FACTORS INFLUENCING DENTAL CARIES 277 



bacteria which are confronted with the metabohsm of copious 

 amounts of carbohydrates, often in the form of hypertonic sugar 

 sokitions. Perhaps the organisms have httle choice other than rapid 

 metabohsm, accelerated reproduction, or polysaccharide storage 

 (Gibbons and Socransky, 1962). (The latter phenomenon may also 

 represent a protective mechanism whereby less aciduric organisms 

 can delay the conversion of large quantities of carbohydrate and 

 thus control the release of unfavorable amounts of free acid. Poly- 

 saccharide storage apparently immobilizes part of the carbohydrate 

 for future metabolization at a gradual rate. ) 



We have found these questions intriguing and have found it in- 

 teresting to speculate on possible mechanisms which might affect 

 bacterial activity from what is known about the inorganic ion re- 

 quirements of streptococci, changes in the carbonate content of 

 enamel containing fluoride (Brudevold, 1962fl; Nikiforuk et at., 

 1962; Middleton, 1962), and the loss of carbonate and magnesium 

 from carious enamel and dentin ( Johansen, 1962 ) . 



Along these lines the report of Brown et al. (1962) merits com- 

 ment. These workers postulated that essential nutrients diffusing 

 from within the tooth might support growth of invading micro- 

 organisms and thus play a role in caries. In an in vitro system of 

 special design it was possible to demonstrate that organisms pene- 

 trated dentinal tubules when the crowns of teeth were covered with 

 a niacin-deficient medium, and the growth of Lactobacillus arabi- 

 nosiis depended on the diffusion of niacin from the pulp side of the 

 teeth. The principles of this system and the implications of the find- 

 ings are of considerable interest, as are the original demonstrations. 

 Invasion seems to be related to dependence of organisms upon es- 

 sential factors. 



Clinical and Therapeutic Implications 



The matters discussed have a bearing on the clinical disease. We 

 do not know whether human caries is largely a specific type of 

 microbial infection, particularly in the initial stages. The etiologic 

 role lactobacilli and other acidogenic organisms play in human 

 caries needs further clarification. On the basis of such findings im- 



