Third-generation modular mandible endoprosthesis in Macaca fascicularis.

The aim of this study was to develop a third-generation modular mandible endoprosthesis that would experience less stress concentration at its stems compared to earlier generations, thereby minimizing micromotion and achieving long-term stability. In this three-piece modular design, different degrees of movement were incorporated between the endoprosthesis module interfaces. It was hypothesized that this unique feature would minimize stress concentration at the stems and hence promote osseointegration during the early phase of implantation. The endoprosthesis system was made of commercially pure grade 4 titanium, machined and surface-treated, then sterilized and implanted in segmental mandible defects of nine Macaca fascicularis. Clinical, radiological, histological, and histomorphometric evaluations were performed 4 months post-implantation. The endoprosthesis systems with a degree of movement incorporated, exhibited superior performance compared to the rigid system: 30.9-34.8 times higher percentage bone-implant contact (P< 0.0001) and 3.4-4.1 times higher percentage bone area (P<0.0001), with osseointegration noted at the posterior stems. However, fibrous tissue encapsulation was noted around the majority of the anterior stems in all groups. Although the degree of movement was favourable for improving bone healing and stability of the endoprosthesis system, more work needs to be done to investigate other strategies to further reduce loading on the endoprosthesis to achieve predictable osseointegration at the stems.