Avaliação biomecânica da mandibulotomia

Abstract

Currently, cancer is still the cause of high death rates worldwide. Therefore, researchers are engaged in prevention and early diagnosis of this malignant disease that affects millions of people. Specifically in Brazil, it is recognized as a public health problem. Despide all efforts, the incidence of oral cancer in particular, is most often diagnosed in advanced stages. The mandibulotomy technique is used for surgical access of some tumors in this region.The surgical access to the tumors can be done using miniplates with titanium screws or steel wires systems. They are used to fixate the osteotomies and provide maximum stability for an appropriate osteosynthesis. However, there are many doubts regarding the best mounting configurations and biomechanical behavior related to the mandibulotomy technique. In this work, the technique using the fixation by miniplates and screws were evaluated in two ways: numerically, by means of the finite element method, and experimentally, for both midline and paramidline cut. Statistical analysis with Scott Knott method (p = 5%) was used to evaluate the experimental stability. The experimental data were used to validate the numerical models and, in sequence, the prediction equations for stability were obtained using similitude methods. The variables were optimized using genetic algorithms to allow indicate the best models that guarantee the best stability. The settings of mini plates and screws of these optimized models were applied to numerical models of a human jaw and compared with those conventional conditions used by surgeons in terms of stress and displacement levels. Considering midline mandibulotomy and measurements of relative displacement between osteotomy sides, the CM2M4I - P1P3 model (fixed with four screws and positioned internally to the osteotomy line with two miniplates placed, one in the lower and the other one little higher, a middle region of the mandible) showed better stability when compared to the conventional surgical one. The better stability condition of paramidline osteotomy was the CP2M4I - P2P3 model (fixed with four screws positioned internally in relation to the osteotomy line, with two miniplates located in the middle region of the mandible). In parallel, the union stability of the midline and paramidline osteotomies was also evaluated using fasteners with stainless steel wire. Actually, this stainless steel wire technique is in disuse and showed lower stability when compared to the miniplates and screws technique. It s conclude that some configurations of miniplate and screws can replace the conventional models currently used by surgeons.