Syphilitic Teeth \ \ 3 



Hexagonal rods of enamel cover the working part of the tooth and 

 protect the less durable dentine ; when they are worn away the den- 

 tine soon perishes. 



The crusta pctrosa is a thin layer of bone which covers the hidden 

 surface of the tooth ; it contains rudimentary Haversian systems. In 

 old people outgrowths from it are apt to form large exostoses. 



Development of the teeth. In the second month the margin of 

 the rudimentary jaw is marked by a primitive dental groove ; the 

 enamel is developed from the epithelial lining of this groove. The rest 

 of the tooth grows up as a small papilla from the subjacent part of the 

 groove and eventually becomes capped with the enamel. Each rudi- 

 mentary and temporary tooth then becomes shut into a separate com- 

 partment of the dental groove, the small chamber constituting the 

 dentinal sac. The permanent teeth are developed in secondary 

 dentinal sacs which are budded off from the backs of the primary 

 sacs. 



Eruption. It is impracticable to remember when each tooth of 

 the two sets should be making its appearance, but every student 

 should know that the first tooth of the milk-set is cut in the seventh 

 month, and the first of the permanent set in the seventh year. The 

 lower teeth appear before the upper, and the eruption of the lower 

 central incisors should be taken as a hint that the child should be 

 weaned. In the first set the lateral incisors appear after the central, 

 and, at the end of the year, the first molars : then come the canines, 

 and, in the second or third year, the back molars. 



As regards the permanent set, in the seventh year the first lower 

 molars appear. In the seventh and eighth years, respectively, the 

 middle and lateral incisors emerge. In the ninth, tenth, eleventh, and 

 twelfth years come the first and the second bicuspids, the canines, and 

 the second molars ; just before the subject comes of age he is supposed 

 to have cut his wisdom teeth. 



It should be noticed that the temporary incisors, which are cut well 

 within the first year, must needs be formed and calcified many months 

 earlier, and that when hereditary syphilis attacks the mouth it is 

 powerless to affect them. In the first year or two, however, when the 

 congenital taint is exerting its prejudicial influence on nutrition, the 

 teeth of the permanent set are being developed. They, therefore, and 

 not those of the milk teeth, are de- 

 faced by the disease. Syphilitic teeth 

 are unevenly arranged, and their /J 

 narrowed cutting edge is marked by " 

 a crescentic notch. The test-teeth ' 

 of Hutchinson are the central, upper incisors of the permanent set. 



If the teeth of the permanent set are very large, or the alveolar 

 processes are too small to hold them, one or more of them may fail to 

 reach the surface, and may migrate towards the antrum, or nasal fossa. 



I 



