have dealt mainly with the indwelling and the plaque sampling/in vitro electrode methods of measuring intra-oral plaque pH, particularly as they relate to changes in pH associated with the ingestion of different foods. Largely omitted has been the role that the antimony touch-type electrode has played in plaque pH measurement and the considerable amount of information it has generated over the approximately 40 years that plaque pH has been measured with electrodes. Also omitted have been major aspects of interpretation of dental plaque pH and its significance. This article, therefore, has attempted to make up for some of these deficiencies.Major studies on plaque pH with the antimony pH electrode.The first significant observation on dental plaque pH was made by Stephan4 in 1940 with a rod type of antimony pH electrode, when he showed that the pH of dental plaque decreases rapidly following a brief glucose or sucrose challenge, and, after reaching a minimum, the pH slowly returns to its starting level. In a subsequent study on 65 caries-active and caries-free individuals carried out over a period of two years, Stephan,5 with the same type of antimony pH micro-electrode, demonstrated that the pH level of the Stephan pH response varied with the level of caries activity; the greater the caries activity, the more acidic the response (Fig. 1). This was seen when maxillary or mandibular labial incisor plaque samples were compared in individuals of different caries activity, and when maxillary and mandibular labial incisor plaque samples were compared within each individual (Fig. 1). Maxillary incisors are teeth in the human dentition that almost invariably show a higher caries incidence than do mandibular incisors (Fig. 2). This fact, plus consistent plaque pH differences (not to mention convenience of access), makes the incisor teeth particularly ideal dentition sites for studying the inverse relationship between the Stephan pH response and dental caries activity first seen by Stephan5 and subsequently confirmed by others.6-9Using a rod type of antimony electrode similar to that of Stephan,4,5 Stralfors demonstrated the existence of an inverse relationship between the number of lactobacilli in saliva (often used in earlier years as an index of caries activity) and the minimum pH of the Stephan response.Recently, Edgar et al.,10 by the plaque sampling method, observed a similar relationship between S. mutans in plaque and the acidicity of the Stephan challenge. Consistent with both studies was the observation of Denepitiya and Kleinberg11 that S. mutans and lactobacilli are present in higher numbers in maxillary than in mandibular incisor plaque samples. It needs to be kept in mind, however, that, although both organisms show an association with caries activity and with the plaque pH, their frequent absence from caries-active plaque25 samples and their usual presYork, Stony Brook, New York 11794; and *Department of Oral Physioloence in low numbers in these plaque samples clearly indicate that, alone, they cannot be resp...
