Evaluation of displacement and stress distribution on the teeth by three dimensional modelling and finite element analysis method of orthodontic forces applied by multi-vectorial anchorage (MVA) system

Anchorage control according to the treatment plan is one of the most important success criteria in orthodontics. Traditional methods (eg: Headgear, Nance, Transpalatal arch) that have been used for many years for anchorage purpose have some disadvantages, such as the need for laboratory steps and patient co-operation. More and more, temporary skeletal anchorage devices call attention of clinicians as an alternative method for anchorage control. Miniplates are able to withstand high orthodontic forces and they are placed in regions which are in safe anatomic neighborhood. Also, their stability is considerably higher than that of the other skeletal anchorage units such as mini-screws, and their usage for orthodontic purposes is worthwhile due to providing solutions for complex orthodontic problems. Orthodontic miniplates in various shapes and designs are offered for the choice of researchers and clinicians. Miniplates are generally consist of a body part fixed in cortical bone fixed with screws and an intraoral part for applying the orthodontic forces. Despite the high success rates of intra-osseous stabilization, traditional miniplates have some disadvantages such as soft tissue irritation in the oral regions, difficulty in attaching the force applicators to the miniplate, and also difficulty in chancing the force application point. In this thesis Project, a new miniplate has been designed to overcome all of these limitations. Soft tissue around the intraoral part of the miniplate is managed and formed by a healing cap. These healing caps are replaced by an abutment named as multi-vectorial anchorage abutment during the loading of the force. The arm unit of newly designed miniplate has holes and a button for attaching the force applicators. This arm unit is able to turn around 360 degrees and is fixed on the miniplate by the means of internal screws. The line of force application can be changed easily by alterating the angle of the arm, according to the desired type of the tooth movement. It is thought that peripheral tissue irritation, which leads to the loss of mini-plate fixation screws, can be prevented with healing caps providing better control of the soft tissues. In our study, the stress distribution of the forces applied from the designed miniplates on the teeth and the resulting displacements were evaluated by Three-dimensional Modeling and Finite Element Analysis Method. In the first three-dimensional model, first premolar extraction scenario was imitaded and a 150 gr distalization force was applied to the canine with different angulations of the miniplate arm (0°, 90°, 180°, 225°, 270°, 315°). In the second model, a total of 200 gr intrusive force was applied with 0 and 90 degrees angulated miniplate arms, vertically to the arch wire. The force was applied between the first premolar and the molar (100 gr) and between the first and second molars (100 gr). According to the results of the analysis, the highest amount of canine distalisation was observed at 180° and 225° angulated arms and minimum movement was observed at 0° and 90° degrees. It has been determined that the maximum amount of canine expansion in the transversal plane occures at 0° and 90° degrees angulation. During the distalisation movement of the canine, the intrusive movement due to the vertical component of the applied force was observed maximum at 0 degree and then at 90°, 270°, 315°, 225° and 180° degrees, respectively. As a result of the intrusion force applied on the second model; the highest value of intrusion movement was observed in the first molar and then in the second molar, additionally buccal tipping movements of these teeth occured. Decreasing amounts of intrusion and tipping movements have occurred in the canine and premolar teeth. Keywords; Skeletal anchorage, Miniplate, Finite element analysis, Canine distalization, Molar intrusion.