*3.2. Stress and Strain in TMJ Implants*

FE simulations resulted in lower stress in anterior part of the condylar and fossa prostheses (see Figures 30 and 32) similar to what found in [20,28] although their FE studies included only the condylar TMJ implants with different loading conditions. The von Mises stress found in condylar and fossa components of both types of implants were lower than the yield strength of their materials Figure 33, Ti-6Al-4V and UHMWPE, respectively. The trends in the stress and strain profiles under normal and over-loading conditions were similar in both types of total TMJ prostheses. von Mises stresses of higher magnitude were developed in condylar neck, posterior part of condylar head, and inferior region of ramal component compared with rest of the condylar/ramus prosthesis. For fossa component, magnitude of von Mises stress and strain was higher in the posterior region on the articulating surface, Figures 33 and 34. *Materials* **2022**, *15*, x FOR PEER REVIEW 30 of 34

**Figure 33.** Peak von Mises stress in the mandibular and fossa bone adjacent to fixation screws of total TMJ prostheses during FE simulations under normal and worst-case/over-load configurations. **Figure 33.** Peak von Mises stress in the mandibular and fossa bone adjacent to fixation screws of total TMJ prostheses during FE simulations under normal and worst-case/over-load configurations.

**Figure 34.** Peak micro-strain in the mandibular and fossa bone adjacent to fixation screws of total TMJ prostheses during FE simulations under normal and worst-case/over-load configurations.

Other than where the actual loads and constraints were applied, the stress concentration was highest around the inserted screw and the screw holes in the host bone. The medial notches in the condylar and fossa prostheses are designed to provide improved stability by promoting post-implantation bone growth into the perforated surfaces of the notches. Von Mises stress in the notch regions of the condylar and fossa implants were less than that in the screw regions, indicating that the notches may not act as stress risers in the device. Stress profile in the host bone portion where the medical notches of the implant are inserted show stresses lower than that at the screw holes, but higher than

**Figure 34.** Peak micro-strain in the mandibular and fossa bone adjacent to fixation screws of total TMJ prostheses during FE simulations under normal and worst-case/over-load configurations. Other than where the actual loads and constraints were applied, the stress concen-**Figure 34.** Peak micro-strain in the mandibular and fossa bone adjacent to fixation screws of total TMJ prostheses during FE simulations under normal and worst-case/over-load configurations.

**Figure 33.** Peak von Mises stress in the mandibular and fossa bone adjacent to fixation screws of total TMJ prostheses during FE simulations under normal and worst-case/over-load configurations.

tration was highest around the inserted screw and the screw holes in the host bone. The medial notches in the condylar and fossa prostheses are designed to provide improved stability by promoting post-implantation bone growth into the perforated surfaces of the notches. Von Mises stress in the notch regions of the condylar and fossa implants were less than that in the screw regions, indicating that the notches may not act as stress risers in the device. Stress profile in the host bone portion where the medical notches of the implant are inserted show stresses lower than that at the screw holes, but higher than Other than where the actual loads and constraints were applied, the stress concentration was highest around the inserted screw and the screw holes in the host bone. The medial notches in the condylar and fossa prostheses are designed to provide improved stability by promoting post-implantation bone growth into the perforated surfaces of the notches. Von Mises stress in the notch regions of the condylar and fossa implants were less than that in the screw regions, indicating that the notches may not act as stress risers in the device. Stress profile in the host bone portion where the medical notches of the implant are inserted show stresses lower than that at the screw holes, but higher than those in other parts of the host bone. This indicates that the stress developed in the notches under functional loading may augment bone growth into the perforated notches, thereby maximizing the opportunity for improved stability of the prostheses. Also, in all simulations, the peak von Mises stresses in the condylar component were higher than those in the fossa component of the total TMJ prostheses (see Figure 35). This may have resulted from the model constraints which allowed mobility of the condylar/ramal prosthesis along with natural mandible and kept the artificial fossa fixed in its position along with the host fossa bone.
