at 1:0.5:1.5 by weight can be used to polish feldspathic porcelain to provide a smooth surface. This polishing paste created a smoother porcelain surface and generated a significantly lower Ra-value compared to diamond paste.