A mouse model of mandibular osteotomy healing.

The purpose of this study was to establish a novel mouse model of membranous osteotomy healing. By applying this model to transgenic mice or using in situ hybridization techniques, we can subsequently investigate candidate genes that are believed to be important in membranous osteotomy healing. In the current study, 20 adult male CD-1 mice underwent a full-thickness osteotomy between the second and third molars of the right hemimandible using a 3-mm diamond disc and copious irrigation. Compo-Post pins were secured into the mandible, 2 mm anterior and posterior to the osteotomy. After the soft tissues were reapproximated and the skin was closed, an acrylic external fixator was attached to the exposed posts for stabilization. The animals were killed on postoperative day number 7, 10, 14, and 28 (n=5 animals per time point). The right hemimandibles were decalcified and embedded in paraffin for histologic evaluation or immunohistochemistry localizing osteocalcin. At 7 days after the osteotomy, early intramembranous bone formation could be seen extending from either edge of the osteotomized bone. By 10 days, an increasing number of small blood vessels could be seen within and around the osteotomy. At 14 days, the bone edges were in close approximation, and by 28 days the callus had been replaced by actively remodeling woven bone in all specimens examined. Immunohistochemistry demonstrated that osteocalcin expression correlated temporally with the transition from a soft to a hard callus. Furthermore, osteocalcin was spatially confined to osteoblasts actively laying down new osteoid or remodeling bone. This study describes a novel mouse model of membranous osteotomy healing that can be used as a paradigm for future osteotomy healing studies investigating candidate genes critical for osteogenesis and successful bone repair.