Biomechanical analysis of the maxillary molar intrusion: A finite element study.

INTRODUCTION: The purpose of this study was to analyze and clarify tooth movement when intruding the maxillary molars using intrusive forces between the maxillary first and second molars. METHODS: A finite element method was used to simulate the long-term orthodontic movement of the maxillary dentition by accumulating the initial displacement of teeth produced by elastic deformation of the periodontal ligament. Intrusive forces of 2 N were applied buccally to the archwire between the maxillary first and second molars. Two different sized transpalatal arches (TPAs) (0.036-in and 0.06-in) and a gradually increased constriction bend and torque toward the posterior teeth were applied to prevent buccal tipping of the posterior teeth when intruding the maxillary posterior teeth. RESULTS: The whole maxillary dentition rotated clockwise as the intrusive force passed posteriorly to the center of resistance. Buccal crown tipping of the maxillary posterior teeth and lingual tipping of the maxillary incisors occurred. Their tipping decreased with a constriction bend and lingual crown torque and when a TPA was applied. CONCLUSIONS: Supplemental procedures such as a constriction bend and lingual crown torque and a TPA could effectively prevent the buccal crown tipping of the maxillary posterior teeth when intruding on them.