Relationship among mutans streptococci, "low-pH" bacteria, and lodophilic polysaccharide-producing bacteria in dental plaque and early enamel caries in humans.

Multiple interactions occur among major determinants of dental caries. We have studied the bacterial flora and pH-lowering capacity of the same dental plaques in relation to caries. The findings on the plaque flora are reported here. The buccal surfaces of upper teeth in each subject were selected for study. A low-caries group had no "white spot" caries (ws) in the selected dentition area; a higher-caries group averaged 4.1 ws in this area. The latter group was divided into subjects with 2, 3, or 4 ws and subjects with 5, 6, or 7 ws. Enumerated organisms in plaque samples (sound and ws sites) from all subjects were: (1) mutans streptococci (MS) on mitis-salivarius-bacitracin and mitis-salivarius agar; (2) non-mutans streptococci (non-MS) on mitis-salivarius agar; (3) organisms that were categorized according to their minimum pH in sugar broth, i.e., the predominant undifferentiated total flora on blood agar or the predominant non-MS flora on mitis-salivarius agar; and (4) iodophilic polysaccharide-storing organisms on trypticase-yeast extract-salts agar. Plaques covering ws lesions contained generally only low proportions (< 0.1%) of MS. The plaque proportions of all the above 4 bacterial groups were increased in the higher-caries group but were similar for s and ws sites in this group. Over half of the total plaque flora in subjects with 5, 6, or 7 ws consisted of "low-pH"-type organisms (minimum pH < 4.4). Many of these were neither MS nor "low-pH" non-MS. The numerical emergence of MS in plaque appeared to be preceded often by other types of "low-pH" bacteria, including the non-MS. Caries development in the absence or presence of MS as well as different bacterial successions in plaque can be explained readily by the dynamic and positive relationship among the factors carbohydrate consumption, plaque flora composition, plaque acidogenic potential, and caries activity.