EXPRESSION OF ADHESION MOLECULES DURING TOOTH RESORPTION IN FELINE TEETH - A MODEL SYSTEM FOR AGGRESSIVE OSTEOCLASTIC ACTIVITY

Tooth resorption, a common feline dental problem, is often initiated a t the cemento-enamel junction and hence is called cat 'neck' lesion. S tudies have demonstrated that osteoclasts/odontoclasts are increased a nd activated at resorption sites, and that areas of resorption are par tly repaired by formation of tissues resembling bone, cementum, and po ssibly dentin. However, the cellular/molecular mechanisms/factors invo lved in resorption and repair are unknown. In this study of tissues fr om cats with 'neck' lesions, we used specific antibodies and immunohis tochemical analyses to examine adhesion molecules associated with mine ralized tissues, bone sialoprotein (BSP) and osteopontin (OPN), and a cell-surface receptor linked with these molecules, alpha(v) beta(3), f or their localization in these lesions. In addition, to determine gene ral cellular activity during repair, we performed in situ hybridizatio n using a type I collagen riboprobe. Results showed OPN localized to r esorption fronts and reversal lines, while BSP was localized to revers al lines. However, some osteoclasts and odontoblasts ''sat'' on minera lized surfaces not associated with OPN. The cell-surface receptor, alp ha(v) beta(3), was localized to surfaces of osteoclasts/odontoclasts. Type I collagen mRNA was expressed where osteoblasts attempted to repa ir mineralized tissue. In contrast, odontoblasts did not express mRNA for type I collagen. This study suggests that osteoclastic resorption is the predominant activity in 'neck' lesions and that this activity w as accompanied, at least in part, by increased concentrations of OPN a nd an associated integrin, alpha(v) beta(3), at resorption sites. Lack of collagen expression by odontoblasts indicates that odontoblasts do not play an active role in attempts at repair.