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  • Title: The final pH of bacteria comprising the predominant flora on sound and carious human root and enamel surfaces.
    Author: van Houte J, Lopman J, Kent R.
    Journal: J Dent Res; 1996 Apr; 75(4):1008-14. PubMed ID: 8708129.
    Abstract:
    Acidogenesis at low pH appears to be an important bacterial cariogenic trait. However, most information in this regard pertains to only a few of the acidogenic dental plaque bacteria. Therefore, the 'final' pH in sugar broth was determined for a wide variety of oral bacteria. Their source was: (1) carious material from advanced root lesions (ARL), (2) plaque from sound root surfaces of root-caries-free subjects (SRS), (3) plaque from "white spot" coronal lesions and sound coronal surfaces of caries-active subjects, and (4) plaque from sound coronal surfaces of caries-free subjects. Strains from groups 1 and 2 (ARL, 389 strains; SRS, 358 strains) were previously identified (van Houte et al., 1994) to the genus/species level and belonged to the predominant cultivable flora (PCF). Strains from groups 3 and 4 also belonged to the PCF but were not identified. All strains were placed in one of 4 final pH categories: < 4.2, 4.2-4.4, 4.4-4.6, and > or = 4.6. The main findings were: (1) ARL samples contained many strains with a final pH < 4.2 (mean percentage of 25.7). They included all strains of Lactobacillus and mutans streptococci (MS), most Bifidobacterium strains and non-mutans streptococci (non-MS), and about 20% of the Actinomyces strains. By contrast, SRS samples contained far fewer strains with a final pH < 4.2 (mean percentage of 8.4) which were nearly all non-MS. (2) Organisms with a final pH < 4.4 constituted mean percentages of 41.5 and 32.1 for the ARL and SRS samples, respectively. (3) The final pH distribution of strains in samples from coronal surfaces showed a tendency relative to caries activity (group 3 vs. group 4) similar to that for groups 1 and 2. Our findings further support the concept that increased cariogenic conditions are associated with increased proportions of organisms capable of acidogenesis at a low pH and that this shift involves organisms other than the MS and lactobacilli.
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