The Role of the Dental Lamina in Mammalian Tooth Replacement

We have applied the ferret, Mustela putorius furo, as a model for tooth replacement. Ferret has a heterodont dentition, which includes all tooth families, and all antemolar teeth are replaced. Compared with mouse, the ferret therefore has a less derived mammalian dentition resembling that of humans. We have studied tooth replacement in serial histological sections in embryonic and young postnatal ferrets. Our observations indicate that the replacement teeth form from the dental lamina that is intimately connected to the lingual aspect of the deciduous tooth enamel organ. It grows as an offshoot from the enamel organ, elongates in cervical direction and later buds to give rise to the replacement tooth. The extent of the dental lamina growth, preceding replacement tooth budding, varied between different teeth. The dynamic gene expression patterns of Sostdc1, Shh and Axin2 brought new insight into the signal networks regulating the tooth replacement process. The distinct expression of Sostdc1 at the interface between the dental lamina and the deciduous tooth is the first indication of a specific tissue identity of the dental lamina. We suggest that the reactivation of a competent dental lamina is pivotal for the replacement tooth formation. J. Exp. Zool. (Mol. Dev. Euol.) 312B:281-291, 2009. (c) 2009 Wiley-Liss, Inc.