**3. Results**

The von Mises stress and micro-strain in the TMJ prostheses (fossa and condylar), screws, and native bone in regions adjacent to screws were measured. Figures 29 and 30 show visuals of stress profiles in the anatomical components and simple TMJ prostheses, respectively. Figures 31 and 32 show visuals of stress profiles in the corresponding anatomical components and 'notched' TMJ prostheses, respectively. Table 4 summarizes peak von Mises stress occurred in prosthetic components and screws. Peak von Mises stress and strain developed in host bone surrounding the fixation screws of simple and notched TMJ prostheses under normal and worst-case/over-loading configuration are summarized in Table 5.

*Materials* **2022**, *15*, x FOR PEER REVIEW 27 of 34

**Figure 29.** Stress distribution in the host bone components during FE simulations of the total TMJ replacement with custom designed simple TMJ prostheses. (**A**,**B**) Show von Mises stress in the fossa bone under normal and worst-case/over–load configurations, respectively. (**C**,**D**) Show von Mises stress in the mandibular bone under normal and worst-case/over–load configurations, respectively. **Figure 29.** Stress distribution in the host bone components during FE simulations of the total TMJ replacement with custom designed simple TMJ prostheses. (**A**,**B**) Show von Mises stress in the fossa bone under normal and worst-case/over–load configurations, respectively. (**C**,**D**) Show von Mises stress in the mandibular bone under normal and worst-case/over–load configurations, respectively. **Figure 29.** Stress distribution in the host bone components during FE simulations of the total TMJ replacement with custom designed simple TMJ prostheses. (**A**,**B**) Show von Mises stress in the fossa bone under normal and worst-case/over–load configurations, respectively. (**C**,**D**) Show von Mises stress in the mandibular bone under normal and worst-case/over–load configurations, respectively.

**Figure 30.** Peak von Mises stress in patient-specific 'simple' TMJ prosthesis (without notches) during **Figure 30.** FE simulations of two different loading scenarios. ( Peak von Mises stress in patient-specific 'simple' TMJ prosthesis (without notches) during **A**,**B**) Show von Mises total TMJ prosthesis under FE simulations of two different loading scenarios. (**A**,**B**) Show von Mises total TMJ prosthesis under normal loading configuration. (**C**,**D**) Show von Mises stress profile in the prosthesis during FE simulation of worst-case/over-loading scenario.

FE simulations of two different loading scenarios. (**A**,**B**) Show von Mises total TMJ prosthesis under

ulation of worst-case/over-loading scenario.

**Figure 31.** Stress distribution in the host bone components during FE simulations of the total TMJ replacement with custom designed TMJ prostheses with medial notches. (**A**,**B**) Show von Mises stress in the fossa bone under normal and worst-case/over-load configurations, respectively. (**C**,**D**) Show von Mises stress in the mandibular bone under normal and worst-case/over-load configurations, respectively. **Figure 31.** Stress distribution in the host bone components during FE simulations of the total TMJ replacement with custom designed TMJ prostheses with medial notches. (**A**,**B**) Show von Mises stress in the fossa bone under normal and worst-case/over-load configurations, respectively. (**C**,**D**) Show von Mises stress in the mandibular bone under normal and worst-case/over-load configurations, respectively. *Materials* **2022**, *15*, x FOR PEER REVIEW 29 of 34

normal loading configuration. (**C**,**D**) Show von Mises stress profile in the prosthesis during FE sim-

**Figure 32.** Peak von Mises stress in patient-specific 'notched' TMJ prosthesis (with medial notches) during FE simulations of two different loading scenarios. (**A**,**B**) Show von Mises total TMJ prosthesis under normal loading configuration. (**C**,**D**) Show von Mises stress profile in the prosthesis during FE simulation of worst-case/over-loading scenario. *3.1. Stress and Strain in Native Bone*  **Figure 32.** Peak von Mises stress in patient-specific 'notched' TMJ prosthesis (with medial notches) during FE simulations of two different loading scenarios. (**A**,**B**) Show von Mises total TMJ prosthesis under normal loading configuration. (**C**,**D**) Show von Mises stress profile in the prosthesis during FE simulation of worst-case/over-loading scenario.

Small difference in the stress and micro-strain occurred in the host bone adjacent to screws in condylar and fossa components of both total TMJ prosthesis systems. For both

spectively (see Table 5, Figures 29 and 31). These results are comparable to the findings reported by [31] who studied stress distribution in the screws of a condylar implant and host bone. von Mises strain in the bone surrounding prosthetic screws ranged from 1210 microstrain to 1983 microstrain during normal loading, and from 1564 microstrain to 3586 microstrain during over-loading condition. A strain higher than 4000 microstrain can cause hypotrophy of bone [32]. The highest micro-strain in host bone in this study is below the hypertrophy limit. Moreover, use of more screws at appropriate locations would further lower the chances of higher strains capable of bone formation around the screws.

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

*3.2. Stress and Strain in TMJ Implants* 

region on the articulating surface, Figures 33 and 34.
