DEVELOPMENT OF THE TEETH 



153 



DEVELOPMENT OF THE TEETH 

 The enamel organs, which give rise to the enamel of the teeth and are the 

 moulds, so to speak, of the future teeth, are of ectodermal origin. There first ap- 

 pears in embryos of about 1 1 mm. an ectodermal downgrowth, the dental ridge or 

 lamina, on the future alveolar portions of the upper and lower jaws (Fig. 159). 

 These laminae are parallel and mesial to the labial grooves. At intervals, on 



' Lower lip 



Mandible 



Labial groove 



Dental papilla 

 Dental lamina 



Fig. 159. — Early stages in the development of the teeth (Rose). A, at 17 mm. (X 90); B, at 41 mm. 



(X 45). 



each curved dental ridge or lamina a series of thickenings develop, the anlages 

 of the enamel organs (Fig. 160). Soon the ventral side of each enamel organ be- 

 comes concave (fetuses of 40 mm. C H) forming an inverted cup and the con- 

 cavity is. occupied by dense mesenchymal tissue, the dental papilla (Figs. 159 B 

 and 162). An enamel organ with dental papilla forms the anlage of each decid- 



Oral epithelium ^"''"''^ °''&<^'^^ 



Dental i 



Papilla: 



B 



Enamel organs 

 C 



Nfcks of enamel organs 

 D 



Free edge of 

 the dental 

 lamina 



Fig. 160. — Diagrams showing the early development of three teeth. One of the teeth is shown in vertical 



section (Lewis and Stohr). 



ual or milk tooth. Ten such anlages are present in the upper jaw and ten in 

 the lower jaw of a 40 mm. fetus. The connection of the dental anlages. with the 

 dental ridge is eventually lost. The position of the tooth anlage between the 

 tongue and lip is shown in Fig. 163. 



