Timing and method of restoration affect fracture resistance of endodontically treated teeth: An in vitro study

Root canal treatment (RCT) often results in significant loss of tooth structure, increasing the risk of tooth fracture under occlusal forces. This study aimed to evaluate the impact of different restoration timings on the fracture resistance of teeth after RCT and to compare the effectiveness of 3 restoration methods: full crown, onlay, and occlusal veneer. Sixty extracted human molars underwent standardized RCT and were randomly assigned to 9 groups (n = 6-7) in a 3 × 3 factorial design: immediate (1 week), early (2-3 weeks) or delayed (4-6 weeks) restoration, each receiving either a zirconia full crown, lithium-disilicate onlay or composite occlusal veneer. After thermomechanical aging (5000 thermal cycles, 50000 chewing cycles, 50 N), specimens were loaded to fracture (1 mm min-1). Mean fracture loads declined with delayed restoration: immediate 2 356 ± 413 N, early 2 086 ± 389 N, delayed 1 754 ± 357 N (P < .001). Full crowns resisted highest loads, followed by onlays and veneers (P < .01); timing × method interaction was significant (P = .038). Immediate restoration yielded 85% repairable failures; delay increased non-repairable root fractures to 55% (P = .004). Earlier restoration after RCT significantly enhances fracture resistance and clinical prognosis. While full crown restoration offers superior protection, onlay and occlusal veneer are viable alternatives that balance fracture resistance and tooth structure preservation.