Stress Analysis of the Mandibular Premolar Teeth in Molarless Patients

Objectives: Loss of molar teeth can alter the mechanical environment in adjacent premolar teeth. The purpose was to investigate the stress distributions around the premolar teeth in patients with missing molar teeth. Methods: Seven subjects with loss of right mandibular molar teeth restored with removable dentures and seven controls with complete dentition were included. All subjects were female and aged between 51 and 67. Finite element model of the first and second premolar teeth, periodontal ligament (PDL) and bone was constructed for each patient by means of radiographs and study models. Alveolar bone level was indexed on radiographs. Bite force under the maximum clenching was registered with and without denture wearing (Dental Prescale System, GC). The forces were directed on corresponding occlusal contact locations in the models. Loads registered on denture teeth multiplied by 0.2 were directed on the occlusal rest position. Models were fixed on the lower, mesial and distal surfaces of the bone. Results: In the premolar teeth of all subjects, the maximum principal compressive stress in the cancellous bone near the root apex was proportional to the bite force, but inversely proportional to the alveolar support. In the molarless subjects, average bite force and the maximum stress in the cancellous bone slightly but significantly reduced by denture wearing (p<.05), while the maximum principal tensile stresses in the cervical PDL and the cortical bone were not significantly affected by denture wearing. The maximum tensile stress in root surface ranged widely from 11 MPa to 141 MPa in all subjects. Conclusions: The results suggests that the denture wearing on missing molar region reduces the loads on the premolar teeth and the stress at their root apexes; however, this does not necessarily occur in the cervical PDL and the cortical bone.