FOURTH PERIOD. 



LEVELING OF THE PERMANENT INCISORS. 



During this period the signs furnished by the dental appa- 

 ratus become more difficult to recognize, and the determination 

 of the exact age is less precise than at an earlier period. The 

 points to be examined from six years are, first, the wearing of 

 the corner teeth, the form of the transverse diameters of the 

 teeth, the position of the central enamel on the surface of the 

 table, and the general outline of the incisive arch. 



At six years, after the complete leveling of the teeth, the 

 tables of the pinchers commence to become oval in shape. The 

 posterior border of the corner teeth has become worn and the 

 cup is completely separated from, the peripheral enamel. The 

 cement disappears from the anterior face of the pinchers, so that 

 they become whiter in color. Very frequently at this age the 

 notch commences to show on the outer border of the superior 

 corner teeth. 



At seven years, all of the teeth are denuded of cement on 

 their outer faces and are much whiter in color. The inferior 

 corner tooth, which is narrower from in front to behind than the 

 ' superior, wears only the anterior portion of the latter and makes 

 distinct, in profile, the notch which we have just seen often 

 commences at six. The pincher teeth become narrower from 

 side to side, and the oval of the posterior border shows a pro- 

 jection backward ; the intermediate teeth become oval, and, in 

 both, the cups become decidedly narrower and are found nearer 

 the posterior border of the teeth. In profile, the incidence of 

 the jaws has altered from the convex arch of six years and 

 tends to assume the form of an ogive. 



At eight years, the incisors commence to turn from a white 

 to a yellowish white. The arches are narrower from side to 

 (92) 



