In vivo wear of enamel by a lithia disilicate-based core ceramic used for posterior fixed partial dentures: First-year results

Purpose: This study aimed (1) to test the hypothesis that no significant relationship exists between the magnitude of occlusal clenching force and wear rates of enamel opposing a new core ceramic (e.max Press, Ivoclar Vivadent) used in posterior fixed partial dentures (FPDs); and (2) to test the hypothesis that mean annual enamel wear by an experimental core ceramic is comparable to the mean annual enamel wear by enamel of 38 mu m. Materials and Methods: Baseline data were obtained for patients in addition to preliminary impressions of maxillary and mandibular teeth. Thirty ceramic FPDs were processed from a new core ceramic (e.max Press) that was hot pressed and glazed. Patients were recalled 1 year after cementation and evaluated using clinical criteria that included wear assessment of opposing teeth. Impressions were made of the opposing teeth with polyvinyl siloxane impression material and photographs were taken of intraoral occlusal contacts marked with articulating ribbon. Baseline casts and casts made at each recall exam of opposing dentitions were scanned using a 3-dimensional laser scanner (Laserscan 3D, Willytec) and evaluated for wear. A total of 21 occlusal surfaces were analyzed for the presence of wear. Results: Statistical analysis using a linear and quadratic model revealed no significant relationship between occlusal forces and wear rate assuming either a linear model (R-2 = 0.018) or a quadratic model (R-2 = 0.023). The maximum annual wear of enamel by the glazed core ceramic (e.max Press) was 88.3 mu m, which is significantly greater than the annual enamel-by-enamel wear of 38 mu m (P <.0001). Conclusion: Further analysis with a larger sample size is needed to determine the relationship between occlusal clenching force and wear rate and the influence of other factors that cause increased wear of enamel by opposing ceramic restorations.