CRITICAL EVALUATION OF THE EVIDENCE ON AMMONIUM DENTIFRICE THERAPY* By THOMAS J. HILL, D.D.S. l•estern Reserve University, Cleveland 6, Ohio T•E PURPOSE OF this dis- cussion is to give the viewpoint of an investigator in the field of dental caries but of one whose personal work has not carried him very far into the influence that ammonia may have in the control of this dis- ease. Throughout this discussion it should be very carefully borne in mind that the causative factors in dental caries are only partially understood. It has been pointed out that there is a relationship be- tween the activity of carious lesions and the incidence of Lactobacilli in the mouth. This does not establish Lactobacilli as the sole etiologic factor nor indeed does it prove that it is more than a secondary invader due to the presence of the disease. One may rightfully assume that these organisms play some part as an etiologic agent because they are known acid producers and it is also known that when conditions are created in the oral fluid which materially decrease the ability of Lactobacilli to grow in the mouth, * Presented at the Dec. 8, 1949, Meeting, New York City 73 then those conditions also decrease the activity and the incidence of carious lesions. On the other hand it is recognized that in in vitro experiments other mouth organisms are much more effective in the production of acids than the Lactobacilli and they are found in much greater numbers. For instance, the gamma strepto- cocci will, in in vitro experiments, produce two to three times as much acid as Lactobacilli and their pres- ence in the mouth is counted in millions where Lactobacilli are counted in thousands. Yet the correlation has not been made be- tween the numerical presence of gamma streptococci and the activity of caries. It has been established that low Lactobacilli counts are re- lated to inactivity of caries but there is no demonstrated proportional re- lationship between high counts, that is, there is no demonstrated prop, or- riohal reduction in caries when counts of Lactobacilli are reduced from 300,000 to 100,000. These facts are emphasized be- cause it would appear that the hypothesis of the relationship is in-

74 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS complete and presumptive, and the problem may be far more compli- cated than a simple Lactobacilli- caries relationship. This does not detract from the use of this method which is the best known method available for measuring the activity of caries. However, it does empha- size the importance of clinical ob- servations in addition to such evi- dence as is available from laboratory studies. All ammoniated and ure- ated dentifrices, with or without urease, are primarily based upon their influence on the growth, mul- tiplication, and acid-producing abil- ity of Lactobacilli. A review of the literature reveals some confusion on the relationship of ammonia to caries susceptibility. It would appear that this is largely the result of differences in methods of technical procedure which pro- duced results which were not com- parable. These same difficulties may still be present. Some dif- ferences still arise between the work of different investigators. Stephan's recent work showed no marked inhibitory effect of am- monium phosphate on growth of Lactobacilli, and work at our Uni- versity gives results which are not entirely in keeping with the work of Kesel. It should be said, however, that Kesel's work with ammonium salts are reproducible under the con- ditions which he stipulated. We have not been able to verify Kesel's observation that ,4erobacter aerogenes is inhibitory to Lacto- bacillus acidophilus. In fact the Lactobacillus acidophilus is ex- tremely inhibitory to ,4. aerogenes. If these two organisms are plated to- gether the Lactobacilli completely inhibit the growth of ,4. areogenes. We are, however, able to verify Kesel's demonstration of the in- hibitory influence on Lactobacilli of a tiltrate made from an eight-day culture of,4. aerogenes. It should be noted that such a tiltrate has a final pH of 8.0 which added to media raises the pH sufficiently to in- fluence the growth of Lactobacilli. We have also observed, as he has re- ported, that when Lactobacilli are rapidly reduced in saliva there is a material increase in the ,4. aerogenes in some but not all mouths. We have found this influx of ,4. aero- genes to be a transitory one, and that after a period of a few weeks the incidence of these organisms re- turns. to normal. What part these organisms play in caries resistance would seem open to question. Dr. Sholom Pearlman of our University has studied the influence of ammonia on the growth and re- production of Lactobacilli. In his experience the influence of ammonia was to depress their growth rather than destroy the organisms. He conducted very carefully controlled experiments, using a Warburg res- pirometer with the resultant acids measured by the CO,. formed. When Lactobacilli were suspended in a media held steadily at a pH of 7.4 a decrease was observed in the rate of acid production when ammonium phosphate was added to the glucose mixtures. It was further observed that the