Stress-strain state of dental immediate prosthesis and associated tissue under the influence of external force

Purpose: to analyze the stress-strain state (SSS) of a removable plate immediate denture with a printed dentition made of polymethyl methacrylate (PMMA) and a polyethylene terephthalate (PET) base under multifactor loading conditions based on the principles of mathematical modeling. Materials and methods: For mathematical modeling of SSS, Comsol Multiphysics 5.6 software (Comsol Inc., USA) was used, which provided numerical data for analytical interpretation. We considered a flat 2D model consisting of a printed monolithic dentition and a PMMA bonding layer, a PET base, the mucous membrane of the prosthetic field and jaw bone tissue. Results: The fields of von Mises stresses (VM) and deformations under the influence of normal, oblique and tangential loads (up to 500 N), the localization of their maximum values and the average value inside the prosthetic structure, mucous membrane and bone tissue were determined. The maximum values of VM in the mucous membrane are compared with the pain threshold based on known literature data on algesiometry of the oral mucosa. An assessment was made of the critical length of microcracks (CLM) according to Griffiths, which lead to the formation of a main crack followed by brittle fracture of the structure base. Using the phase field method, the probability of crack formation in the considered model of an orthopedic structure under the influence of static loads of various magnitudes and directions was calculated. Conclusions: Using the method of mathematical modeling of SSS, it was shown that failures when using immediate dentures with printed teeth made of PMMA and a PET base can be caused by the effect of overloading the areas of the base and caused by the deformation process inside the prosthetic structure. The maximum stress in the prosthetic elements was 79.7 MPa and deformation – 0.47 mm. The pain threshold of the oral mucosa is higher than the highest stress value in the prosthetic bed according to Mises (0.002 MPa) for normal load of 500 N. The SSS heterogeneity coefficient of the removable plate immediate prosthesis model is 8.6. The critical length of a microcrack according to Griffiths is lcrit = 1.9...2.7 µm. Using the Comsol Multiphysics phase field method, it was established that the probability of the formation of a large crack in the base of the prosthesis was 6·10–3 %, 0.36 %,0.73 % for a normal, inclined and shear load of 500 N, which is a sufficient value for the operation of removable laminar dentures with printed teeth from PMMA and a PET base during the warranty period.