Influence of clinical finishing procedures and aging on zirconia roughness

Objectives: Full-contour monolithic zirconia restorations are being used to eliminate porcelain chipping observed with veneered zirconia. However, due to the high hardness of zirconia, there are concerns about clinically adjusting and polishing zirconia to an acceptable surface and the subsequent effect of aging on the adjusted surface roughness that could impact antagonist occlusal wear. The objective was to assess effects of different clinical finishing procedures on the surface roughness of zirconia before and after simulated aging.
Methods: Zirconia specimens (10x7x6mm slabs) prepared from Y-TZP blocks (Sirona InCoris) were assigned to 5 groups (n=7/group): control-glazed only and 4 treatment groups based on varied surface grinding/polishing protocols. Initial adjustment/grinding was done using a coarse or fine diamond with or without water irrigation, followed by polishing using a coarse and then fine diamond-interspersed rubber polisher with/without water irrigation at specified handpiece rpm. Surface roughness was evaluated quantitatively using atomic force microscopy (AFM) and profilometry before and after simulated aging. Representative specimens from each group were imaged for SEM qualitative analysis.
Results: Based on AFM, there was no significant difference in roughness (p>0.05) between any of the groups either before or after aging. In contrast, based on profilometry, specimens adjusted using coarse-diamond with/without water were significantly rougher (p<0.05) before and after aging than other groups, while fine-diamond/water-adjusted specimens demonstrated lowest roughness. In addition, the course-diamond adjusted specimens exhibited microcracking not observed with other groups.
Conclusions: AFM evaluation at the nanoscale did not reflect roughness damage observed with coarse-diamond adjustment suggesting profilometry was a more informative evaluation technique. Clinically, increased roughness and microcracking from coarse-diamond adjustment could lead to increased wear and potentially affect restoration longevity; fine-diamond adjustment with water is recommended. Lastly, while short-term simulated aging did not impact surface roughness, long-term aging studies would be beneficial. Funded by UMKC SOD Summer Scholars program.