284 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS absorbed on the interface of the crystals. It is quite probable that both phenomena occur. These crystals are concentrated in the enamel rods which are almost purely inorganic. Around the periphery of the rods the cementing substance or organic matrix is dispersed. It is thought that tl• inorganic portion of this material is the same as the inorganic portion of the rod. However, it is highly contaminated with organic material, probably keratin, and hence is not so dense as the interior of the rods. If the apatite were pure, it would be converted to a soluble form, the di- or monophosphate at a pH of 5.2 (3). In so far as it is not pure, the solubility is modified depending upon the amount and type of other ions present (4). The ions such as carbonate, sodium, potassium and mag- nesium, have a tendency to increase the solubility. Ions such as fluoride tend to replace the hydroxyl group, and are bound more firmly so that enamel that has been treated with fluorides dissolves at a pH around 4.5, as contrasted with normal enamel which starts to dissolve at pH 5.2-5.6 (5). DENTAL PLAQUE The tooth in its normal environment tends to accumulate an organic coating. This coating, called the dental plaque (6-9), occurs in rather heavy masses on those surfaces of the tooth that are not normally cleansed by the act of mastication. It is about 70 to 80 per cent living and dead micro&rganisms contaminated with denaturized mucin, desquamated epi- thelial cells and various debris. It is primarily the micro6rganism con- tent of the plaque that furnishes the enzyme system for the glycolysis of sugars. The enzyme systems present presumably are a function of the type of organisms present. In caries active individuals the predominant plaque organisms are acidogenic. This is not true with caries immune individuals. The dental plaque can be readily removed by the usual oral hygiene pro- cedures when it is freshly deposited, but when permitted to accumulate it is held very tenaciously to the surface. Under ordinary circumstances, the plaques are removed by the normal brushing techniques from all of the readily accessible surfaces, but in those areas where dental caries normally occur tooth brushing does not remove the plaques. Hence it may be said that the normal tooth brushing procedures clean all the surfaces except those where caries are most likely to occur. The old slogan, a clean tooth will not decay, is probably correct, but it is impossible to clean those sur- faces where decay normally occurs by normal dental hygiene procedures. It is presumed that when sugars are taken into the mouth they penetrate the plaque and that portion of the acid that f•orms under the plaque on the tooth surface is protected by the plaque. The acids thus confined grad- ually penetrate and dissolve the tooth. It has been fully established that when sugars are placed upon caries active plaques in situ, acid potentials below pH 5.0 are fi'equently found from five to ten minutes after the appli-

DENTAL CARIES CONTROL WITH DENTIFRICES AND MOUTH WASHES 285 cation of the sugar (10). The dental plaques in caries immune cases do not rapidly ferment sugars (11, 12). THE CONTROL OF DENTAI. CARIES On the basis of the above, it is obvious that if the acid decalcification is the cause of dental caries, one should be able to control dental caries by simply preventing the formation of acid or by making the tooth more re- sistant to the effects of acid. Today, every method of caries control that has been effective has utilized one of the above methods. The restriction of dietary sugars prevents dental caries very nicely (13, 14). This method prevents the formation of acid by eliminating all substances from the mouth that may form acids. A similar process has been very effective in animals. Concentrated sugar diets when fed to animals in the normal manner will produce rampant caries (15). When this same diet is given by stomach tube, no dental caries results (16). The use of enzyme inhibitors which will prevent acid formation has also been found effective in the control of both animal and human caries (17, 18). Certain antibiotics that destroy the microbial flora have also been successful in the prevention of dental caries (19-21). The ingestion of fluoride in drinking water or the topical application of fluorides render the tooth more resistant to acids. Both of these methods have been found effective in control of dental caries (22, 23). SOME FACTORS CONTRARY TO THEORY Even though it has been definitely shown that the prevention of acid formation in the plaque and the decrease in solubility in enamel will defi- nitely decrease caries activity in humans and animals, there are a number of factors that have been observed which do not conform to the theory. It has been demonstrated that when refined sugar is made available to a population, dental caries increases materially. On this basis it is thought that natural sugars are not particularly cariogenic while refined sugars are. It is known that fruits and fruit juices generally contain around 10 per cent sugar. The sugar is generally sucrose, the same sugar that is most widely ingested in the refined form. Fruits and fruit juices are not ordinarily considered cariogenic even though they do contain considerable quantities of fermentable sugar. If fermentable sugar is the cause of dental caries, why then does the simple act of refining it make it cariogenic? It is not changed chemically. Furthermore, in most fruits and fruit juices certain vitamins and minerals which act essentially as co-enzymes or activators for the glycolytic enzymes are present, thus making fruit juices more sus- ceptible to fermentation, than pure sugar solutions. On this basis fruit juices should be much more cariogenic than refined sugars, for without the activators, no fermentation occurs. There must be some explanation for this paradox.