THE MARK AND DENTINAL STAR. 



(Illustrated on page 215.) 



The mark (also called central enamel, infundibulum, 

 &c. ) is composed of enamel, the hardest of the three con- 

 stituent parts of the teeth — enamel, dentine, and cement. 



The dentinal star, so called because it is composed of 

 dentine, appears about the ninth year. It has a yellow 

 tint, which is the best means of distinguishing it from 

 the mark. Its appearance is accounted for as follows : 

 When the tooth wears nearly to the pulp or nerve cavity, 

 the pulp becomes gradually converted into dentine, fill- 

 ing the upper part of the cavity from the inside as per- 

 fectly as a dentist can fill a cavity from the outside. The 

 star is visible eight or ten years. After it is worn out, 

 there will be a cavity of course. 



