Fracture Strength and Fracture Patterns of Root-filled Teeth Restored With Direct Resin Composite Restorations Under Static and Fatigue Loading

Aim: To assess fracture strength and fracture patterns of root-filled teeth with direct resin composite restorations under static and fatigue loading. Methodology: MOD cavities plus endodontic access were prepared in 48 premolars. Teeth were root filled and divided into three restorative groups, as follows 1) resin composite; 2) glass ionomer cement (GIC) core and resin composite; and 3) open laminate technique with GIC and resin composite. Teeth were loaded in a servohydraulic material test system. Eight samples in each group were subjected to stepped fatigue loading: a preconditioning load of 100 N (5000 cycles) followed by 30,000 cycles each at 200 N and higher loads in 50-N increments until fracture. Noncycled teeth were subjected to a ramped load. Fracture load, number of cycles, and fracture patterns were recorded. Data were analyzed using two-way analysis of variance and Bonferroni tests. Results: Fatigue cycling reduced fracture strength significantly (p<0.001). Teeth restored with a GIC core and a laminate technique were significantly weaker than the composite group (379 56 N, 352 67 N vs 490 78 N,p=0.001). Initial debonding occurred before the tooth underwent fracture. All failures were predominantly adhesive, with sub-crestal fracture of the buccal cusp. Conclusions: Resin composite restorations had significantly higher fracture strength than did other restorations. Fatigue cycled teeth failed at lower load than did noncycled teeth.