Comparative evaluation of effectiveness of three versus four mini-implants for simultaneous intrusion and retraction of maxillary anterior teeth: A 3D FEM study.

OBJECTIVE:To evaluate and compare the displacement pattern of maxillary anterior teeth in the sagittal and vertical planes and evaluate the stress distribution in pdl, bone, teeth of the maxillary anterior region, and around the mini-implants during simultaneous en-masse retraction and intrusion using two, three, and four mini-implants combinations. METHODS:A three-dimensional FEM model of maxillary teeth and periodontal ligament housed in the alveolar bone with extracted first premolarswasgenerated. The models were broadly divided into three groups according to the number of mini-implants. Mini-implants were placed bilaterally between the second premolar and molar in group I, and along with bilateral implants, an additional mid-implant was placed between the central incisors as in group II, whereas in group III, anterior mini-implants were placed in between lateral incisors and canine bilaterally. RESULTS:The two mini-implant model showed the maximum amount of retraction in the sagittal plane followed by three and four mini-implant models. In the vertical plane, all six anterior teeth showed intrusion only in the four mini-implant model. The stress in cortical bone, cancellous bone, PDL, around the mini-implants, and in lateral incisor was maximum in the three mini-implant model, followed by four mini-implants with the least stress in the two mini-implant model. CONCLUSION:The four mini-implant model is better than the three and two mini-implants model as there is a more even distribution of force in the four mini-implants model as compared to the three mini-implants model.