Studies of Dental Caries. 



7 



also, by the fact that strontium, after its oral administration (as 

 the chloride), daily for some time to young dogs, accumulates in 

 the solid parts (and is present in the pulp) of the first and second 

 sets of teeth, apparently taking the place of calcium. We have 

 not yet determined whether strontium substitutes calcium, in 

 such experiments, in the enamel of fully erupted teeth. 



Experiments with arsenic, in the forms of salvarsan and 

 arsenite (analogous to those with strontium), in an effort to 

 determine whether arsenic can displace, or associate with, phos- 

 phorus in dental calcification, have given us wholly negative 

 results. 



Practically all the biochemical results referred to, thus far in 

 this statement, were obtained on teeth in process of development. 

 It has been cumulatively evident, as our experiments increased 

 in number and scope, that internal secretions can have little or no 

 effect, directly or indirectly, on the enamel of fully developed and 

 erupted teeth (and therefore can have little or no continuing direct 

 bearing on the problem of caries in such teeth) unless one or more 

 physiological substances can pass from pulp through dentin into 

 normal enamel, or from oral fluids into such enamel. 1 



We find that water passes freely back and forth through all 

 parts, including the enamel, of fully developed natural extracted 

 teeth. Simple mineral salts, such as sodium chloride, and common 

 organic substances, such as cane sugar, show similar ability to 

 diffuse back and forth through fully developed natural extracted 

 teeth. 



Our results in this general relation indicate that, whether or 

 not there is true nutritive or maintenance metabolism in normal 

 enamel, there may be physiological or pathological exchange of 

 materials in enamel by diffusion from blood through dentin and 

 enamel to oral fluids, and vice versa. 



In the course of our study of the nature of tooth composition, 

 from the point of view of effects of internal secretions on dentition 

 (in their relation to the problems of cause, control, and prevention, 

 of dental caries), we have found that teeth contain a glyco-protein 

 that is closely similar to osseomucoid, and is evidently analogous 

 to, though not the same as, salivary mucin. 



1 This statement ignores provisionally the possibility that caries may occur 

 from changes in dentin that merely undermine enamel. 



