Immunodetection of Osteopontin at Sites of Resorption in the Pulp of Rat Molars

Osteopontin (OPN) has been proposed to act as a substrate for osteoclast adhesion during bone resorption. The aim of the present study was to examine the presence and distribution of OPN at sites of resorption in traumatized radicular pulp. The upper first molars of 6-week-old male Sprague-Dawley rats were luxated and then repositioned in the original sockets. The animals were sacrificed by intracardiac perfusion at 10 and 14 days after tooth reimplantation. The teeth were decalcified in EDTA and then processed for embedding in paraffin for histochemistry or LR White resin for immunocytochemistry. Odontoclasts were identified by their multinucleated morphology and expression of tartrate-resistant acid phosphatase (TRAP). Osteopontin was immunolocalized using postem-bedding colloidal gold labeling with a chicken egg yolk anti-rat OPN antibody. After reimplantation of the teeth, TRAP-positive cells were present along the pulp dentin wall. Osteopontin was not consistently detected at exposed predentin/dentin surfaces. However, gold particles were often found at the margin of resorption lacunae. Labeling was also seen over the Golgi region and cytoplasmic vesicles of odontoclasts and of neutrophils and fibroblast-like cells. The results suggest that accumulation of OPN at the predentin/dentin surface is not a prerequisite for adhesion of odontoclasts to the wall substance and that recruited odontoclasts produce OPN locally to mediate cell and/or matrix events within the resorption lacuna.