The purpose of the presented work is to increase the efficiency of restoring partial defects of crown parts of teeth with onlays by studying the effectiveness of their use through microbiological, experimental mathematical and clinical researches.
To achieve the aim, the work was carried out in three stages, which differed in objects and methods of research.
At the first stage of the work, a bacteriological study of dental plaque and saliva was conducted among 90 participants of the experimental group and 20 of the control group. Thus, 395 unique isolates were obtained (338 from patients with dental caries and 57 from healthy volunteers). According to the obtained results, all samples from all the participants were positive for microbiota
At the second stage of the work, we compared the stress-strain states of the simulation models “tooth – restoration” for the first mandibular molar when using different structural materials: composite, ceramic and zirconium dioxide. Computer simulation models of biomechanical systems were obtained by digital scanning of the first mandibular molar in STEP format
Control was carried out in the form of numerical characteristics and graphic visualization in the EXOCAD program. The finite element method, information technologies and program codes of the ANSYS Workbench 12.1 system were used to perform calculations. After testing the developed discrete models, they were checked for compliance and coincidence of numerical results in fields of high stress gradients using the ANSYS 12.1 software, The maximum values of displacements, gradients and amplitudes of the equivalent stress according to Mises in the structural elements of each of the three biomechanical systems “tooth – restoration” were subject to analysis. The stress values were derived using the method of linear scaling of the data of the numerical solution of boundary value problems of the theory of elasticity for small deformation values at a functional force load of the first mandibular molar of 100 N. The values of the safety factor of the structural elements of biomechanical systems were calculated as the ratio of the values of the ultimate strength to the maximum values of the equivalent Mises stress, scaled by a factor of 10 for a force load of 100 N. It was found that immediately after the treatment, all the performed restorations met the requirements according to all criteria. While after 12 months, 95.8 % of direct composite restorations, 97.0 % of metal-ceramic and 100 % of zirconia restorations were successful. The reason for the unsuccessful composite restorations in all cases was excessive wear of the occlusal surface. For metal-ceramic onlays, the problem of ineffective restorative treatment was the disorders of the marginal fit. Therefore, it is possible to achieve effective restoration of partial defects of distal teeth using both direct composite restorations and indirect metal-ceramic and zirconium restorations. However, the greatest efficiency by criteria of the quality of restorations, the state of periodontal tissues, and the occlusion is demonstrated by zirconium dioxide onlays, manufactured using CAD/CAM technology
