Numerical and experimental study of premolars strength properties with pin zirconium inserts at different load angles

To study the physical and mechanical properties of zirconium dioxide post stump structures made by computer modeling and milling (CAD/CAM), the stress-strain state and their strength characteristics, numerical and experimental studies were carried out. The test specimens were a system consisting of previously extracted premolar teeth with an absent anatomical crown, a prepared root canal and a post stump inlay fixed in it, an artificial zirconium dioxide crown fixed on the pin insert, and a part of the root. The prepared teeth for the placement of the posts were scanned in the dental laboratory, after which the pin insert of zirconium dioxide were milled. Investigated 2 groups of samples: specimens of the first group were processed in a sandblasting unit; the specimens of the second were not subjected to any mechanical and temperature treatment. To test the compressive strength of the specimens, we used an Instron 5982 universal floor electromechanical testing machine in static mode under conditions of a single increasing load. The specimens were tested with vertical load and at an angle of 15° with and without sandblasting with aluminum oxide powder. The value of the force for each variant was obtained, at which the samples were destroyed. Also, a numerical study was carried out by the finite element method on the developed mathematical model of the stress-strain state dependence of the sample on the applied functional load acting vertically on the occlusal surface of the tooth and at an angle of 15°. The problem was considered in an axisymmetric setting. The computer model included a premolar tooth with a crown, a root and a pin insert, taking into account the mechanical properties of the materials of each of these elements. With an increase in the angle of the load acting on the crown from 0° to 15°, the destruction of the sample occurs at its lower values, by about 10-12 %; the maximum values of stresses were determined in the upper part of the crown and the neck of the tooth (connection of the crown to the root) - in the experiments, destruction occurred precisely in these places. Comparison of the experimental averaged values of the loads at which the destruction of the samples occurs with the numerical values showed their good agreement.