926 



GENERATION. 



The permanent teeth are developed beneath the follicles of the temporary, or milk- 

 teeth. The first appearance is a prolongation or diverticulum from the enamel-organ of 

 the temporary tooth, which dips more deeply into the mucous structure. This becomes 

 the enamel-organ of the permanent tooth ; and the successive stages of development of 

 the dental follicles and the dental pulp progress in the same way as in the temporary 

 teeth. As the permanent teeth increase in size, they gradually encroach upon the roots 

 of the temporary teeth. The roots of the latter are absorbed, the permanent teeth ad- 



FIG. 306. Temporary and permanent teeth. (Sappey.) 



1, 1, temporary central incisors ; 2, 2, temporary lateral incisors ; 8, 3, temporary canines : 4, 4, temporary anterior 

 molars; 5, 5, temporary posterior molars; 6,6. permanent central incisors; 7,7, permanent lateral incisors; 

 8, 8. permanent canines ; 9, 9, permanent first bicuspids ; 10, 10, permanent second bicuspids; 11, II, first molars. 



vance more and more toward the surface, and the crown of each temporary tooth is 

 finally pushed out. The number of the temporary teeth is twenty, while there are 

 thirty-two permanent teeth. Thus there are three permanent teeth on either side of 

 both jaws, which are developed de novo and are not preceded by temporary structures. 



The first dental follicles usually appear in regular succession. The follicles for the 

 internal incisors of the lower jaw appear first, this occurring at about the ninth week. 

 All of the follicles for the temporary teeth are completely formed at about the eleventh 

 or the twelfth week. 



The temporary teeth appear successively, the corresponding teeth appearing a little 

 earlier in the lower jaw. The usual order, subject to certain exceptional variations, 

 according to Sappey, is as follows : 



The four central incisors appear from six to eight months after birth. 



The four lateral incisors appear from seven to twelve months after birth. 



The four anterior molars appear from twelve to eighteen months after birth. 



The four canines appear from sixteen to twenty-four months after birth. 



The four posterior molars appear from twenty-four to thirty-six months after birth. 



