Effects of cavity designs on fracture behavior of mandibular first premolars with moderately curved C-shaped canal

This study was to analyze the fracture behavior of lower first premolars with moderately curved C-shaped canal using extended finite element method. After scanning mandibular first premolars with diverse types of moderately curved C-shaped canal with Micro-CT, models of the intact tooth, conservative endodontic cavity (CEC) and traditional endodontic cavity (TEC) were generated. A total load of 600 N was applied vertically to buccal cusp and buccal side of distal fossa for each model. Distributions of maximum principal stress (MPS) and crack evolution of enamel and dentin were evaluated. Larger stress concentration area and smaller crack initiation loads were found in root-filled teeth in enamel, especially TECs, and MPS was centralized around the distal fossa and heightened at distal side of cavity margins after preparation. In dentin, stress concentration areas and crack initiation loads were similar among groups. Stress was concentrated at the mesio-lingual surface or at the lingual surface and slightly towards the mesial side. The fracture originated in enamel, forming microcracks around distal fossa, then happened in dentin below the bone level. For lower first premolars with moderately curved C-shaped canal, cavity preparation mainly impacted the biomechanical response enamel, rather than dentin.