The Effect of 2-Methyl-1,4-Naphthoquinone on the Incidence of Dental Caries

Abstract

In 1943 it was suggested that the production of dental caries depends upon first, the rate of acid formation in the mouth, and second, the rate of neutralization of acid in the regions associated with the caries susceptible portions of the teeth (1). On this basis dental caries should be retarded by a decrease in the rate of acid formation or an increase in the rate of acid neutralization. Most of the successful methods of controlling caries have worked by decreasing the rate of acid formation. This is natural, because the rate of acid neutralization is controlled by many factors which at present cannot be materially changed (1). Probably the most successful experimental control of the rate of acid formation, with subsequent decrease in caries activity, has been accomplished by the reduction of fermentable sugars and carbohydrates in the diet (2, 3, 4), or by their elimination from the mouth through oral hygiene (5). These methods of caries control, however, depend entirely upon the cooperation of the patient. This cooperation cannot be expected of large masses of population. Another way of reducing the rate of acid formation is by interfering with the enzyme or co-enzyme systems which are necessary for acid production. Several agents may be used, some of which have been tried experimentally and some clinically. Iodoacetic acid has been tried experimentally with rats (6). It is probably too toxic for human use. A 30% urea solution (7), used as a mouthwash, acts as a protein denaturant, destroying the enzymes and hence preventing acid formation. A urea quinine mouth rinse has also proved successful (8). Ammoniacal silver nitrate reduced on the susceptible surfaces of the teeth leaves a deposit of colloidal metal which presumably retards fermentation (9). The enzyme inhibitor which has had the most wide-spread study and experimental use is the fluoride ion (10). This ion inhibits the hydrolysis of phosphoric esters and hence retards acid formation. Furthermore, the fluoride ion is absorbed by the dental enamel, forming a compound less soluble than unchanged enamel. Probably both actions are responsible for the success of fluorides in controlling or preventing caries. In 1942 (11, 12), it was found that synthetic vitaminK (2-methyl-1 ,4-naphthoquinone), when added in minute quantities to saliva-glucose mixtures, in vitro, would prevent the formation of significant amounts of acid. There was no evidence that its action as an enzyme inhibitor was closely associated with the vitamin activity. Preliminary experiments indicated that the material would