Effects of small-grit grinding and glazing on mechanical behaviors and ageing resistance of a super-translucent dental zirconia

Objectives: The purpose of this study is to elucidate the effects of small-grit grinding on the mechanical behaviors and ageing resistance of a super-translucent dental zirconia and to investigate the necessity of glazing for the small-grit ground zirconia. Methods: Small-grit grinding was performed using two kinds of silicon carbide abrasive papers. The control group received no grinding. The unground surfaces and the ground surfaces were glazed by an experienced dental technician. Finally, the zirconia materials were thermally aged in water at 134 degrees C for 5 h. After aforementioned treatments, we observed the surface topography and the microstructures, and measured the extent of monoclinic phase, the nano-hardness and nano-modulus of the possible transformed zone and the flexural strength. Results: Small-grit grinding changed the surface topography. The zirconia microstructure did not change obviously after surface treatments and thermal ageing; however, the glaze in contact with zirconia showed cracks after thermal ageing. Small-grit grinding did not induce a phase transformation but improved the flexural strength and ageing resistance. Glazing prevented zirconia from thermal ageing but severely diminished the flexural strength. The nano-hardness and nano-modulus of the surface layer were increased by ultrafine grinding. Conclusions: The results suggest that small-grit grinding is beneficial to the strength and ageing resistance of the super-translucent dental zirconia; however, glazing is not necessary and even impairs the strength for the supertranslucent dental zirconia. Clinical significance: This study is helpful to the researches about dental grinding tools and maybe useful for dentists to choose reasonable zirconia surface treatments.