Enamel wear and aging of translucent zirconias: In vitro and clinical studies

Abstract

STATEMENT OF PROBLEM: Zirconia is a widely used restorative material. However, phase transformation on clinical application of zirconia has not yet been studied.

PURPOSE: The purpose of this study was to evaluate the wear, surface roughness, and aging associated with polished translucent zirconia in both in vitro and clinical experiments.

MATERIAL AND METHODS: In vitro experiments were performed with Rainbow and Katana zirconia blocks and natural tooth enamel as the control. They were subjected to 100 000 loading cycles with a maxillary premolar antagonist. All specimens were analyzed for wear, and the zirconia specimens were evaluated for surface roughness and monoclinic phase (m-phase) transformation by X-ray diffractometry before and after cyclic loading. The clinical study included participants who required single-crown implant-supported restorations replacing the first or second molar. The participants received Rainbow or Katana zirconia prostheses (n=15, each). For wear analysis, impressions of each prosthesis, antagonist, and adjacent tooth were made at 1 week and 6 months after crown delivery. The occlusal relationship of the crowns in maximum intercuspation was evaluated by using the T-Scan 8 occlusal diagnostic system. The degree of transformation of zirconia to the m-phase was measured by using X-ray diffractometry of the crowns after 6 months of use.

RESULTS: Zirconia induced significantly greater enamel wear than the natural tooth control. Katana specimens exhibited significantly greater wear and surface roughness than the Rainbow specimens. The degrees of antagonistic wear and zirconia phase transformation in the clinical experiment were significantly greater than those in the in vitro experiment. The Katana groups showed significantly higher m-phase levels than the Rainbow groups.

CONCLUSIONS: Phase transformation of zirconia occurs within 6 months of clinical use, and the wear and degrees of phase transformation varied according to the zirconia product used.