Comparison of conventional methods of simultaneous intrusion and retraction of maxillary anterior: a finite element analysis.

OBJECTIVE: To study the biomechanical effects of the three-piece intrusion arch and Kalra simultaneous intrusion and retraction arch (K-SIR) on simultaneous intrusion and retraction of maxillary anterior teeth. DESIGN: Three-dimensional analysis of stresses and displacement of the anterior and posterior teeth with the three-piece intrusion arch and K-SIR arch was done using the finite element method (FEM). SETTING: Department of Orthodontics, Surendera Dental College and Research Institute, India. MATERIAL AND METHODS: For this investigation, the geometric model of the maxilla was constructed using a computed tomography scan. 0.022 × 0.028-inch MBT brackets and molar tubes were modelled, with the specified tip and torque values for all maxillary teeth. The wire components for the three-piece intrusion arch and K-SIR arch were modelled initially as a line diagram and then converted to three dimensional models. The material characteristics which include the Young's modulus and Poisson's ratio were assigned. After defining the boundary conditions, force systems were applied as per design. The analysis was carried out using ANSYS Version 12.1 software. The von Mises stress, principal stress on PDL and alveolar bone, change in the inclination of incisors and initial displacement of the teeth in bucco-palatal, mesio- distal and vertical direction were analysed. RESULTS: Stresses in cortical bone were greater than cancellous. Both modalities showed intrusion of the anterior teeth, although this was slightly more in the three- piece intrusion arch. On studying the principal stresses in the PDL, the three-piece intrusion arch displayed uniform stress distribution compared to K-SIR arch. CONCLUSION: The FEM cannot reflect actual biological responses within the human body to orthodontic forces but based on these findings, the three-piece intrusion arch showed better stress distribution and controlled tooth movement than the K-SIR arch.