AGE, AS INDICATED BY THE TEETH. 



311 



black. As the tooth wears down, the hollow of course disappears; but 

 the surface of the dentine immediately below the original hollow, being 

 a somewhat soft material, has become stained for some distance down. 

 Thus there still is a black mark. With the further wear of the tooth the 

 stained portion of the dentine wears away, and the ''mark " is then said 

 to be out. The mark, as the reader will easily see from this description, 

 is in a constantly changing condition. 



Premising that the time, which the mark will take to wear out, will 

 vary to a greater or less degree according to certain circumstances de- 

 tailed hereafter, the following are general rules for guidance. 



Between three and five years old the marks are very plain in all the 

 permanent incisors. Fig. 143 and 143. At six, the marks are wearing out 

 of the two centre teeth, which came up at three years old. They are 

 plain in the two next, and perfectly fresh m the two corner teeth. 

 Fig. 144. 



At seven, the marks have disappeared from the centre teeth, are wear- 

 ing out of the two next, and are distinct and plain only in the corner 

 teeth. Fig. 145. 



Fig. 145. 

 The Mark at Seven Years. 



At eight, the marks have disappeared from all but the corner teeth, 

 in which they are becoming indistinct. Fig. 146. 



At nine, the marks are not usually found in any of the teeth. Fig. 147. 



For about two years after the mark has disappeared in each tooth, 

 there may still be seen in the form of a star a trace of the enamel which 

 lined the bottom of the original hollow, and which underlies it for some 

 depth. This star of course decreases in size with the wear of the teeth. 

 About twelve or thirteen the last traces of the enamel have usually dis- 



