Evaluation of the resistance to brushing abrasion of different polishing methods on monolithic zirconia surfaces

Purpose: The aim of this study is to evaluate the amount of surface roughness change after five years of brushing simulation in different monolithic zirconia (5Y-TZP) specimens with glaze or polishing. Materials and Methods: Four different brand monolithic zirconia sample groups (E.max ZirCAD/MT, Katana/HT, Vita YZ/HT, Cercon/HT) were designed to have 2×10×10 mm dimensions, were produced and sintered. Half of the samples were polished (OptraFine Polishing Set) and glaze was applied to the rest of the samples. Surface roughness was measured with an optical profilometer (Zygo Newview 7200) and atomic power microscope (MPF-3D Origin AFM). All test groups were then brushed 50,000 cycles with a toothbrush to simulate five years of brushing. After simulated brushing, the surface roughness of all test groups was again measured using an optical profilometer and AFM. Statistical analyzes were performed using the Shapiro Wilk test, Mann Whitney U test, Kruskal Wallis test and Post Hoc Bonferroni test. P≤0.05 was used as the significance value in the study. Results: Glazed or polished specimens in all test groups showed similar surface roughness values (Ra) before and after brushing simulation. Considering the Pv value, both glaze and polished groups had a less rough surface after brushing than before brushing (p≤0.05). The surface roughness did not change according to the Ra values, indicating that the average roughness value did not change, only the distance (Pv) between the highest peaks and the deepest valleys decreased. The lowest surface roughness values were obtained from the polished Vita brand sample groups, while the highest values were obtained from the glazed DDcube brand sample groups. Conclusion: Polished samples showed similar roughness values with glazed samples. For this reason, it was concluded that the polishing set used in the study was as effective as glazing on a monolithic zirconia surface, provided that it was applied taking into account the recommended instructions. However, it was concluded that the five-year brushing simulation did not have a positive or negative effect on the mean surface roughness in all tested 5Y-TZP monolithic zirconia specimens.