MATHEMATICAL SUBSTANTIATION OF THE USE OF DIFFERENT TYPES OF CLAMMERS DURING THE RESTORATION OF THE DENTITION WITH DOUBLE-SIDED DISTAL DEFECTS AND THE DEFECT INCLUDED IN THE FRONTAL AREA BY REMOVABLE PROSTHETICS
The basic conditions that ensure good functional qualities and durability of prosthetic structures from the point of view of biomechanics, undoubtedly include an optimal way of fixing a partial removable prosthesis, which consists in the correct choice of the clamping system that ensures reliable fixation of the prosthesis in the given position and at the same time causing a minimum of harm supporting teeth, as well as the most rational distribution of occlusal loads transmitted to the supporting tissues, since it is these factors that determine the durability functioning dentures. The purpose of biomechanical studies is to analyze the stress-strain state of the supporting teeth of partial removable prostheses replacing the included and terminal defects of the dentition when fixing the prosthesis on the supporting teeth with the help of holding and supporting-retaining clamps. The studies were performed on a model of the mandible with overall dimensions of the cross section corresponding to some average dimensions. The first volumetric finite element model was developed to study the stress-strain state of periodontal ligaments of supporting teeth and supporting gingival tissues when the incomplete and bilaterial end defects of the dentition were replaced (1 class 1 subclass by Kennedy) of the mandible by a removable denture with fixation by retaining clamps on the canines and the first premolars. The second volumetric finite element model is designed to study the stress-strain state of periodontal ligaments of supporting teeth and supporting gum tissues when the included and two-sided end defects of the dentition of the lower jaw are replaced by a removable clasp prosthesis with fixation of support-retaining clamps on canines and first premolars with support arms of clamps from the distal sides of premolars. As a result of the studies performed, the following conclusions can be drawn: In both considered variants fixation of removable clasp prostheses loaded with maximum values of equivalent stresses in the periodontium of the supporting teeth is localized at the apex of the alveolar ridge, which indicates the transfer of the "clutching" supporting teeth of the clasp prosthesis. The maximum values f equivalent stresses in the periodontitis of the supporting teeth during fixation of the removable clasp prosthesis by the support-retaining clamps on the canines and the first premolars exceed the corresponding values of the equivalent stresses for the case of fixing the prosthesis with retention clamps by 30-140%! With an increase in gum compliance, the values of equivalent stresses in the periodontitis of the supporting teeth during fixation of the removable clasp prosthesis by the retaining clasps vary insignificantly within 25%, and an increase in the corresponding equivalent stresses with the use of support-holding clasps may be 65%. In order to ensure the maximum sparing regimen of periodontal tissues of supporting teeth and as a result - the possibility of the most prolonged use of the prosthesis without loosening of the supporting teeth, it seems more expedient to give preference to the use of clasp prostheses with the fixation of the retaining clasps.
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