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What seems to be the same kind of partial decalcification may be produced experimentally by solutions of organic acids, such, for instance, as lactic acid—the one generally supposed to be the most important in caries production. However, weak solutions of

Fig. 8. Piece of the bacterial film from over early stage caries lesion. Specimen teased off, stained very lightly with safranin and mounted in 50 per cent glycerin for photographing by transmitted light. Note filamentous nature of bacterial material (1) and growing ends and fruiting heads at outer surface (2). Inner surface (3).

Fig. 9. Bacterial film pile on surface of tooth over early stage caries ( chalky enamel ) stained lightly with safranin and photographed with incident light. Note mound of L. racemosa (1) with some fruiting heads focused around periphery (2). Many more just out of focus.

organic acids, such as can be assumed to be formed at caries disposed locations, act very slowly. It is only after long continued exposure to such weak acids experimentally that demonstrable partial decalcification occurs. Likewise it is only after long continued and repeated production of acids by bacterial action, that a caries lesion results. It is very apparent that to prevent early stage caries at any vulnerable place on a tooth, it is necessary to prevent the formation of acids by bacteria growing there*

 

Time Factor In Production of Acids By Bacteria

Some bacteria grow and produce acids much more rapidly than others. However any of them require considerable growing time, under the most favorable conditions, for production of appreciable amounts (or strengths). Perhaps the most familiar example for those who have been medical or dental students is the testing of acid production by pure cultures of different bacteria inoculated into litmus milk. Litmus milk is blue. A tube of such culture media inoculated with a loopful of a pure culture of an acid producing organism and placed in the incubator still remains blue for several hours, usually twelve or fifteen or more. After the necessary incubation time it will be noted that the color is changing to a faint pink and finally, within twenty-four hours or a longer period, to red, indicating production of considerable lactic acid from the sugar in the milk.Stephan and Millers showed that brushing the teeth thoroughly before rinsing with 10 per cent glucose solution eliminated the fall in pH which otherwise would have occurred. They found that in testing plaque material in situ for pH drop following the glucose rinse, subjects who refrained from brushing their teeth for three or four days, thereby insuring a sufficient amount of bacterial material on accessible surfaces, gave most satisfactory results. Therefore a considerable period of time is required for sufficient growth and accumulation of bacteria to occur before much acids can be produced in the presence of carbohydrates.

*Note: I am aware of the suggestion, belief or claim by recent authors (6, 7, 8, 9, 10, 11, 12, 13, 14) that caries is, to some extent, a proteolytic process by which the organic material of the enamel is invaded and broken down by the enzymes of proteolytic bacteria and that this is followed or accompanied by disintegration or decalcification of the inorganic material. The personal oral hygiene for prevention herein specified would be equally applicable to such order of events in the caries process.

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