CHANGES PRODUCED ON THE FACE. 255 



CHANGES PRODUCED ON THE UPPER AND LOWER JAW AND FACE, 

 FROM THE DEVELOPMENT OF THE TEETH. 



During the period of the first and second dentition, great 

 and obvious changes are noticed in the face, resulting from 

 changes occurring in the upper and lower jaw bones, from 

 development of the teeth. 



The principal of these changes we will briefly notice, to 

 impress upon the student the great and commanding in- 

 fluence which the teeth simply exert during their develop- 

 ment, in producing the various configurations of the face, 

 observed at different periods. The first we notice is in the 

 dental arches. The maxillary bone, as stated in another 

 place, presents in the first instance a simple groove, scarcely 

 perceptible when the tooth germs are present, but which 

 soon becomes partitioned off and formed into alveoli for the 

 accommodation of the two sets of teeth. After the per- 

 manent set have completed their eruption, we find but a 

 single range of alveoli ; and when, as in old age, the teeth 

 are lost, the alveoli are destroyed and the arches again re- 

 turn to their original embryo state. 



The alveolar arches, when the teeth are being developed, 

 show striking changes in their length and height. The 

 length of the arches depends upon the volume and number 

 of the teeth, and Blandin says it may be safely asserted 

 that the arches grow from the " beginning of life," to the 

 full development of the dens-sapientae. These arches, in 

 the adult, are separated by drawing a transverse line in 

 front of the first molar, into an anterior and a posterior 

 portion. 



All the alveoli belong to the first portion till the appear- 

 ance of the first permanent molar in the fifth year. The 

 alveolar arch now extends itself back to make room for 

 the second molar and wisdom teeth, and on their appear- 

 ance, the anterior and posterior portions are of equal 

 length. 



The changes in height of the alveolar arches, seem to 

 be regulated by the development of the roots of the teeth. 



