Titanium vs PEO Surface-Modified Magnesium Plate Fixation in a Mandible Bone Healing Model in Sheep.

ABSTRACT

Titanium plates are the current gold standard for fracture fixation of the mandible. Magnesium alloys such as WE43 are suitable biodegradable alternatives due to their high biocompatibility and elasticity modulus close to those of cortical bone. By surface modification, the reagibility of magnesium and thus hydrogen gas accumulation per time are further reduced, bringing plate fixation with magnesium closer to clinical application. This study aimed to compare bone healing in a monocortical mandibular fracture model in sheep with a human-standard size, magnesium-based, plasma electrolytic-oxidation (PEO) surface modified miniplate fixation system following 4 and 12 weeks. Bone healing was analyzed using micro-computed tomography and histological analysis with Movat's pentachrome and Giemsa staining. For evaluation of the tissue's osteogenic activity, polychrome fluorescent labeling was performed, and vascularization was analyzed using immunohistochemical staining for alpha-smooth muscle actin. Bone density and bone mineralization did not differ significantly between titanium and magnesium (BV/TV T1 8.74 ± 2.30%, M1 6.83 ± 2.89%, p = 0.589 and T2 71.99 ± 3.13%, M2 68.58 ± 3.74%, p = 0.394; MinB T1 26.16 ± 9.21%, M1 22.15 ± 7.99%, p = 0.818 and T2 77.56 ± 3.61%, M2 79.06 ± 4.46%, p = 0.699). After 12 weeks, minor differences were observed regarding bone microstructure, osteogenic activity, and vascularization. There was significance with regard to bone microstructure (TrTh T2 0.08 ± 0.01 mm, M2 0.06 ± 0.01 mm; p = 0.041). Nevertheless, these differences did not interfere with bone healing. In this study, adequate bone healing was observed in both groups. Only after 12 weeks were some differences detected with larger trabecular spacing and more vessel density in magnesium vs titanium plates. However, a longer observational time with full resorption of the implants should be targeted in future investigations.