Effects Of Grinding And Polishing On Surface Characteristics Of The Zirconia Fabricated By 2 Manufacturing Processes:wet Deposition And Dry Milling

Objective:Through in vitro experiments,the grinding efficiency of monolithic zirconia fabricated by two different manufacturing processes ground by the standard-grit diamond bur and the extra fine-grit diamond bur was preliminarily evaluated,as well as the polishing effect of the polishing kit and the polishing brush.The optimal grinding and polishing solution was formulated according to the results.Then the optimal solution was used to evaluate the effects of grinding and polishing on surface characteristics of the 2 different monolithic zirconia.Methods:Part I:Two types of monolithic zirconia specimens,wet deposited zirconia and dry milled zirconia,were fabricated by wet deposition and dry milling,respectively.The specimens of each zirconia type were randomly assigned into 6 groups(n=10):as-sintered,ground by the standard-grit diamond bur,ground by the standard-grit diamond bur following polishing by the polishing kit,ground by the standard-grit diamond bur following polishing by the polishing brush,ground by the extra fine-grit diamond bur,ground by the extra fine-grit diamond bur following polishing by the polishing kit,ground by the extra fine-grit diamond bur following polishing by the polishing brush.The grinding time was recorded respectively to compare the grinding efficiency.The results of grinding efficiency were statistically analyzed.Three specimens were randomly selected in each group to observe the general characteristics and surface morphology.Part Ⅱ:Two types of monolithic zirconia specimens were fabricated by the same process as stated above.The specimens of each zirconia type were randomly assigned into 4 groups(n=10):as-sintered,ground by the extra fine-grit dimond bur,polished by the special zirconia polishing kit and polished by the general-purpose ceramic polishing kit.Surface morphology and roughness(Ra)were characterized,followed by one-way ANOVA analysis(α=0.05).Results:Part I:The grinding efficiency ground by the standard-grit diamond bur was 2.94±0.56 mm3/min for wet deposited zirconia and 2.19 10.10 mm3/min for dry milled zirconia.The grinding efficiency ground by the extra fine-grit diamond bur was 2.49±0.36 mm3/min mm3/min for wet deposited zirconia and 1.49±0.25 mm3/min for dry milled zirconia.The grinding efficiency of the standard-grit diamond bur was significantly higher than that of the extra fine-grit diamond bur.The grinding efficiency of wet-deposited zirconia was significantly higher than that of dry milled zirconia.The surface polished by the polishing brush was rougher than polished by the polishing kit.Part Ⅱ:The as-sintered wet-deposited zirconia exhibited a smooth surface with obvious different morphologies compared with the as-sintered dry milled zirconia(Ra:0.26 10.05 μm versus 0.33±0.10 μm).Ra of the ground wet-deposited zirconia was significantly higher than that of the as-sintered wet-deposited zirconia(P<0.001)and the ground dry-milled zirconia(P=0.011).For both types of zirconia,Ra decreased significantly after polishing(P<0.001),and there was no significant difference between the 2 groups with different polishing kits(wet-deposited zirconia-P=0.144;dry milled zirconia-P =0.322).Surface morphologies of both zirconia became similar after grinding and polishing.Conclusions:For both zirconia,the grinding efficiency of the standard-grit diamond bur was significantly higher than that of the extra fine-grit diamond bur.But short-time polishing can not eliminate the deep grinding ditches generated by the standard-grit diamond bur.Thus the standard-grit diamond bur was not recommended for clinical grinding.The polishing kit can effectively improve the rough surface generated by the extra fine-grit diamond bur.And the polishing effect of the polishing kit was better than that of the polishing brush.Thus the extra fine-grit diamond bur was preferred for grinding then the polishing kit was preferred for subsequent polishing.The grinding efficiency of wet-deposited zirconia was significantly higher than that of dry-milled zirconia.Wet-deposited zirconia fabricated by wet deposition exhibited a smooth surface with specific patterns compared with the dry milled zirconia.Grinding significantly changed the surface morphology of wet-deposited zirconia and increased surface roughness of both zirconia,which can be improved by polishing without being influenced by polishing kits selection.