CHAPTER I 

 DEVELOPMENT OF THE TEETH IN MAMMALIA 



THE two principal tissues of the teeth are enamel and 

 dentine, enamel being derived from the ectodermic epi- 

 thelium of the mouth and dentine from the mesodermic 

 submucous tissue. 



The enamel organ is the first part of the tooth germ to 

 appear, the dentine papilla arising later, although it is the 

 first to show commencing calcification. 



While, however, the appearance of an epithelial inflection Epithelial 

 is the most constant indication of tooth formation, it does mflectlon 

 not necessarily point to the future formation of enamel. 



Tooth germs are developed, not upon the surface, but 

 always at some little distance within the tissues, and in 

 their simplest form consist of dentine and enamel only, bnt 

 the future tooth is determined by the epithelial inflection 

 rather than by the dentine germ, which is a subsequent 

 production of the mesodermic tissue. 



It is only in comparatively recent times that a clear 

 understanding of the mode of development of the teeth has 

 been arrived at. 



The views held by Goodsir (7) were for long accepted as 

 giving a true explanation of the process of tooth develop- 

 ment, and were adopted by Professor Owen and many other 

 eminent authorities. 



Goodsir considered that the first indication of tooth Views of 

 formation was the appearance of a groove which he called 

 ' the primitive dental groove ', and that this was followed 

 by a papillary stage, a follicular, and an eruptive stage. 

 This primitive dental groove we now know was not a groove 

 but a band. The epithelial band is formed from the cells 

 of the deeper layer of the epithelium of the mouth, and is, 

 by the proliferation of these cells, prolonged downwards 

 into the mesodermic tissue as a continuous band, passing 

 horizontally along the line of the future jawbones. The 



