The dissertation presents a theoretical basis and practical solution to the actual problem of dentistry and maxillofacial surgery - improving the efficacy of surgical treatment and rehabilitation of patients with fractures of the condylar head (CHF) of the mandible by developing new methods of osteosynthesis using CAD / CAM technology and patient-specific fixators.
The research was aimed at analyzing the topographic characteristics of CHF, determining biomechanically unfavorable types of fractures, creating new systems for their open reduction and fixation, as well as at development of biomechanically-based approaches to surgical treatment of CHF using CAD / CAM technologies and patient-specific fixators.
The research program consisted of 2 stages: experimental and clinical. At the first stage, the general principles of the biomechanical behavior of the “fixator-bone” systems in CHF were studied, as well as the rigidity and strength of different types of fixators in variable deformation conditions. Thus, in experiment on dry human cadaver mandibles, a comparison of traditional fixation systems used in osteosynthesis of the mandibular head (titanium screws, bioresorptive pins and T-shaped plates) was performed. A distinctive feature of the research was the reproduction of different types of deformation, which corresponded to the real conditions of the mandibular load in the relevant phases of the masticatory cycle. Subsequently, using the method of simulation computer modeling, the elements of fixing structures were improved and their biomechanical characteristics in a complex stress-strain state were studied.
The data obtained in the experiment formed the basis for the development of the new approaches to the treatment of CHF with the use of computer methods of diagnosis, planning and implementation of surgical interventions in accordance to a complete digital protocol. The efficacy of the developed approaches was studied in a prospective controlled study conducted in 42 patients with 50 CHF.
In the experimental studies, it was found out that traditional titanium bicortical screws provide the highest rigidity and strength of fixation under the load in the sagittal and frontal planes: 46.9 ± 31.37 and 36.92 ± 20.34 N / mm, respectively. Fixation with bioresorptive pins showed less rigidity at both sagittal (29.07 ± 9.03 N / mm) and frontal load (39.3 ± 16.6 N / mm). The lowest rigidity was found when fixing the fragments of the mandibular head with a T-shaped titanium miniplate: 10.9 ± 10 N / mm - in sagittal and 17.9 ± 10.11 N / mm – in frontal loading. Fixation with one screw or pin, regardless of the material used, was not resistant to torsional deformation. Instead, the torsional rigidity of the T-plates was quite high and averaged 518.3 ± 111.9 N * mm / Rad. In real clinical conditions, torsion can be effectively compensated by fracture surface irregularities and friction force between fragments only in biomechanically favorable cases; otherwise, to stabilize this type of deformation, it is advisable to use a combination of bicortical positioning screws with mini- and microplates.
Subsequently, the methods of 3D-visualization and computer simulation were used to study the topographic and anatomical features of different types of CHF and new anatomical and functional concept of design, manufacturing and usage of the surgical guides and patient-specific fixators in treatment of this category of patients, based on digital protocol was proposed.
