Osteoprotegerin and osteoclast differentiation factor in tooth eruption

A critical cellular event in tooth eruption is the formation of osteoclasts that are needed for bone resorption to form an eruption pathway. To analyz e molecular regulation of osteoclast formation and activation, we examined the expression of osteoprotegerin (OPG), an inhibitor of osteoclast formati on. In vivo, the gene expression of OPG is reduced in the dental follicle o f the first mandibular molar of the rat at day 3 post-natally and in the mo use at day 5. This correlates with the days of maximal mononuclear cell inf lux and osteoclast numbers in the rat and mouse. Thus, inhibition of OPG ge ne expression on these days might allow osteoclasts to be formed and/or act ivated. In vitro studies demonstrated that both colony-stimulating factor-1 and parathyroid hormone-related protein reduced OPG gene expression in fol licle cells, suggesting that these are candidate molecules for the in vivo inhibition of OPG expression. Osteoclast differentiation factor (ODF) immun olocalizes to the alveolar bone stromal cells adjacent to the follicle, whe reby it might act to stimulate fusion of the mononuclear cells in the folli cle.