Osteogenic effects of bioabsorbable magnesium implant in rat mandibles and in vitro

Bone augmentation or grafting is often required for placement of dental implants or surgical reconstruction of bony defects. Bioabsorbable magnesium implant was shown to promote osteogenesis in long bones. The objectives of this study were to determine osteogenic effects of pure magnesium (Mg) in rat mandible and underlying mechanisms.

Pure Mg was implanted in sockets after rat mandibular incisors were extracted. Titanium (Ti) was used as control. Systemic effects were determined by serum Mg level and histologic analyses of liver and kidney. Local Mg concentration was measured by microscopy-energy-dispersive spectroscopy (SEM-EDS). Alveolar bone was analyzed by micro-computed tomography (micro-CT) and histology. Osteogenic effects of 0.8 to 20 mM magnesium chloride (MgCl₂ ) on periosteum-derived cells (PDCs) were evaluated by proliferation, alizarin red staining and quantitative RT-PCR assays.

Systemic effects were similar in Mg and Ti groups. Higher local Mg concentration was detected in Mg group (P < 0.05). Micro-CT showed higher alveolar bone volume (2- and 6-weeks post-operation) and denser cancellous bone (2 weeks post-operation) in Mg group, with significant amount of new subperiosteal bone formation on lateral alveolar bone surfaces by H&E staining. In PDC culture, proliferation rates, osteogenic gene expression for runt related transcription factor 2 (Runx2), bone sialoprotein (Bsp) and osteocalcin (Ocn), as well as calcium nodule formation rose significantly in 5, 10, and 20 mM MgCl₂ groups.

Rapid osteogenesis (especially subperiosteal) is induced by pure Mg in rat mandibular alveolar bone. Osteogenic capacity of PDCs is enhanced by higher Mg ion concentrations in vitro.