In vitro and in vivo evaluation of micro-alloyed magnesium for potential application in alveolar bone fixation screws

Alveolar bone augmentation with fixation screws has difficulties such as non-degradable materials that could lead to secondary surgery and insufficient osseointegration due to the subgingival environment in dental practice. With degradability and a high degree of osteogenesis, Mg alloy is a successful biodegradable material for orthopedic applications, and its application in dentistry has made certain progress. However, considering the unique subgingival healing properties of oral implants, there is still a gap between the desired material properties for clinical applications and available materials. Indeed, studies on the use of Mg-based fixation screws for dentistry applications are still rare. In this study, we reported a magnesium alloy with low combined addition of strontium and lanthanum. The mechanical properties, degradation behavior, osteogenesis, and gingival compatibility were systematically investigated for assessing its potential application in alveolar bone fixation screws. With the alloying element content restricted to 0.3 wt.%, Mg-Sr-La alloy still exhibited good mechanical properties, with yield tensile and compressive strength twice higher than those of pure Mg. The in vitro degradation rate of this alloy was 0.10 mm y^–1, which was slightly slower than high-purity Mg. The indirect and direct cell assay confirmed the elevated osteoblastic differentiation of MC3T3-E1 and migration of HGF-1 cells. Moreover, Mg-Sr-La alloy demonstrated a relatively slow degradation in the maxillary bone of Beagles. A remarkable promotion of the bone-implant contacts and significantly decreased fibrous encapsulation was observed in the subgingival environment, implying superior osseointegration of the experimental alloy than the titanium control. The empirical findings here reveal the great potential of Mg-Sr-La alloy for the application in alveolar bone fixation devices.