Objective: The aim of this study was to investigate whether labial tooth inclination and alveolar bone loss affect the moment per unit of force (Mt/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 Mt/F necessary for controlled tipping (Mt/Fcont) and the principal stresses on the PDL were calculated for each model separately in a finite element analysis. Results: As labial inclination increased, Mt/Fcont and the length of the moment arm decreased. In contrast, increased alveolar bone loss caused increases in Mt/Fcont and the length of the moment arm. When Mt/F was near Mt/Fcont, increases in Mt/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.
Bibliographical noteFunding Information:
Acknowledgments. This work is funded by National Basic Research Program (Grant No. 2004CB318100), National Natural Science Foundation of China (Grant No. 60736018, 60702024, 60723005), and National Hi-Tech R\&D Program (Grant No. 2006AA01Z193, 2007AA01Z162).
© 2016 The Korean Association of Orthodontists.
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