Comparison of Mini-implants Placed at Different Heights and Angulations for Retraction and Intrusion of Maxillary Incisors: A Finite Element Model Study

Abstract

Introduction Space closure is the most common treatment mechanic used in orthodontics in clinical practice. It can be done with friction and frictionless mechanics, and nowadays by using mini-implants. These mini-implants provide an absolute source of anchorage to obtain dental and soft tissue changes that are desired, thus helping to improve the patient’s profile. Aims and Objectives To evaluate the stress distribution patterns in the tooth, bone, and periodontal ligament in mini-implants placed at different heights and angulations for retraction and intrusion of maxillary incisors using finite element model (FEM). Materials and Methods FEMs of maxillary teeth and periodontal ligament housed in alveolar bone with the first premolars extracted were constructed. These models were further divided into two groups based on the number of implants. In group I, two implants were placed bilaterally between the second premolar and first molar at variable heights (7, 10, and 13 mm) and at different angulations (45° and 60°) to the long axis of the occlusal plane. In group II, along with the two bilateral mini-implants, an additional mid-implant was placed between two central incisors. These models were simulated using ANSYS 19.2 version software. Results The maximum distribution of stress (MPa) in hard bone, soft bone, and implant was seen in the FEM 7 model and was 17.65, 0.210, and 61.62 MPa, respectively, during the retraction and intrusion of maxillary anterior teeth. The highest stress distribution (MPa) was seen in the lateral incisor tooth in FEM 7 model (0.748 MPa) and also in the periodontal ligament around the lateral incisor in FEM 7 model (0.684 MPa). Conclusion The stress distribution was found to be highest in the lateral incisor tooth, periodontal ligament of the lateral incisor, and hard bone. The stress distribution pattern showed variation with different heights and angulations of the mini-implant. As the angle of insertion of the mini-implant to the long axis of the occlusal plane increases, the stresses generated in the bone decrease.