An In-vitro Evaluation of Grinding and Polishing on Surface Roughness and Flexural Strength of Monolithic Zirconia

Abstract

Introduction: For a dentist, it is a matter of concern to restore the original luster or glaze on a Monolithic Zirconia (MZ) restoration after clinical adjustments. For a long time, the gold standard for surface restoration was reglazing; however, with advancements in technology, new polishing kits optimised for zirconia have become available for chairside polishing. Aim: To examine the effects of grinding, reglazing, and polishing techniques on the surface roughness and flexural strength of MZ specimens. Materials and Methods: This in-vitro study was conducted in the Department of Prosthodontics at MM College of Dental Sceiences and Research in Mullana, Haryana, India from April to December 2019 and 32 specimens of MZ, each measuring 20 mm × 5 mm × 3 mm, were fabricated and divided into four groups, with each group consisting of eight specimens. Group C was considered the Control group. Specimens in Group G were only Ground, specimens in Group GR were Ground and Reglazed, and specimens in Group GP were Ground and Polished using a zirconia polishing kit. All specimens were then analysed for surface roughness and flexural strength using a profilometer and a Universal Testing Machine (UTM), respectively. Statistical analysis was performed using Analysis of Variance (ANOVA), Honest Significant Test (HSD) post-hoc test, Pearson’s correlation, and other methods using International Business Machine (IBM) Statistics version 25.0 (Armonk, USA). Results: The surface roughness (Ra) of the control group (C) was 0.4403 μm, followed by the Polished Group (GP) at 0.656 μm and the Reglazed Group (GR) at 0.809 μm. The difference between the polished (GP) and reglazed (GR) groups, was statistically insignificant (p=0.53). There was a statistically significant increase in flexural strength in the reglazed samples (GR) when compared to the polished samples (GP). No significant correlation (p=0.58 and r=-0.1) was found between surface roughness and flexural strength. Conclusion: Chairside polishing can be an effective alternative to reglazing for restoring the surface finish of MZ. Additionally, polishing increases the strength of zirconia after adjustments.

Keywords

• glaze
• mechanical properties
• post-processing