Laboratory Evaluation of Potential Caries-Preventive Agents in Dentifrices* By S. D. GERSUON, O. W. NEIDITCH and D. J. MARTIN Lever Brothers Company Research and Development Division, Edgewater, N. •. DENTAL CARIES OR tooth decay has been defined as a disease of the calcified tissues of the teeth caused by acids which are formed by the action of microSrganisms on carbohydrates. It is characterized by a decalcification of the inorganic portion of the tooth and is accompanied or followed by a disintegration of the organic substance (1). Though most investigators agree that the carious process is initiated by an acid decalcifi- cation of the enamel, some maintain that the first step in the disintegration of the enamel involves a splitting of the organic portion of the tooth enamel by proteolysis (2, 3). Others maintain that chelation rather than acid attack is responsible for decalcification of the inorganic portion of the tooth (4, 5). Regardless of the mechanism, investigators agree that micro- organisms are essential to the carious process. It is generally accepted that dental caries begin on the surfaces of teeth. Since the carious lesion begins in a relatively small circumscribed area, bacteria must be localized, in part by a bacterial plaque, and held in close contact with enamel before the lesion, called dental caries, is produced. It is natural, therefore, that removal of these bacterial plaques as well as mechanical removal of the bacterial media can be considered a method of caries control (1). Dentifrices are preparations intended for use with a toothbrush for the purpose of cleansing the accessible surfaces of the teeth (6). In addition to enhancing personal appearance by maintaining cleaner teeth (7-10), brushing with a dentifrice reduces the incidence of tooth decay (11), helps maintain healthy gingiva (12, 13) and reduces the intensity of mouth odors (14, 15). During the past decade, considerable research effort has been expended in an attempt to develop dentifrices capable of effecting greater reductions in the incidence of tooth decay than possible with a tooth cleansing denti- * Presented at the May 18, 1956, Meeting, New York City. 434

CARIES-PREVENTIVE AGENTS IN DENTIFRICES 435 frice. Such dentifrices, referred to as "therapeutic dentifrices," have been defined as "tooth cleaning agents which have incorporated in them some drug or chemical which by reason of its bactericidal, bacteriostatic, enzyme- inhibiting or acid-neutralizing qualities, reduce the incidence of dental caries or aid in the control of periodontal disease" (16). Though several compounds have been reported to effect at least one of the objectives of a "therapeutic dentifrice," there is no general agreement, because of con- flicting or inconclusive evidence, that any of the compounds contributes to dental health beyond that obtained with a well-formulated cleansing denti- frice. The ultimate criterion of effectiveness of a cleansing or therapeutic dentifrice in reducing the incidence of caries is a result of a controlled clinical study. Because of the cost and length of time required to conduct such evaluations, several laboratory tests have been suggested for use in predicting the anticaries effectiveness of a potential caries preventive agent. These tests have been studied and evaluated (17) with the recommendation that the results of laboratory tests for caries-susceptibility should not be used as the sole criterion for determining the ability of therapeutic agents to limit tooth decay and that the development of an accurate caries-suscepti- bility test should be a major objective of dental investigators. This paper is concerned with the in vitro laboratory evaluation of potential caries-preventive agents intended for use in a dentifrice. The evaluation procedure utilized is based on the most generally accepted cause of tooth decay, i.e., acid decalcification of the calcified tissues of the teeth. Most dentifrices contain substances that effectively block acid formation in in vitro saliva-sugar mixtures (18). The old chalk-soap as well as modern insoluble phosphate-synthetic detergent dentifrices are effective in such tests primarily due to the presence of a surface active agent and flavor. It is believed that such dentifrices do not have anticaries effectiveness beyond that contributed by the cleansing effect. While numerous compounds have been found to prevent or reduce the formation of acids from sugars by oral micro6rganisms, it is necessary for effective anticaries activity for these materials to be present at the site of acid formation, i.e., the plaque, whenever fermentable carbohydrates are brought in contact with the plaque. Fosdick (19) pointed out that "if compounds could be found that would adsorb, or otherwise attach themselves to the plaque, and at the same time be powerful enzyme inhibitors either in situ or by being gradually released from the plaque, these compounds could be incorporated into an effective therapeutic mouth wash or dentifrice." "Under these conditions the active ingredient would become attached to that portion of the dental plaque that remains after the teeth are brushed which by coincidence is, in the main, that under which dental caries normally occurs" (l 8).