A Comparative Study on Simulated Chairside Grinding and Polishing of Monolithic Zirconia

Abstract

This study evaluated the effects of different simulated chairside grinding and polishing protocols on the physical and mechanical properties of surface roughness, hardness, and flexural strength of monolithic zirconia. Sintered monolithic zirconia specimens (15 mm × 3 mm × 3 mm) were abraded using three different burs: diamond bur, modified diamond bur (zirconia specified), and tungsten carbide bur, along with a group of unprepared specimens that served as a control group. The study was divided into two phases, Phase 1 and Phase 2. Surface roughness, surface hardness, and flexural strength were assessed before and after the grinding procedure to determine the ‘best test group’ in Phase 1. The best abrasive agent was selected for Phase 2 of the study. The specimens in Phase 2 underwent grinding with the best abrasive agent selected. Following the grinding, the specimens were then polished using commercially available diamond polishing paste, a porcelain polishing kit, and an indigenously developed low-temperature sintered zirconia slurry. The physical and mechanical properties were again assessed. Results were analyzed using one-way ANOVA test. Specimens were observed under scanning electron microscopy (SEM) and X-ray diffraction (XRD) for their microstructure and crystalline phases, respectively. Grinding with diamond burs did not weaken zirconia (p > 0.05) but produced rougher surfaces than the control group (p < 0.05). Tungsten carbide burs did not significantly roughen the zirconia surface. However, specimens ground by tungsten carbide burs had a significantly reduced mean flexural strength (p < 0.05) and SEM revealed fine surface cracks. Phase transformation was not detected by XRD. Polishing with commercially available polishing agents, however, restored the surface roughness levels to the control group. Dental monolithic zirconia ground with tungsten carbide burs had a significantly reduced flexural strength and a smooth but defective surface. However, grinding with diamond burs roughened the zirconia surface. These defects may be reduced by polishing with commercially available polishing agents. The use of tungsten carbide burs for grinding dental zirconia should not be advocated. Grinding with diamond abrasives does not weaken zirconia but requires further polishing with commercially available polishing agents.

Screwed Monolithic Zirconia Crowns for Mono-Implant Posterior Rehabilitation: A Prospective Clinical Study on 41 Patients with a 7-Year Follow-Up

“…This switch from Excellence to Success of this specific USPHS parameter was reported in two more patients, one in the sixth year and the last in the seventh year of evaluation. In every case, it was a slight entity that was resolved by polishing the surface, as suggested by Kheur et al [27]. The worsening of surface roughness is consistent with that found in previous studies [12,19,20], so it deserves to be studied further.…”

Prototype importance for implant supported zirconia bridges: a case report

“…Grinding with a diamond bur followed by polishing instead of reglazing helps retain the mechanical properties of the monolithic ceramic material. 22 Vila-Nova et al, concluded that that the use of diamond polyurethane rubber polishers is the most suitable method for adjusting monolithic zirconia restorations. Glazing after adjustments with diamond burs should be avoided, since it significantly reduces the fracture resistance of these materials.…”