The Analysis Of Occlusal Contact Types Of Mandibular First Molar And The Research Of Stress By The Finite Element Analysis Among Different Molar Relationships

Objective: To analyze the differences of the number and type of theocclusal contact on the first mandibular molar among different molarrelationships, meanwhile, explore the feasibility of this method. Toestablish the three dimensional finite element model of mandibular firstmolar which including the tooth and periodontal tissues and choosedifferent occlusal contact as loading parts according to the results which getfrom the cone beam CT studying results, simulating the loading situation oftooth and periodontal tissue under different occlusal contact types, it couldbe a occlusal adjustment guidance and help the orthodontic treatment,meanwhile it could help find the best type of occlusal contact.Method: There were347patients enrolled with inclusion andexclusion, who needed cone-beam CT examination in January2013to June2013in our hospital. The distribution of ABC contact in three types ofmolar relationship were recorded and analyzed with SAS9.2. Established athree dimensional finite element model of mandibular first molar, gave force to different occlusal contact with ANSYS analysis of cone beam CTresults, and analyzed the differences of tooth and periodontal tissue undervertical loading of21working conditions.Result:1. Compared the total numbers of occlusal contact of the three types, typeⅠand typeⅡ had no significant differences, but typeⅢ are less thanothers, and the differences were significant (P<0.0167).2. Compared the numbers of mesial contact, we found that typeⅡ>typeⅠ>typeⅢ, and the differences were statistically significant (P<0.0167);compared the numbers of middle contact, we found that type Ⅲ was theleast one, others had no significant differences; compared the numbers ofdistal contact, we found that type Ⅲ <type Ⅰ(P<0.0167), others had nosignificant differences.3. Compared the numbers of A and C contact, we found that type Ⅲ <typeⅠ,others had no significant differences; compared the numbers of Bcontact, we found that type Ⅲ was the least one (P<0.0167), others had nosignificant differences.4. The stress extreme values of ABC contact in typeⅠunder verticalloading were the least. The stress extreme values of C contact in typeⅡwere the largest, were40.613MPa.5. ABC contact type had the least displacement extreme values, however ithad the largest displacement either A or C as the only contact area. 6. The maximum principal stress and tensile stress extreme values of BCcontact in typeⅡappeared on the middle buccal surface of mesial root,while the rest appeared on the distal adjacent cervical region. Thecompressive stress extreme values appeared on the mesial adjacent cervicalregion.Conclusion:1.Cone beam CT could be a more direct and accuracy method in measuringthe types and the numbers of occlusal contact.2.The numbers of total occlusal contacts and the B contact in type Ⅲ werethe least, intercuspal relation had the worst occlusal stability.3.The von-mises stress of typeⅠwere the least with loading. The von-misesstress is bigger in three types with only A contact or C contact.4.According to the stress analysis about the tooth and periodontal tissue,ABC contact in typeⅠand type Ⅱ were best, while, A contact only or Ccontact only were worst.