OBJECTIVETo investigate the immunolocalization of receptor activator of nuclear factor-kappa B ligand (RANKL) and osteoprotegerin (OPG), and to explore the correlation between their expressions and activity of osteoclast during first mandibular molar eruption.

METHODSMouse mandibles dissected from postnatal day 1.5 to 14.5 were stained respectively for multinucleated osteoclasts using tartrate-resistant acid phosphatase (TRAP) staining, and RANKL and OPG protein expression was examined by immunohistochemical staining.

RESULTSThe two peak values of osteoclast/acreage in the occlusal and basal region were both observed on the P1.5 and P9.5; while the two peak values in the lateral region were on P3.5 and P9.5. During the mouse molar eruption, burst of osteoclastogenesis was associated with high expression of RANKL and low expression of OPG.

CONCLUSIONSRANKL and OPG could have a close relationship with the osteoclast activity and two developmental apexes were observed during the molar eruption. The occlusal movement was relatively stable, meanwhile the temporarily accelerative movement to the basal and lateral regions could occur.