Morphodifferentiation of Teeth in Embryonic Mandibular Segments in Tissue Culture

tion and localization of organ rudiments is revealed sooner or later by the presence of chemo-differentiated material or morphoge-netic substances in certain places which may be called fields or areas of differentiation of organs. " These authors based their conclu-sions on much experimental work with lower animals. With a view to applying this prin-ciple to the dentition as a whole, as well as to individual teeth, Butler2 studied the teeth of Cenzoic mammals and concluded that "... the teeth are repeated organs that oc-cupy different positions in a continuous mor-phogenetic field. " He thought that, as yet, there was no experimental evidence to indi-cate these factors involved in the determina-tion of dental form. Neither grafting experi-ments nor the growth of teeth in vitro had demonstrated existing field gradients. This may be partly true, but Glasstone3 has shown that, in isolated molar tooth germs cultivated in vitro, there is a morpho-genetic field within the tooth itself. She also has demonstrated that, although the cusp-forming regions are morphologically deter-mined in the tooth germ, regulative changes can take place at an early stage of develop-ment.4 Pourtois5 studied the mandibles of 812- to 12-day mouse embryos by tissue culture technics. In explants taken from embryos younger than 1012 days, there was little development in vitro but mandibles ex-planted at later stages showed some, but not much, further differentiation. The present study was made to find whether there is a morphogenetic field within the mandible itself. It was decided to explant different parts of the mandible at an early stage of differentiation and examine This investigation was supported by a grant from the