Three Dimensional Finite Element Analysis Of The Mandibular Dentition Distal En-masse With Microscrew Implant Anchorage

Skeletal Class â…¢ malocclusion is one of most common malocclusion in clinically, owning to the complexity and individual variation of this type of malocclusion, Orthodontists have focused to choose an effective method to correct skeletal Class â…¢ malocclusion. Various treatments have attempted in clinic, including multiloop edgewise arch-wire(MEAW), class â…¢ intermaxillary traction, mandibular J hook, lip bumper and so on, while anchorage loss or poor patient compliance would result in unexpected therapeutic effect.Fortunately, the application of microscrew implant anchorage provided an new option to skeletal Class â…¢ malocclusion treatment. In clinic, microscrew implant anchorage can achieve favourable compensatory therapeutic effect via retracting single, grouped or the whole lower teeth.However, few studies was found on the biomechanical effect of the whole mandible dentition distal retaction with microscrew implant anchorage, so in this study, we established a 3D finite element model of distal en-masse movement of the mandibular dentition with microscrew implant anchorage, and subsequently we investigated thedistance of incisors and molars movement and stress of PDL, moreover, the rotating trend of occlusal plane was also analyzed, so as to provide some useful references for the microscrew implant anchorage application in clinic. Our study consist of three parts:Part 1: 3D finite element model of distal en-masse movement of the mandibulardentition with microscrew implant establishment.Objective: This study aim to establish a 3D finite element model including mandible, lower dentition, periodontal ligament, bracket, arch wires and microscrew implant anchorage. Methods: A adult with mesial occlusion relationship and slightly crowded lower anterior teeth was choose as a volunteer, the patient underwent spiral CT scanning, and then the CT datum was imported into Mimics 17.0 software. 3D model was established via following procedures, including threshold setting, manual erasion, 3D images generation and surface reconstruction. The 3D models of brackets, arch wires, traction hook and min-implant anchorage was generated via Unigraphics NX, furthermore, all of the established 3D models were assembled together and imported into ansys workbench software, 3D finite element model was established followed by model property definition, mapped meshing and boundary constraint. Results: 3D finite element model of distal en-masse movement of the mandibular dentition with microscrew implant anchorage was established successfully, which consist of 669571 elements and 1014160 nodes. Conclusions: It is feasible to establish 3D finite element model of distal en-masse movement of the mandibular dentition with microscrew implant anchorage via Mimics 17.0, Unigraphics NX and ansys workbench software.Part 2: 3D finite element analysis of the effects of distal en-masse movement of the mandibular dentition with microscrew implant anchorage while differ in the height of traction hook.Objective: The aim of this study was to analyze the effect of different height of traction hook on traction results when distal en-masse movement of the mandibular dentition with microscrew implant anchorage. Methods: Based on the 3D finite element model established in Part 1, when loaded with 3N force and the height of traction hookwere 2mm, 0mm,-2mm and-4mm, the initial displacements and force of lower dentition were calculated respectively. Meanwhile, the rotating trend of occlusion plane was also analyzed. Results: The distal displacement of lower anterior teeth declined gradually with the height of traction hook decreased from 2mm, 0mm,-2mm and-4mm, while the distal displacement of lower premolars and molars increased gradually. Moreover, The occlusion plane counterclockwise trend decreased gradually. Conclusions: the types of mandibular dentition movement changes with different ARH height. We can reduce and avoid the side effects by changing the height of ARH in different types anterior crossbite.Part 3: 3D finite element analysis of the effects of distal en-masse movement of the mandibular dentition with microscrew implant anchorage while posterior instruction.Objective: To investigate the biomechanical effect of distal en-masse movement of the mandibular dentition with microscrew implant anchorage when posterior instruction. Methods: Based on the 3D finite element model established in Part 1, the initial teeth displacement and the rotating trend of occlusion plane were analyzed with the height of traction hook decreased from 2mm, 0mm,-2mm and-4mm under 1.5N intrusion loaded. Results:1) When posterior teeth intrusion loaded on the same ARH height, the distal movement trend of incisors, canines, premolars teeth increased significantly, while the distal movement trend of molars teeth declined and vertical depressed. 2) The rotating trend of occlusion plane converted into counterclockwise. Conclusions: The types of movement of mandibular dentition changed when loaded instrusion force on posterior teeth.