A pilot study to investigate the histomorphometric changes of murine maxillary bone around the site of mini-screw insertion in regenerated bone induced by anabolic reagents.

OBJECTIVE: The objective of this study was to investigate the histomorphometric changes around the site of mini-screw insertion in the regenerated bone which was induced by an anabolic-injection method using both anabolic peptide and bone morphogenetic protein 2 (BMP-2). METHODS: Twenty-seven eight-week-old C57BL/6J male mice were used. Some mice received submucosal co-injections of anabolic peptide and BMP-2 just in front of the maxillary first molar. Screw insertion was then performed 4 weeks after injection. All mice underwent a weekly in vivo micro-focal X-ray computed tomography (µCT) analysis before being sacrificed at week 8. The bone formation activity was evaluated using fluorescent labelling in the undecalcified sections. The analyses, including screw insertion, were performed in the frontal plane, in front of the site of screw insertion. RESULTS: Reconstructed µCT images revealed that the co-injection of anabolic reagents could lead to a gradual increase in the bone mineral density (BMD) of the injection-induced thickened bone by week 8. Both radiological and histomorphometric analyses indicated that screw insertion did not have any deleterious effects on either the BMD or the bone formation activity of the induced bone. Furthermore, the injection of anabolic reagents also led to an increase in the BMD of the underlying maxillary bone at the injection site. CONCLUSION: Our histomorphometric analyses suggest that performing such anabolic injection to thicken bone could stimulate bone formation in the basal bone as well as in the induced bone. Similar augmentation of bone formation could be obtained even after subsequent screw insertion at the site of the induced bone.

bmp-2 Gene-Transferred Skeletal Muscles with Needle-Type Electrodes as Efficient and Reliable Biomaterials for Bone Regeneration.

BACKGROUND: Bone morphogenetic protein-2 (bmp-2) has a high potential to induce bone tissue formation in skeletal muscles. We developed a bone induction system in skeletal muscles using the bmp-2 gene through in vivo electroporation. Natural bone tissues with skeletal muscles can be considered potential candidates for biomaterials. However, our previous system using plate-type electrodes did not achieve a 100% success rate in inducing bone tissues in skeletal muscles. In this study, we aimed to enhance the efficiency of bone tissue formation in skeletal muscles by using a non-viral bmp-2 gene expression plasmid vector (pCAGGS-bmp-2) and needle-type electrodes. METHODS: We injected the bmp-2 gene with pCAGGS-bmp-2 into the skeletal muscles of rats' legs and immediately placed needle-type electrodes there. Skeletal tissues were then observed on the 21st day after gene transfer using soft X-ray and histological analyses. RESULTS: The use of needle-type electrodes resulted in a 100% success rate in inducing bone tissues in skeletal muscles. In contrast, the plate-type electrodes only exhibited a 33% success rate. Thus, needle-type electrodes can be more efficient and reliable for transferring the bmp-2 gene to skeletal muscles, making them potential biomaterials for repairing bone defects.