Biomechanical evaluation of maxillary protraction with an orthodontic anchor screw: a three-dimensional finite element analysis

Purpose The purpose of this study was to biomechanically evaluate maxillary protraction using an orthodontic anchor screw. We conducted three-dimensional finite element analysis to determine the initial displacement and stress distribution during maxillary protraction by comparing a conventional method involving fixation on teeth with maxillary protraction using an orthodontic anchor screw.Materials and methods We used X-ray computed tomography data obtained from Hellman Dental Age IIIA dry human skulls to create a skeletal anchorage model and a dental anchorage model as finite element models. In each model, a load of 6 N was applied in the anteroinferior direction at 0°, 10°, 20°, 30°, and 40° to the occlusal plane by means of a traction hook and the initial displacement and stress distribution were analysed.Results For the anterior nasal spine (ANS) sagittal displacement was greater in the skeletal anchorage model than in the dental anchorage model. In the central incisors and first molars, greater sagittal displacement was observed in the dental anchorage model compared with the skeletal anchorage model. In both models, vertical displacement was 20°, indicating maximum suppression of rotation in the maxilla. The zygomaticomaxillary and zygomaticofrontal sutures demonstrated high stress at 0° and 10° in the dental anchorage model, and at 20°, 30°, and 40° in the skeletal anchorage model.Conclusions These results indicate that tooth and bone–borne maxillary protraction using an orthodontic anchor screw inserted in the palatal region may be of value for the early mixed dentition period in patients with maxillary deficiency.