Effect of remaining tooth structure on the fracture resistance of endodontically-treated maxillary premolars: An in vitro study.

STATEMENT OF PROBLEM: Assessing the quantity and distribution of residual coronal dentin is important in deciding the restorability of endodontically treated teeth. PURPOSE: The purpose of this in vitro study was to investigate the relationship between the cross-sectional area and location of remaining coronal tooth structure and the fracture resistance of restored teeth after endodontic treatment. MATERIAL AND METHODS: Fifty-five extracted maxillary premolars received endodontic treatment and crown preparations. The teeth were assigned to 11 groups of 5 teeth according to the number and the location of missing axial walls. Impressions of the prepared teeth were made to fabricate dies. Each die was sectioned 1 mm above the finish line, and the dentin surface area was measured. All teeth were restored with composite resin cores and cast metal crowns. The specimens were thermocycled between 5 degrees C and 55 degrees C for 500 cycles before loading until failure with a universal testing machine. The results were analyzed with 1-way ANOVA and post hoc comparisons. RESULTS: Specimens with all axial walls intact around the access cavity had the highest mean fracture strength (1380.5 +/-393.9 N). Groups with the palatal and 1 or 2 proximal walls missing showed the lowest mean failure loads (398.4 N +/-149.5 N and 344.7 N +/-91.2 N). The correlation between the surface area and the fracture resistance was 0.72 CONCLUSIONS: For restored endodontically treated maxillary premolars, a positive linear relationship was found between the remaining coronal dentin surface area and fracture strength. Residual dentin location influences fracture resistance.