Objective: To explore the relationship between bone resorption and matrix metalloproteinase-9 (MMP-9) expression in autogenous and allogenic bone grafts.
Materials and methods: A total of 18 critical-size (10 x 15 mm) defects were created in rabbit mandibles bilaterally. Three groups of six defects each were grafted with autogenous endochondral (EC) bone, autogenous intramembranous (IM) bone, and allogenic IM bone. Three months later, the defects were retrieved for quantitative analysis on the basis of histology, immunohistochemistry, and in situ hybridization.
Results: A close relationship existed between MMP-9 expression and graft bone resorption. The parallel between MMP-9 expression and graft bone resorption suggested that bone resorption was accomplished in part by increased MMP-9 production evident in preosteoclasts and osteoclasts.
Conclusions: MMP-9 plays an important role in graft bone resorption. Autogenous EC bone grafts express higher levels of MMP-9 leading to more resorption than autogenous or allogenic IM bone grafts.