Objective: Molar intrusion using orthodontic miniscrews placed at palatal side is a common mechanics to correct open bite. However, molar intrusion from palatal side causes lingual crown tipping of molars as undesirable side effect. Although buccal crown torque is certainly effective to prevent this phenomena, degrees of torque applied to archwire depend on practitioner’s experience. The objective of the present study was to clarify how many degrees of torque is required to control tipping of the molars on intrusion using finite element method (FEM).
Methods: We constructed a three dimensional finite element model of maxillary dentition. The model had 0.022-inch bracket system and 0.019 x 0.025 inch archwire. Intrusion force of 100 cN was applied to each of the first and second molars. 30, 40 and 50 degrees of buccal crown torque were tested to prevent lingual crown tipping of the molars. Simulation for long term tooth movement was performed using FEM. The simulation was stopped at the time when the first molar was intruded 2 mm.
Results: Lingual crown tipping of the premolars and first molar occurred even with 50 degrees of torque application. Buccal crown tipping of the second molar occurred only with 50 degrees of torque.
Conclusions: The results of the present study suggests that at least 50 degrees of torque is required to prevent lingual tipping of the molars in intrusion mechanics using orthodontic miniscrews on palatal side.