HANKE, MILTON T.: Chicago, Ill. (May 10, 1939).

 [In collaboration with members of the Chicago Dental Research Club.]

(1) A suspension of 0.1 gm. of powdered enamel in 20 cc. of distilled water has a pH of 7.7 to 8.0. Addition of 1 cc. of 0.1 N hydrochloric acid dissolves some of this enamel and lowers the pH to 5.5 to 5.65; 3 cc. of 0.1 N hydrochloric acid dissolves considerable enamel, and lowers the pH to 4.8 to 5.0. This shows that enamel is soluble at higher pH levels than has heretofore been supposed, and implies that ordinary acid-forming bacteria in the oral cavity—even those that are not particularly acidogenic—could produce suf­ficient acid to dissolve appreciable amounts of enamel. (2) A yellow solution of methyl red turns bright red when placed in contact with superficially dried carious enamel or dentin, in situ or in freshly extracted teeth, a result that proves the presence of a high degree of acidity in this carious structure. This is a degree of acidity sufficient to dissolve enamel. (Methyl red is bright red at pH 5.0 or below.) (3) Oral bacteria convert cane sugar and other carbo­hydrates into acids. Cane sugar can be demonstrated in saliva for at least one hour after ingestion, showing that carbohydrates (certainly cane sugar) are a real menace to the teeth for at least one hour after ingestion. This is not true, if the mouth is thoroughly rinsed with water after the carbohydrate is ingested. (4) The difference between caries-immunes and caries-susceptibles is due locally to the quality of their salivas. Saliva secreted by a caries-immune is always alkaline in reaction and capable of neutralizing considerable acid;

whereas a caries-susceptible may secrete saliva that is either alkaline or acid in reaction, but poorly buffered and never capable of neutralizing much acid. These facts have been determined on samples of saliva collected prior to 10 : 00 A.M. Highly susceptible persons may secrete fairly well buffered saliva at various times of the day, especially after meals. (5) The regions of stagna­tion are multiplied in mouths in which chronic gingivitis occurs. Diets rich in vitamin C are definitely antagonistic to gingivitis. (6) Alkalinizing diets— rich in fruits, vegetables, and milk—arrest or prevent caries in about 50 percent of normal children. In many cases, alkalinizing diets, even when augmented with large amounts of vitamins A and D, do not arrest or prevent caries.

(7) The teeth of caries-immunes are protected by saliva because it is well buffered, not because it is alkaline. Although plaques frequently occur on teeth of immunes, good-quality saliva penetrates and readily neutralizes acids in these plaques, and thus prevents development of degrees of acidity that damage enamel. In some persons individual plaques are so thick that even well buffered saliva cannot permeate them, and underlying surfaces may decay. (8) Plaques, consist­ing of filamentous microorganisms, bacteria, and epithelial cells, always occur on teeth in regions that have not been thoroughly cleansed mechanically. Teeth usually have plaques that may be either alkaline or acid to methyl red. Alkaline plaques usually become acid 15 to 30 minutes after ingestion of cane sugar, showing that sugar is absorbed to some extent by plaques and that microOrganisms therein can, even in 15 minutes, produce amounts of acid that may damage enamel. The desirability of removing all plaques is obvious. (9) Plaques consist pre­dominantly of filamentous microOrganisms intermeshed in a matlike structure, the interstices of which are more or less filled with bacteria and occasional epithelial cells. Plaques on dental areas of stagnation in habitual candy-eaters are often so impregnated with syrup, even 30 minutes after candy has been eaten, that the plaques when transferred to glass slides cannot be dried until they have been washed with water. Such plaques are highly acid in reaction, and not infrequently have odors resembling that of butyric acid. The structure of a plaque is similar to that of blotting paper, and is capable of holding sugar and acid in contact with enamel for a long time. Acids developed in a plaque etch and finally produce clinical cavities in enamel. (10) Plaques disappear from teeth that are given ordinary care, if the mouth is also carefully rinsed once or twice daily with solutions that contain organic mercurials. Best results are obtained when these solutions are retained and ” swished ” thoroughly for a period of two minutes. A 1 : 5000 solu­tion of any of the commercial organic mercurials is effective; but all of them exhibit undesirable effects, if used for a long time, such as discoloration of teeth ; amalga­mation with gold fillings, inlays or other restorations ; metallic taste ; and, in some cases, even suggestions of mercury poisoning. A 1: 5000 solution of sodium para-hydroxy-mercury-benzoate (Na-0O3-C,,H4-Hg-OH) is effective and free from the above objections. Clinical experience with this solution for the purpose of removing plaques, and possibly preventing caries, extends over a period of three years. Observations on a limited number of persons during this period indicate that caries can be arrested in some cases by the regular use of this solution.

References: Numerous since 1929; J. Am. Den. Assoc., 1929, 1930 ; J. Nutr., 1931; Den. Cosmos, 1933 ; Int. J. Orth. Oral Surg., 1933 ; Den. Digest, 1937 ; Diet and dental health, 1933 (University of Chicago Press) ; Nutrition et dentition, 1937 (Hermann and Co., Paris).

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