[For himself and co-workers in the ” Michigan Group Research on Dental Caries” (1924-37): (bacteriologists) PHILIP JAY, FAITH P. HADLEY, MARY CROWLEY, EDNA DELVES; (nutritionists) MARTHA KOEHNE, ELISE MORRELL; (chemists) REBECCA HUBBELL, JULIUS WHITE; (dentists) DOROTHY G. HARD, WILLIAM H. MCCRACKEN.]
(1) No consistent relationship has been found between hardness or perfection of teeth, nor state of mouth hygiene, and activity of caries. (2) No correlation has been demonstrated between amounts of salivary calcium, phosphorus, chlorides, pH, CO2-capacity, total alkalinity, total solids, or ash, and activity of caries. (3) No relationship has been demonstrated between intake of calcium, phosphorus, or acid/base dietary values, and activity of caries. (4) Inherited tendencies or inherent individual characteristics, in a small percentage of cases, are more important determining factors in caries than ordinary dietary conditions. A great majority of caries-susceptibles, however, can be benefited apparently by adoption of very simple dietary measures.(5) There is no evidence that caries is produced by malnutrition, or may be prevented by adequate diets. (6) Sugar is a very important causative factor in caries. A remarkably low degree of caries was observed in children on a low-sugar diet deficient in calcium, phosphorus, and vitamin D. Active caries was induced in children by increasing the sugar intake while they were receiving a diet that nutritionally was adequate. Ingestion of low-sugar diets by children is conducive, as a rule, to freedom from caries. (7) The most constant differential between caries-free and caries-susceptible persons, thus far demonstrated, is that of relative number of L. acidophilus organisms in the mouth. This correlation is approximately 90 percent positive. (8) An immunologic principle related to L. acidophilus has been demonstrated in blood of caries-free persons, in whose mouths, as a rule, L. acidophilus does not exist ; and when planted therein promptly disappears.
Bacteriology. In studies of caries by qualitative cultural methods and smears, L. acidophilus was present in every initial lesion, and on the teeth in a small percentage of caries-free mouths ; although smear preparations showed that, in the latter cases, the growths were much lighter than for cases of active caries. L. acidophilus, in fermentation of carbohydrates, produced acids (pH from 3.8 to 5.0), any of which in the resulting proportions were capable of decalcifying enamel. In a survey of 1335 children of various ages, there was close correlation of L. acidophilus and caries. Caries developed in previously caries-free mouths when the organism was present over relatively long periods. When the organism disappeared from the mouth, active caries ceased. Oral acidophilus, as compared with intestinal acidophilus, exhibited cultural variations that could not be differentiated on the basis of the colony appearance claimed by Morishita and Rettger. The following distinctive differences in the oral flora of caries-susceptible and caries-free persons, with reference to L. acidophilus, have been shown : (a) Diminished frequency of occurrence of L. acidophilus in caries-free groups ; (b) qualitative difference in type of L. acidophilus isolated ; (c) diminished frequency of L. acidophilus localized on tooth surfaces in caries-free groups ; (d) presence, in caries-free groups, of a type of organism rarely encountered in the susceptible group. (These findings were duplicated in the intestinal tracts of the same individuals.) A quantitative method of estimating number of L. acidophilus in saliva was devised, using a modification of Kulp’s tomato-peptone agar. By this method direct correlation between counts of salivary L. acidophilus and activity of caries was found. In caries-susceptibles the number of L. acidophilus in saliva is directly proportional to the amount of carbohydrate ingested. Many attempts were made to implant known strains of L. acidophilus in the mouths of persons who were immune to caries, and in the mouths of rats, but in each instance these attempts were unsuccessful. L. acidophilus agglutinins can usually be demonstrated in blood serum of caries-free persons. As a rule, acidophilus agglutinin-titres are low or absent in cariessusceptibles. By administration of vaccine containing the R phase of L. acid‑ophilus, agglutinin titres against that organism in caries-susceptibles may be raised to those of caries-free persons. Intradermal injections of L. acidophilus filtrates produced definite skin-reactions in caries-susceptibles. Similar administrations to caries-free persons usually produced little or no reaction. When polyvalent L. acidophilus vaccines were given to caries-susceptibles, the skin reactions in several became negative, and there was increase in L. acidophilus agglutinin-titres. Unfortunately, administration of this vaccine was attended by severe inflammatory reactions at the sites of inoculation.
Chemistry. No relation was found between H-ion concentration of saliva and activity of caries, nor between calcium and phosphorus contents in saliva and caries. In one group of hospitalized children, salivary C00-combining power of those who were caries-free was 44 percent higher than of those of the same age who had active caries. The alkalinity of saliva of the caries-free children in this group was 24 percent higher than that in children of the same age having active caries. These findings did not obtain in similar salivary analyses of other groups of children. The values for total solids, ash, calcium, phosphorus, chlorides, diastatic activity, and pH showed no consistent differences between the caries-free and caries-susceptible groups. In blood sera, contents of calcium, inorganic acids, and soluble phosphorus, also CO2-capacity and pH values, were the same for both groups. In nutritional studies of another group of caries-susceptible children, no correlation was found between CO2-capacity, or calcium or phosphorus content, of saliva and activity of caries. There was also no significant variation in absorption or retention of calcium or phosphorus. In studies of nitrogen, calcium, and phosphorus retentions, on high-sugar diets—when not more than 6 percent of the caloric value was provided by sugar—there were no significant differences. However, when sugar intake was increased to 16 to 18 percent of the caloric value, there was a tendency toward increase of nitrogen and phosphorus retentions ; in some cases calcium retention was slightly decreased. The reaction (pH), and ammonium content, of activated saliva (paraffin) showed marked variations. No significant difference between salivary ammonia in caries-free and caries-susceptible individuals, as suggested by Grove and Grove, could be demonstrated. Resting saliva had higher calcium and phosphorus contents, and lower CO2-capacity, than activated saliva, but there was no apparent relationship between these constituents and caries.
Nutrition. Caries was produced, in rats, by various inadequate diets ; but did not occur on markedly deficient diets that were free from fermentable carbohydrates. (The subsequent work of Hoppert, Weber, and Canniff, showing that the physical properties of diets are much more important in the production of caries in rats than any other dietary factor, qualifies the value of these findings.) When the regular home-diet of a group of children was supplemented by 1 quart of milk and 2 ounces of tomato juice, either with or without viosterol, a slight tendency toward decrease of caries was noted, but there was no change in the salivary content of calcium or phosphorus. Low-sugar diets, for a group of hospitalized children under strict nutritional control, resulted in definite arrest of caries in a 11: centage of cases. When to these diets large amounts of sugar were added, caries increased in most cases. The correlation of L. acidophilus with activity or arrest of caries was 88.9 percent. In a selected group of children in an orphanage, under strict supervision, no correlation could be found between caries and (a) height or weight, (b) sex, (c) CO2-carrying power of saliva, or (d) intake of calcium, phosphorus, or vitamin D. Observations of these orphanage children, over a period of several years, showed that a great majority had almost no caries. Only 10 to 15 percent had any appreciable dental disease. These remarkable dental conditions occurred despite the fact that these children received an inadequate diet that was low in calories, calcium and phosphorus, and vitamins. An important feature of the diet was the fact that sugar consumption had been kept consistently low. In a group of 51 children in an orphanage, on low-sugar diets continued over a period of seventeen months, only 13 percent showed any clinical signs of active caries. When these children ate candy in unrestricted amounts, no other dietary change being made, 44 percent showed active caries in five months, and in saliva of 80 percent there were increased counts of L. acidophilus.
References: numerous in leading dental, medical and scientific journals since 1925 ; a few on the main line through these publications follow—J. Den. Res., 1933 ; J. Am. Den. Assoc., 1933, 1936; J. Nutr., 1934.