Second permanent molars: embryological origin, development and eruption. Role of the RANK/RANKL/OPG pathway

Craniofacial skeleton formation, and more specifically alveolar bone development, follow a finely regulated controlled genetic program. A spatial and temporal combination of molecular signals determines the type and inter- and intra-maxillary position of each dental-alveolar unit. The volumetric growth and movement of tooth germs depend on a coordinated adaptive peripheral alveolar bone modeling process which is supported by signaling pathways between cells of the dental epithelium, dental follicle and alveolar bone. These signaling pathways involve transcription factors, proto-oncogenes and diffusible factors called “growth factors”. Transient impairment of these signals during time windows corresponding to the development of the various dental types could explain specific localized eruption deficits in a given dental type, as observed for second molars. Ongoing studies show that disturbances of bone resorption related to disruption of the RANKL/RANK/OPG signaling pathway affect tooth eruption and root morphogenesis, with a clear relationship between the time window of onset of disruption and the affected dental type