Morphological change of the nasopremaxillary suture in growing "toothless"osteopetrotic (op/op) mice

Osteopetrotic (op/op) mice are known to commonly show a failure of tooth er uption. It is also well understood that masticatory function is highly asso ciated with the craniofacial morphology of the growing mouse, however, the effects on sutural growth have not been studied. The present study was cond ucted to examine, in detail, the morphological and histological changes of the nasopremaxillary suture in these mutant mice and to assess a role of me chanical stress from mastication in the sutural growth. The width of the na sopremaxillary suture was measured on the section for the superior (PI), mi ddle (P2), and inferior (P3) levels. The width of the nasopremaxillary sutu re for the P1 level in the normal mice fed a solid diet was significantly s maller in 30-day-old mice than in 15-day-old mice, whereas the width for th e level P3 was significantly greater in the 30-day-old mice than in the 15- day-old mice. These changes in the sutural space were more prominent in the normal mice fed a solid diet than in the normal mice fed a granular diet. The sutural widths for all the levels became smaller in the 30-day-old op/o p mice than in the 10-day-old op/op mice. The endocranial area of the nasop remaxillary suture showed synostosis in 30-day-old op/op mice. Tn both the normal and op/op mice, the number of tartrate-resistant acid phosphatase (T RAP)-positive cells was greatest at the age of 15 days. Moreover, the TRAP- positive cell number was smaller in the op/op mice than in the normal mice for all the experimental stages. Since, in general, mastication begins in m ice after tooth eruption, i.e. from 15 to 30 days after birth, the present findings suggest that failure of tooth eruption and the reduced masticatory function restrict sutural modification.