The Three-dimensional Finite Element Study On Mesial Movement Of The Mandibular Second Molar

AIM: To construct a high precision3-D finite element model with dentition,PDL,mandibular, fixed appliance and dentition continuous ligation used in closing the spaceof lower first molar. To observe the ceep tendency and stress distribution in periodontaltissue by different force pattern by using the established model in second mandibularmolar mesial movement, which providing evidence for clinic.Methods：1. The elected healthy young woman mandibular CT scan line was derivedfrom direct cross-section image data transmission, processing, and three-dimensional(3D) model was generated. Divided grid, given mechanical parameters can be analyzedto establish the medical use of dentition, PDL, mandibular, fixed appliance and dentitioncontinuous ligation three-dimensional finite element model.2. The3D model wasloaded a force (F=150g) by different force pattern and different anchorage tooth withpreload a=0. To observe creep tendency and stress distribution in periodontal tissue.3.The3D model was loaded a force (F=150g) by different preload and different teeth withten anchorage tooth and the pattern of both sides simultaneously. To observe creeptendency and stress distribution in periodontal tissue.Result：1. The high precision FEM model, including mandibular teeth, periodontalsupporting tissue (periodontal ligaments, cortical bone, cancellous bone) and treatmentsystem, appliances (bracket, wire,“8” shaped ligation) was established (127158unites,249358nodes).2. The Von mises of the molar and anchorage tooth did not exceed26kPa with150g force. The stress in periodontal tissue gradually decreases with thenumber of anchorage increase. And the stress in periodontal tissue is smaller when we used the pattern of both sides simultaneously. Unilateral loading could easily lead to therotational movement of the molar anchorage tooth; bilateral loading could lead toinclined travelling of molar, and anchorage tooth have the same rotation trend, but theamount of displacement is smaller.3. The top value of stress concentrated area waslocated at the labial cervical margin. Apical stress is relatively small. In the case of10anchorage tooth and bilateral loading, the stress of the anchorage tooth is minimum anduniform, and the amount of initial displacement is least.4. In the case of preload a=0and the left first molar be loaded, the force of the periodontal tissue is smallest anduniformly. As the change of loading part, the stress concentration of premolar do notchange.Conclusion：1. The FEM model is high precision, which can simulate clinical well.2. Using150g force can effectively move the second mandibular molar, and are unlikelyto cause periodontal damage.3. The number of anchorage tooth should as much aspossible in second mandibular molar mesial movement. Using the loading of both sidessimultaneously can reduce the stress of anchorage tooth，but it leads to inclinedtravelling of molar. It requires us to use clinical class II elastic traction or backwardsong to offset this unwanted side effects in clinical work.4. We should minimize theforce about “8” shaped ligation and put the force site on first premolar.