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

Aim 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. Methodology 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 (sigma max) at the root apex, root cervix, alveolar bone and periodontal ligament and the maximum tooth displacement (Delta R max) were calculated and compared. Results In a normal occlusion, more than 6 mm of root resection resulted in a marked increase in the Delta R max values (>10%) and sigma max values of alveolar bone (>50%); the stress levels at the root apex increased dramatically when the apical root was resected more than 7 mm. With increased overjet, apical root resection did not change the stress level markedly until it reached 8 mm, but the Delta R max increased markedly (>10%) if the root was resected more than 5 mm. With deep overbites, the sigma max increased significantly (>50%) when the root was resected more than 4 mm whilst the Delta R max decreased. With increased overjet and deep overbite, more than 6 mm of resection resulted in a substantial sigma max increase (>50%) of alveolar bone and the Delta R max increased markedly (>10%) when the root was resected 8 mm. Additionally, the sigma max and the Delta R max values were greater with increased overjet and lower with deep overbites. Conclusions Using FE analysis, apical root resection of more than 6 mm 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 5 mm or 4 mm, respectively, stress distribution and tooth displacement increased markedly.