ENZYME INHIBITORS FOR DENTIFRIGES* By R. S. Tufts College Dental School, Boston, Mass. t THE INlvORMATION TO BE presented is concerned with the approaches used by dental investigators in searching for caries-inhibiting agents for dentifrices, a description of the method we employ for primary screening in our search for enzyme inhibitors, and a presentation of examples of one class of inhibitors from a group of several hundred compounds studied. The em- phasis will be on enzyme inhibitors for dentifrices of the future rather than evaluation of the inhibitors in dentifrices that are currently being marketed. It is well known that changes occur gradually among ethical pharmaceu- tical products, where useful drugs are continually being replaced by newer products that are superior in certain respects. The pace of obsolescence be- cause of research is just as rapid for dentifrice inhibitors. It can be pre- dicted as a safe generalization that some of the inhibitors currently used in dentifrices will be replaced by newer and better ones within a few years. Our presentation deals with some of the means which can be used to locate and narrow down the selection of new inhibitors of acid production by dental plaques. Some background regarding the etiology of dental caries might help to explain the current interest in enzyme inhibitors. A skeleton of the theory that is commonly held regarding the cause of dental caries is given in Fig. 1. It presents only those parts of the general theory which I believe are poten- tially useful for the control of dental caries by dentifrice additives, and ex- plains merely the production of corrosion or pitting of tooth enamel. The three general essentials are carbohydrates, a dental plaque, and tooth enamel. Diffusible carbohydrate passes into the dental plaque, which con- sists of an adherent mass of micro6rganisms plus some proteins of saliva, is there converted to acid rapidly enough to cause a localized decalcification of enamel. Once the surface layer of enamel is etched, the lesion progresses rapidly. The goal of most dental investigators is to prevent the original * Presented at the May 14, 1954, Meeting, New York City. • Supported by grants from American Chicle, Beechnut Packing, Colgate-Palmolive, Lam- bert Pharmacal, Lever Brothers, and Procter and Gamble Companies, and the Sugar Research Foundation. 266

ENZYME INHIBITORS FOR DENTIFRICES 267 pitting rather than to arrest dental caries after the smooth enamel surface is destroyed. The various links in this chain of events are sugar, the dental plaque, its organisms, their enzyme systems, acid, and an enamel surface that is sus- ceptible to acid. One approach to the problem would be to keep dental plaques from accumulating on surfaces of teeth. Improvements on oral hygiene can do this, as was shown by Fosdick who found that tooth brushing after meals reduced dental caries (1) either by preventing the plaques from developing or by aiding clearance of sugar from the mouth. The effect that can be achieved in this manner is limited since mechanical cleansing is not apt to affect the inaccessible surfaces of teeth, many of which are most sus- ceptible to dental caries. Carbøh2drate I Den• P• Tooth •1 •• Bac•r• [Ac• • • Figure l. It might be possible to reduce the numbers of organisms in dental plaques. The use of penicillin has been advocated by Zander for controlling the rate of acid formation from dental plaques (2). Other workers question whether a continual use of a broad spectrum antibiotic would be desirable because it might cause development of resistant strains of organisms or produce un- desirable changes in bacterial population in the mouth (3). Another pos- sible way of breaking this chain of events is to produce alkali or buffer that will neutralize the acid as rapidly as it is iBrmed. Dilute solutions of urea act in this manner. The enzyme, urease, is present in dental plaques and converts the urea to ammonia so rapidly that the plaques actually become alkaline (4). The effect with dilute solutions is transient but it is theoreti- cally possible to obtain neutralizing effect for a reasonable period of time by use of an adsorbed buffer. Another approach to the problem involves the protection of enamel by producing a less soluble layer upon its surface. Fluoride has been tried in dentifrices for this purpose (5), stannous fluoride has been proposed (6), tetradecyl amine has been studied (7), and several inorganic substances have been considered (8). It should be possible to find an organic, non- toxic chemical capable of giving a protective layer on enamel, but a prac- tical problem will be how to cause such a substance to penetrate the dental plaques and attach itself to the enamel surface.