Objective: Posterior intrusion had been one of the most difficult issues in orthodontics because of the lack of convenient anchorage. With the application of mini-implants as anchorage units, patient cooperation has been eliminated and side effects are reduced to a considerable degree. The aim of this study is to consider the effects of two maxillary posterior intrusion mechanics with mini-implant anchorage by finite element analysis.
Material and Method: Digital model of maxillary bone was generated by assembling computed tomography images. Teeth, brackets, mini-implants and arch wires were generated with a laser surface scanner and modelling software. In the first model intrusive forces were loaded to the posterior dental segment from four mini-implants which were placed in the vestibular and palatal side of the alveolar bone, two on each side. In the second model the forces were applied from two mini-implants placed in the vestibule alveolar bone and in order to balance the moments produced, two transpalatal arches were constructed.
Results: In both models, increased stress values were observed at the apical region of the first premolar roots and first molar mesial root. In the first model, intrusion was more balanced and the stress values were lower. In the second model the vestibular tipping movement was more prominent.
Conclusion: Simultaneous intrusive force application from vestibule and palatinal rather than TPA usage, lead to a more uniform intrusion and stress distribution. Apical region of the first premolar roots and first molar mesial root should be considered as highly susceptible to root resorption.