[Effects of post-natal inhibition of RANKL on molar eruption and root formation in C57BL/6 mice].

INTRODUCTION: Recent observations performed in the orthodontic department of La Pitié-Salpêtrière hospital in Paris reported an increase of non-familial eruption defects of permanent molars. Our recent data have evidenced the involvement of osteoclasts (OC) in both the eruption and the dental retention processes through the RANKL/RANK/OPG signaling pathway. These facts are at the origin of the hypothesis of the existence of an environmental etiology for those eruption defects that would correspond to the perturbation of cellular autocrine/paracrine signaling pathways as the RANKL/ RANK/OPG.

MATERIALS AND METHODS: C57BL/6 mice were submitted to repeated injections with anti-RANKL neutralizing antibody during the nine days following birth. A phenotypic comparison with transgenic mice overexpressing RANK was performed for the functional characterization of the RANKL/RANK/OPG pathway. The dento-alveolar complex was analyzed using micro-CT for bone density and Masson's trichrome staining for histological examination.

RESULTS: The RANKL transient invalidation of RANKL stopped the molar root development and tooth eruption contrary to transgenic mice overexpressing RANK. The recruitment and the OC activity were strongly impacted.

DISCUSSION: This research is of direct clinical interest in understanding the pathology of eruption as indirect in establishing orthodontic treatment protocols for particular cases.