Expression of osteopontin mRNA in odontoclasts during experimental tooth movement

Objectives:Osteopontin (OPN) is considered to play important roles in to promote or regulate the adhesion, attachment, and spreading of osteoclasts to the bone surface during bone resorption. Since osteoclasts and odontoclasts have morphological and functional similarities, OPN may play an important role in root resorption. The present study was to investigate the expression of OPN mRNA in periodontal tissue during experimental tooth movement in mice and examine the expression of OPN mRNA in odontoclasts using in situ hybridization. Methods:Using six-week-old male ICR mice, an elastic module was inserted interproximally between the upper first and second molars on the right side. One, 3, 5, 7, and 14 days after insertion of the elastic, maxillary bones were dissected and fixed with 4% paraformaldehyde. The specimens, decalcified in 20% EDTA, were dehydrated and embedded in paraffin. In situ hybridization using RNA probe was performed on these specimens. Tartrate-resistant acid phosphate staining (TRAP) was also performed. Results:One day and 3 days after the start of tooth movement, there were no odontoclasts observed around the teeth. Five and 7 days after, odontoclasts expressing OPN mRNA appeared on the surface of the root. The cells were multinuclear and positive for TRAP staining. Most expressed OPN mRNA strongly, however, some TRAP-positive odontoclasts did not express OPN mRNA. Fourteen days after the start of tooth movement, odontoclasts were not observed. Expression of OSC mRNA was observed in osteoblasts and lining cells, but not observed in odontoclasts 7 days after tooth movement. Fourteen days after the start of tooth movement, the cells observed in the resorption lacunae on the root surface did not express OSC mRNA. Conclusions:The present findings suggest that OPN may play an important role in root resorption the same as those in bone resorption during experimental tooth movement.