A Three-Dimensional Finite Element Method to Study the Changes in Centre of Resistance with Alveolar Bone Resorption

Introduction: Patterns of initial displacement of a tooth may be influenced by variables like alveolar bone, width of periodontal ligament space, and properties of the periodontium. Alveolar bone loss modifies biomechanical behavior of a tooth under orthodontic forces. Thus it is imperative to know optimal force considerations for patients with altered alveolar bone height. The aim of this study was to locate the centre of resistance and centre of rotation of maxillary central incisor at various stages of alveolar bone loss. Materials & Methods: A descriptive cross-sectional study design was used. The present study was conducted in the Department of Orthodontics and Dentofacial Orthopedics UCMS College of Dental Surgery, Bhairahawa. A 3-dimensional model of an upper central incisor was designed using ANSYS software in Pentium III computer. Five models of an upper central incisor with 1 mm to 8 mm of alveolar bone loss were created. The mechanical properties (Poisson’s ratio and Young’s Modulus) of the periodontal ligament, tooth and alveolar bone were considered. A force of 1N was applied to the labial surface of the tooth crown at each phase of the study at 5.5 mm apical to incisal edge (this was presumed to be the location of the bracket). The point of force application was centered mesiodistally. Results: The results revealed that alveolar bone loss resulted in apical shift of the centre of resistance. The centre of resistance was at 9.3 mm from the apex of the tooth, it shifted apically to 8.8 mm, 5.7 mm, 4.9 mm and 4.4 mm with bone loss of 1 mm, 5 mm, 6.5 mm and 8 mm, respectively. A greater amount of displacements of the incisal edge and apex were observed with increased alveolar bone loss for a constant applied force. The Moment/Force ratio required to produce bodily movement increased with alveolar bone loss. Conclusion: Alveolar bone loss led to a change in the centre of resistance as a result of alteration in bone support.