Evaluation of initial displacement and stresses in the maxillary dentition following en masse retraction using fixed lingual appliance and micro-implants: A finite element analysis

Objective > To evaluate and compare the stress and displacement pattern between conventional and micro-implant supported retraction in lingual orthodontic system. Materials and methods > A finite element model of the maxilla, teeth, periodontal ligament, lingual-orthodontic appliance and a micro-implant complex was constructed using ANSYS 12.1 software. Two sizes of micro-implants, 6 mm and 8 mm, were constructed producing a simulated model of 99,190 nodes and 32,4364 elements. A retraction force of 200 g was applied from an anterior retraction hook to the molar tube in the conventional model and from the micro-implants in the implant supported model. The initial displacement and stress patterns in the X-Y-Z axes were obtained using Hyper-view software. Results > The maximum von Mises stresses in the 6 mm, 8 mm and conventional model were 22.164 Megapascals (MPa), 28.603 MPa and 16.491 MPa respectively. The bucco-lingual displacement of the maxillary anteriors was greater in the 8 mm implant model with 23 x 10(-3) mm lingual displacement observed. The least lingual displacement of 11 x 10(-3) mm was noted for the conventional model while a slightly higher moderate reading of 15 x 10(-3) mm was seen in the 6 mm micro-implant supported model. The maximum displacement of the periodontal ligament was noted in the 8 mm micro-implant model. Conclusion > Within the limitations of this research, the 8 mm micro-implant model displayed high initial stresses and greater initial displacement of the anterior teeth in the X-Y-Z coordinates in comparison to conventional retraction method.