Facial skeletal growth in growing "toothless" osteopetrotic (op/op) mice: Radiographic findings

The defective bone resorption in the osteopetrotic (op/op) mouse brings abo ut failure of tooth eruption. Furthermore, the op/op mouse has been studied as a "toothless" mouse in recent morphological and physiological investiga tions of the relationship between mastication and masseter muscle developme nt. The present study was conducted to examine in detail the nasal bone and the premaxillary bone in this mutant mouse and to assess the roles of inci sor growth and the mechanical stress of mastication in nasal bone and prema xillary bone growth. The forms of the nasal bone and the premaxillary bone were observed using roentgenography in both toothless op/op, and normal (co ntrol) mice. In the op/op mouse, the nasal bone and the premaxillary bone s how remarkable deformity. In contrast, the normal mouse appears well develo ped. This suggests that growth of the incisor root is important to normal u pper jaw growth in the mouse. Furthermore, it is proposed that the upper fa cial phenotype seen in the op/op mice results from not only decreased bone resorption. but also from absence of the mechanical stress provided by norm al mastication.