A comparative evaluation of different compensating curves and power arm length during retraction of maxillary anterior teeth: A finite element study

Abstract

Introduction: The strategic design of an appliance for anterior retraction by using orthodontic mini-implant anchorage and sliding mechanics must take into account the height of the power arm and compensating curve in archwire. This study was conducted to analyze the change in maxillary anterior teeth displacement and stress distribution using different compensating curves in the arch wire and varying power arm length in first premolar extraction case during sliding mechanics. Materials and Methods: 6 geometric models were created using ANSYS software. This geometric model was converted into a finite element model with the help of software HYPERMESH 11.0. Bilaterally mini-implants were placed in the bone between the roots of maxillary second premolar and first molar. Power arms were placed at two heights – 3 mm and 5.5mm. Compensatory curves were placed in the archwire (0, 3mm or 5mm) and a force of 150 gms was applied using NiTi coil springs bilaterally. Stresses in bone and tooth displacements were analyzed. Results: There was more bodily movement of the teeth using the longer power arms. Incorporating a compensatory curve further helped to reduce tipping. The tooth that showed most bodily movement was the lateral incisor followed by central incisor and least by the canine. There was increased intrusion of the incisors and extrusion of canine with increase in power arm height. Conclusion: Increase in power arm height causes an increased intrusive tendency and increased bodily movement during en masse retraction of anterior teeth using mini- implant anchorage. Incorporation of a 5mm compensatory curve further helps reduce the tipping tendency of the anterior teeth.