Impact of Different Surface Treatments on Zirconia Strength

Abstract

Background: Intraoral polishing of zirconia surfaces had led to a significant increase in the surface smoothness and flexural strength of zirconia after surface modifications in the try-in procedure; this is a straightforward procedure and does not need any laboratory interventions. Objectives: The aim of this study was to evaluate the effect of different surface treatments on yttrium-stabilized zirconia restorations. Materials and Methods: In this study, 36 disk-shaped specimens from zirconia blocks were milled using a CAD-CAM machine with 12 mm diameter and 1.4 mm thickness for 27 disks; however, 12 mm diameter and 1.2 mm thickness were used for nine disks as a control group. They were sintered and glazed according to the manufacturer's instructions. The control group (GA) remained untouched, whereas the other specimens were ground with a diamond rotary instrument. The final dimension was 12 mm in diameter and 1.2 ± 0.1 mm in thickness. The disks were divided into three groups: Grinded group (GB) without any additional surface treatment; reglazed group (GC) by adding glaze material; and polished group (GD), polished with an intraoral polishing kit. The specimens were subjected to a biaxial flexural strength (BFS) test. Data were statistically analyzed using one-way analysis of variance and least significant difference (LSD) significant difference tests (a = 0.05). Results: Descriptive statistics shows that the highest BFS was recorded for the GD followed by GB, and both GA and GC show nearly similar values. The LSD tests revealed that there was a statistically significant difference between GD and GA (P < 0.05), GD had significantly increased the BFS value after being polished compared with other groups, and there was a statistically significant difference between GB and GA (P < 0.05). However, there was no statistically significant difference between GC and GA (P = 0.494). Conclusion: Grinding and polishing techniques significantly increased the flexural strength of full-contoured zirconia, whereas reglazing significantly decreased it.