Effect of Three-wall Bony Defect along Various Root Surfaces on Position of Center of Resistance: A 3D Finite Element Analysis.

INTRODUCTION Increase in adult orthodontic patients has increased the challenges faced by orthodontists, as they often present themselves with a varying degree of dental and peri-odontal compromise, in which the entire orthodontic treatment planning will revolve around maintenance and augmentation of supporting apparatus. One of the many factors to be considered during treating an adult patient is the height of alveolar bone and its effect on center of resistance (CRes). MATERIALS AND METHODS Eight 3D analytical models of upper central incisor were designed using 'Solid Works Office Premium'. The models were subjected to 3 and 6 mm bone loss along all four surfaces, i.e. labial, lingual, mesial and distal. One Newton of retraction force was applied on labial surface of tooth on model number 1, 2, 5 and 6 and 1N of distalization force was applied to model number 3, 4, 7 and 8. The relative location of the CRes to the total root length was taken as 41.8% of total root length from the root apex. The ANSYS software was used to evaluate the change in CRes on all the models. RESULTS It was observed that CRes shifted apically from its relative location (41.8% from apex); however, this shift was clinically insignificant. Minimum deflection of CRes, 0.0122 mm, was seen when a distalization force was applied on model with 6 mm bone loss on distal surface, while maximum deflection of 0.0245 mm was seen when retraction force was applied on model with 6 mm bone loss on labial surface. CONCLUSION The resultant displacement in position of center of resistance is negligible; hence, there is no need of changing biomechanics during orthodontic treatment for a tooth with three wall infrabony defects. However, it is necessary to further study other infrabony defects like two wall or one wall defect, and their effect on position of CRes.