STUDY OF THE STRESS-STRAIN STATE OF THE "FILLING-TOOTH" SYSTEM IN CERVICAL DEFECTS OF THE TEETH.

The problem of preserving restorations in defects in the cervical region, even with high-quality preparation and restoration, is also relevant in the modern world. The tensions in the teeth lead to the formation of cracks in the enamel and dentin, loss of tightness and marginal adhesion of the fillings, resorption and loss. Therefore, to ensure high-quality results of treatment of hard tissue defects in the cervical region of the teeth, it is appropriate to take into account the physical processes occurring around the "filling-tooth" system, namely, the stress-strain state. To assess the stress-strain state of the coronal part of the teeth with restorations, given the tightness and extreme cumbersomeness of using traditional analytical methods of theoretical mechanics and resistance of materials through a variety of geometric shapes and physical and mechanical characteristics of hard tissues of the dentition and filling material, it seems most appropriate to conduct research with using finite element modeling. The purpose of this biomechanical analysis is to study the influence of the size and location of defects of the cervical region on the stress-strain state of the obturation material in cases of restoration of these defects. Biomechanical analysis of the stress-strain state of the filling material was performed using elastic three-dimensional models of single-rooted teeth (first premolar and canine) fixed in the alveolar bone with periodontal ligaments surrounding the tooth root. Mathematical modeling was performed using the well-known modeling package and finite element analysis FEMAP 10.2.0, designed for implementation in the Windows environment on a personal computer. In order to reduce the number of finite elements, and as a consequence, reduce the amount of computational procedures and the amount of time spent on the calculation while increasing the accuracy of calculations, further research seems appropriate not on the full model of the mandible, but on its fragment isolated from the mandible. the first premolar and canine. Biomechanical analysis of the stress-strain state was performed on a fragment of the jawbone with overall dimensions of the cross section, which corresponds to some average dimensions: height h = 22 mm and width b = 16 mm. The program, which is used to build and analyze the considered models on the basis of the finite element procedure, determines the displacement of each node of the finite element along three coordinate axes, normal and tangential stresses, as well as equivalent Huber-Mises stresses. As the main criteria for assessing the stress-strain state of the obturation material, it is advisable to take the maximum values of tangential stresses at the adhesion boundary, which shift the filling material relative to the boundary of the restored cavity and thus determine the strength of the adhesive layer and, consequently, durability. The most unfavorable of the considered combinations of loads was the joint action of the vertical component of the load with the horizontal in the lingual-vestibular direction (corresponding to the maximum value of tangential stresses at the adhesion of the filling material) in the localization of restoration on the vestibular surface in the cervical premolar. When localizing the restoration on the oral side of the cervical premolar, the most unfavorable of the considered combinations of loads was the joint action of the vertical component of the load with the horizontal in the vestibular-lingual direction. Thus, the direction of action of the horizontal component of the functional load, in the most unfavorable combination with the vertical, is determined by the localization of the restoration on the lateral surface of the premolar.