3D finite element analysis of the dental implant loss effect on the stress distribution in the mandibular implant-supported prosthesis

An implant-supported prosthesis may have as few as three supporting implants, and the loss of one of them may lead to the loss of the entire structure. The framework of the Trefoil design is a standard bar made of high-strength titanium. Cyclic loading of metals and metal structures brings about the effect reducing the strength characteristics and known as fatigue. Fatigue limit is the value of stress below which the cyclic loading cannot destroy the structure. The aim of the work is to determine the treatment tactics for a patient having lost a distal implant and justify it according to the results of a three-dimensional finite element analysis of the effect of one dental implant loss on the biomechanics of a mandibular implant-supported prosthesis with three supports. Bridge loading modeling was carried out with the Ansys 19.3 finite element analysis package and thus the stress-strain condition of the prosthesis and its components, implants and the frame itself, namely the bar, were determined. The stress values obtained allowed to draw the conclusion about the condition of metal structures under cyclic loading. The geometric model represents the mandible, including the compact and spongy bone layers, a bridge structure with two implants screwed into the spongy layer, and artificial teeth attached to the implant structure. The model was created with the use of a real patient’s computerized cone-beam tomogram (CBCT) findings. The finite element model consists of 383 507 second-order tetrahedral elements and 619 339 nodes. The components are interconnected by contact elements of the "bonded" type, imitating a rigid connection without slipping. With 220 MPa being the fatigue limit for the loaded titanium implant construction, it was concluded that extended prosthesis construction can withstand an unlimited number of loading cycles at 100 N loading with the maximum stress of 154 MPa occurring in the left part of the jaw. The clinician’s tactics was determined for the potential loss of function or removal of one of the three Trefoil supporting implants: the prosthesis must not be removed until reimplantation.