Effect of length of apical root resection on the biomechanical response of a maxillary central incisor in various occlusal relationships.

Abstract

To investigate the stress distribution and tooth displacement of a maxillary central incisor with various apical root resection lengths and occlusal relationships using finite element (FE) analysis. A maxillary central incisor was scanned by micro-CT. First, the FE intact incisor model with dentine, enamel, pulp and root surrounded by alveolar bone and periodontal ligament was designed based on the micro-CT image data. Then, six FE models with varying lengths of apical root resection were established to simulate the clinical treatment and reveal the clinically applicable limit of apical root resection during endodontic microsurgery. For each model under different loading conditions, the maximum von Mises stress (σ max) at the root apex, root cervix, alveolar bone and periodontal ligament and the maximum tooth displacement (ΔR max) were calculated and compared. In a normal occlusion, more than 6mm of root resection resulted in a marked increase in the ΔR max values (>10%) and σ max values of alveolar bone (>50%); the stress levels at the root apex increased dramatically when the apical root was resected more than 7mm. With increased overjet, apical root resection did not change the stress level markedly until it reached 8mm, but the ΔR max increased markedly (>10%) if the root was resected more than 5mm. With deep overbites, the σ max increased significantly (>50%) when the root was resected more than 4mm whilst the ΔR max decreased. With increased overjet and deep overbite, more than 6mm of resection resulted in a substantial σ max increase (>50%) of alveolar bone and the ΔR max increased markedly (>10%) when the root was resected 8mm. Additionally, the σ max and the ΔR max values were greater with increased overjet and lower with deep overbites. Using FE analysis, apical root resection of more than 6mm resulted in a marked increase of stress distribution and tooth displacement in normal and increased overjet with deep overbite occlusal relationships. In increased overjets or deep overbites, more than 5mm or 4mm, respectively, stress distribution and tooth displacement increased markedly.