Numerical Simulation Of The Biomechanical Behavior During Orthognathic And Orthodontic Treatment

Dento-maxillofacial deformity means that the maxillofacial components of an individual deviates from the normal position due to innate or acquired factors,and severe cases can cause obvious dysfunctions.Patients need to receive orthognathic and orthodontic treatment together if they want to function well and look pretty.The numerical method can be used to reconstruct the 3D model of the dental maxillofacial structure and to simulate the clinical orthognathic and orthodontic operation.It can also be employed to analyze the biomechanical changes of the biology components during preoperative,intraoperative and postoperative periods.The first part of this thesis investigates the suitable occlusal forces that patients are allowed to apply after mandibular advancement surgery with bilateral sagittal split ramus osteotomy(BSSRO).The BSSRO has become a common surgical treatment for mandibular prognathism,retrognathism and asymmetry.Computed tomography(CT)scan images of a retrognathia patient are assembled to build a high resolution geometry model including the mandible,articular discs,the glenoid fossa and related tissues,then the BSSRO virtual surgery is carried out and the four different fixation devices are used.The muscles attached to the mandible are considered to simulate the occlusion condition of the maxilla and the mandible,and static analysis is carried out in this simulation.Results show that the stress distributions on the discs and the mandible exceed the normal level largely,while the displacement pattern maintains a normal level.Therefore,the suitable occlusal forces can be determined by the criterion of sustaining a normal stress level on the articular discs and the mandible.Of all the four fixation devices,the fixation system of three bicortical screws in an inverted L configuration allows patients to apply the maximum occlusion force(37% of the normal occlusal force),while the fixation system of three bicortical screws in line allows patients to apply the minimum occlusion force(23% of the normal occlusal force).The second part of this thesis aims to study the application of the appropriate orthodontic forces that used to close the extraction space during orthodontic treatment based on a finite element analysis model.The orthodontic tooth movement(OTM)is the result of biomechanical responses of the alveolar bone and related tissues.The modeling method in this part is the same as that in the first part,and finally the 3D model including the cancellous bone,the cortical bone,the periodontal ligament(PDL),the canine,the second premolar and the orthodontic devices is obtained.In order to make the canine have a translation movement to the extraction space,different orthodontic forces are applied on the bottom of the bracket and to the hooks that have different lengths.The hydrostatic pressure on the PDL is acted as the criteria to trigger the alveolar bone remodeling.The numerical results show that the canineleans to the distal side when orthodontic forces apply on the bottom of the bracket and in this case,the minimum orthodontic force needed to trigger the bone remodeling is 1.07 N.The canine is able to have a translation movement if the orthodontic forces apply on a 3 mm–length hook and in this case,the minimum orthodontic force needed to trigger the bone remodeling is 1.41 N.This thesis numerically studies the suitable occlusal forces that patients are allowed to apply after mandibular advancement surgery with BSSRO and also studies the application of the appropriate orthodontic forces that used to close the extraction space during orthodontic treatment.The numerical results presented in this study are helpful to orthodontic consultation.