Clinical performance of two onlay designs for molars after root canal treatment.

PURPOSE: To evaluate the clinical performance of two proposed onlay designs. METHODS: Molars with occlusal and/or mesial/distal defects after root canal treatment were classified by design into three groups. Onlays without shoulders were the control group (Group C, n = 50). The designed onlays were Group O (n = 50) and the designed mesio-occlusal/disto-occlusal onlays were Group MO/DO (n = 80). All onlays had an occlusal thickness of approximately 1.5-2.0 mm, and the designed onlays had a shoulder depth and width of approximately 1 mm. In Groups C and O, the box-shaped retention was 1.5 mm in depth. The proximal box was connected with a dovetail retention in Group MO/DO. Patients were examined every 6 months and followed for 36 months. Restorations were evaluated by using the modified United States Public Health Service Criteria. Statistical analysis was performed by using Kaplan-Meier analysis, the chi-square test, and Fisher's exact test. RESULTS: No tooth fracture, debonding, secondary caries, or gingivitis was observed in any group. Groups O and MO/DO had satisfactory survival and success rates, and there was no significant difference in performance characteristics among the three groups (P > 0.05). CONCLUSION: The two proposed onlay designs were effective in protecting molars.