Influence of adhesive techniques on fracture resistance of endodontically treated premolars with various residual wall thicknesses

Statement of problem The choice of restorative method is commonly based on the cavity configuration and the residual number of cavity walls. However, the residual wall thickness could be a valuable clinical parameter in the choice of restoration for endodontically treated teeth. Purpose The fracture resistance of endodontically treated premolars was compared with different wall thicknesses restored with direct composite resin with and without cuspal coverage and with and without fiber post insertion. Material and methods This study included 104 intact human maxillary premolars extracted for periodontal or orthodontic reasons. Standardized mesio-occluso-distal cavities were prepared with different palatal wall thicknesses (1.5, 2, and 2.5 mm) and a buccal wall thickness of 2 mm. Teeth were restored with or without a fiber post and with or without cuspal coverage. Specimens were subjected to thermocycling (3000 cycles, 5 to 55°C) and embedded in polymerized acrylic resin. Teeth were submitted to cyclic fatigue followed by a static fatigue test with a universal testing machine; a compressive force was applied 30 degrees to the long axis of the teeth until fracture. The results were statistically analyzed by 3-way ANOVA (α=.05). Results Residual wall thickness (P=.004), the type of adhesive restoration (P<.001), and fiber post insertion (P<.001) significantly influenced the fracture resistance of endodontically treated premolars. Conclusions In specimens with a cavity wall thickness >2 mm, direct intracuspal composite resin restorations supported by a fiber post achieved comparable fracture resistance. With a residual wall thickness <2 mm, only cuspal coverage with or without a fiber post provided satisfactory fracture resistance.