Metformin-Incorporated Gelatin/Nano-Hydroxyapatite Scaffolds Promotes Bone Regeneration in Critical Size Rat Alveolar Bone Defect Model.

In this study, we fabricated gelatin/nano-hydroxyapatite/metformin scaffold (GHMS) and compared its effectiveness in bone regeneration with extraction-only, Sinbone, and Bio-Oss Collagen® groups in a critical size rat alveolar bone defect model. GHMS was synthesized by co-precipitating calcium hydroxide and orthophosphoric acid within gelatin solution, incorporating metformin, and cross-linked by microbial transglutaminase. The morphology, characterization, and biocompatibility of scaffold were examined. The in vitro effects of GHMS on osteogenic gene and protein expressions were evaluated. In vivo bone formation was assessed in a critical size rat alveolar bone defect model with micro-computed tomography and histological examination by comparing GHMS with extraction-only, Sinbone, and Bio-Oss Collagen®. The synthesized GHMS had a highly interconnected porous structure with a mean pore size of 81.85 ± 13.8 µm. GHMS exhibited good biocompatibility; promoted ALPL, RUNX2, SP7, BGLAP, SPARC and Col1a1 gene expressions; and upregulated the synthesis of osteogenic proteins, including osteonectin, osteocalcin, and collagen type I. In critical size rat alveolar bone defects, GHMS showed superior bone regeneration compared to extraction-only, Sinbone, and Bio-Oss Collagen® groups as manifested by greater alveolar ridge preservation, while more bone formation with a lower percentage of connective tissue and residual scaffold at the defect sites grafted with GHMS in histological staining. The GHMS presented in this study may be used as a potential bone substitute to regenerate alveolar bone. The good biocompatibility, relatively fast degradation, interconnected pores allowing vascularization, and higher bioactivity properties of the components of the GHMS (gelatin, nHA, and metformin) may contribute to direct osteogenesis.

Decoronation-induced infected alveolar socket defect rat model for ridge preservation.

Current rat alveolar ridge preservation models have not been well standardized. In this study, we proposed decoronation-induced infected alveolar socket model of rat. The bilateral maxillary first molars (M1) of twenty-four rats were decoronized or extracted. After 2, 6, 10, and 14 weeks, bone and soft tissue changes at M1 and periodontal conditions of maxillary second (M2) and third molars (M3) were evaluated by micro-computed tomography and histological analysis. Additional eighteen rats with standardized size defects were grafted with Bio-Oss Collagen to compare with unmanipulated contralateral side. Decoronation preserved greater bone and soft tissue dimensions at M1, provided larger three-dimensional (3D) bone contour volume, but also promoted periodontal breakdown of M2 Histological results showed intense inflammatory cell infiltrations and severe bone resorption within M1 socket and at mesial aspect of M2. The critical dimensions to accommodate largest standardized defect at M1 were 2.2-2.3 mm at vertical bone height and 2.8-3.2 mm at alveolar crestal width. Bio-Oss Collagen could not fully preserve buccal or palatal bone height but could be beneficial in preserving ridge width in large alveolar defects. Collectively, if periodontally-involved alveolar bone defect is preferred, we suggest extracting M1 roots 6 weeks after decoronation to allow periodontitis to occur at M2. If standardized critical dimension defect is preferred, we suggest extracting M1 roots 2 weeks after decoronation, and creating defect in the middle of M1 site with size no larger than 2.7 mm diameter to its full depth.