The Biomechanical Analysis Of Mandibular First Molar In Lingual Technique

ObjectiveWith the development of orthodontic techniques, more and more adult patients want to obtain the therapy of "Aesthetic Orthodontic". Therefore, the lingual technique has gained popularity with adult patients and attention of orthodontics for invisibility. Presently, there are many studies about successful treatment with lingual technique and the biomechanics of upper central incisor, and to the best of our knowledge, there are no published reports on the biomechanical of mandibular first molar. In this study, we established a finite - element model of mandibular first molar and simulated different kinds of orthodontic forces in lingual technique, to observe the movement and the stress response in the periodontium of the mandibular first molar, and to support a biomechanical basic for applying orthodontic forces in clinic.Methods1. Select sample: Select a healthy young man with whole teeth and normal morphology of the mandibular first molar, no minus, ranginge the normal place in the arch, good occlusion relationship with opposing teeth, normal contact with adjacent teeth, no peridontium disease, normal hight of alveolar bone.2. Take CT images: The volunteer take the poison of back lying having on occlusive board. The CT images were taken with 1mm intervals. Then scan the CT images with scanner and form a series of two dimension images.3. Read the CT images;Transform the CT images into BMP format and dealwith Photoshop 7. 0,read the boundary point with Matlab 6.0.4. Establish the three - dimensional finite element model: Establish the finite model with Ansys 6. 1. The model, comprising a mandibular first molar, PDL,and alveolar bone,consisted of 54138 nodes and 39160 isoparametric solid elements.5. Different types of loads were applied at the center of buccal and lingual surface , separately.6. Computerize and analyze the movement and the stress response in the periodontium of the mandibular first molar under different types of loads using Ansys.Results1. When the mesial force was applied to the mandibular first molar, it need to apply moments at the same time in order to obtain uniform low stress of the peridontium. In lingual technique, Mt/F =8.1:1 ,Mr/F =4.5: 1 ;In labial technique, Mt/F=9.5:1,Mr/F=5.7:l.2. When the intrusion force and extrusion force were applied,the vertical displacement of tooth were both smaller in labial technique than in lingual technique.3. When the mesial force was applied,the order of the maximum principal stress in PDL of different section were both: cervical region > furcation level > a-pex; the stress of cervical was: LO > BO, but in furcation level and apex were LO< BO; The stress of the tooth were both: cervical region > furcation level > crown> apex,and LO < BO.4. When the extrusion force was applied, the order of the maximum principal stress in PDL of different section were both: cervical region > furcation level> apex,and LO < BO;The stress of the tooth were both: furcation level > cervical region > crown >apex,and LO < BO.5. When the intrusion force was applied, the order of the maximum principal stress in PDL of different section were both: cervical region > furcation level> apex,and LO < BO;The stress of the tooth were both; cervical region >furca-...