Results of stress-strain states study in prosthetics of different types of atrophy of edentulous mandible

Complete dentures remain still popular due to the economic component of such prosthetic treatment. However, additional fixation on intraosseous implants provides a greater clinical and functional effectiveness and a greater level of satisfaction with the results of prosthetics in edentulous patients. At the moment, the biomechanical aspects of complete denture prosthetics and prosthetics with fixation on implants, taking into account the degree of atrophy of the edentulous jaws, are not complete understood. Such studies make it possible to create recommendations on the choice of prosthetic tactics for edentulous patients. The aim of the research was to study the distribution of stress-strain states in prosthetics of the edentulous mandible with complete dentures and with designs supported on intraosseous implants, taking into account the type of atrophy. It was carried out computer simulation of 8 virtual finite element models of mandible with different types of atrophy. According to Keller they were 4 models: of the biomechanical system simulation "complete denture – mandible" and 4 ones – "denture – intraosseous implants – mandible". In each of the models, a chewing load of 100 N was simulated (symmetrically and asymmetrically). The ANSIS 12.1 finite element analysis was used to calculate the stress-strain states in the described calculation systems. It was estimated the distribution of stresses in cortical bone and displacements of the dentures on the prosthetic bed. Under using complete dentures, the maximum stresses in the bone tissue of the prosthetic bed were observed for the third type of mandible atrophy with all types of power load, the smallest ones – for the fourth type. Additional fixation of removable dentures in simulation models of biomechanical systems “denture – intraosseous implants – mandible” lead to a significant increase in stresses in the alveolar bone. The maximum stresses were observed in the area of the marginal bone, while their greatest values were in the well-expressed alveolar part of the mandible for first and third types by Keller. The movements of bases of complete dentures were insignificant and fluctuated within hundredths of a millimeter for all types of atrophy. The use of intraosseous implants for fixation of dentures caused increase in movements by several times. Besides, displacement fields were characteristic: they were uniform for complete dentures but in the use of implants – not. The expressed alveolar process in the first and third types of atrophy of the edentulous mandible caused an increase in the displacements of the distal sections of the dentures on both sides with a symmetrical force load and on one side – with an asymmetric one. It can be assumed that such a distribution of stress-strain states accelerates atrophy of prosthetic bed tissues. As a result of prosthetics of complete defects of lower dentitions, both with traditional complete dentures and with additional support on implants, different distribution of stress-strain states occurs in different phases of the chewing act in the bone of the prosthetic bed, the character of which is determined by the shape of the alveolar part described by Keller's classification. The results allow us to develop an algorithm for determining the kind of prosthetics for edentulous patients, depending on the type of mandible atrophy.