A comparative study of the development in vivo and in vitro of rat and rabbit molars

Although the normal embryology of mammalian teeth has been carefully studied, little is known of the developmental mechanics of teeth. The present communication is concerned with the problem of cusp formation. The main object of the investigation was to find how far the formation of molar cusps was due to extrinsic factors in the jaw and how far to intrinsic factors in the tooth germ itself. Previous work (Glasstone 1936) had shown that embryonic teeth grown in vitro and removed from the general influence of the body continue to develop. In these earlier experiments the rudiments were explanted when cusps had already appeared but before odontoblasts and dentine had differentiated. In the present experiments the tooth germs were explanted at an earlier stage before the cusps had begun to form, to see whether cusps would develop in vitro in the isolated rudiment and if so whether they would correspond in number, shape and arrangement with those of the normal embryonic tooth.