Effect of labiolingual inclination of a maxillary central incisor and surrounding alveolar bone loss on periodontal stress: A finite element analysis

Objective: The aim of this study was to investigate whether labial tooth inclination and alveolar bone loss affect the moment per unit of force (M_t/F) in controlled tipping and consequent stresses on the periodontal ligament (PDL). Methods: Three-dimensional models (n = 20) of maxillary central incisors were created with different labial inclinations (5º, 10º, 15º, and 20º) and different amounts of alveolar bone loss (0, 2, 4, and 6 mm). The M_t/F necessary for controlled tipping (M_t/F_cont) and the principal stresses on the PDL were calculated for each model separately in a finite element analysis. Results: As labial inclination increased, M_t/F_cont and the length of the moment arm decreased. In contrast, increased alveolar bone loss caused increases in M_t/F_cont and the length of the moment arm. When M_t/F was near M_t/F_cont, increases in M_t/F caused compressive stresses to move from a predominantly labial apical region to a palatal apical position, and tensile stresses in the labial area moved from a cervical position to a mid-root position. Although controlled tipping was applied to the incisors, increases in alveolar bone loss and labial tooth inclination caused increases in maximum compressive and tensile stresses at the root apices. Conclusions: Increases in alveolar bone loss and labial tooth inclination caused increases in stresses that might cause root resorption at the root apex, despite the application of controlled tipping to the incisors.