Evaluation of Bone Quality in Mandible of Young M-CSF Deficient-Induced Osteopetrotic Mouse

摘要

The preferred crystallographic orientation of the biological apatite (BAp) c-axis has been shown to be one of the important bone quality indices that sensitively reflect in vivo stress distribution and dominate bone mechanical functions. The BAp orientation is expected to be regulated by bone modeling or remodeling by osteoblasts and osteoclasts whose primary functions are bone formation and absorption, respectively. Mouse with macrophage colony-stimulating factor (M-CSF) deficiency-induced osteopetrosis (op/op mouse) is a suitable animal model to elucidate the role of osteoclasts in the development of BAp orientation. In this study, the mandibles of 5-week-old mice were used because their mandible is subjected to complicated stresses including a biting stress locally applied just around the roots of the teeth and a bending stress applied along the mesiodistal axis of the mandibular body, and the response to the stress distribution is important to the formation of BAp orientation. The normal mouse mandible (control) has a one-dimension preferred BAp orientation in the mesiodistal direction, but just near the tooth root, the direction of BAp orientation changes locally to that of the tooth root responding to a biting stress. In the op/op mouse, the preferred BAp orientation only along the mesiodistal direction is found, but the degree is quite lower than that in normal mice. Moreover, the effect of biting was not observed in op/op mice because these mice are devoid of teeth eruption and are unable to bite. This suggests that M-CSF plays a critical role in forming the optimal BAp orientation, and therefore, the op/op mouse without osteoclasts cannot fully develop the appropriate bone microstructure in response to in vivo stress distribution, although BAp orientation is very sensitive to local in vivo stresses in normal animals with normal osteoclast function.