Human root caries: microbiota in plaque covering sound, carious and arrested carious root surfaces.

The plaque microbiota covering sound or carious root surfaces were studied and compared with that covering arrested root caries lesions. From each of these categories five extracted teeth were examined. The experimental design of the study allowed us to relate the qualitative and quantitative microbial composition to the degree of integrity of the root surface. Plaque was sampled by a newly developed 'mowing' technique. Plaque samples were cultured anaerobically on nonselective Columbia blood agar plates supplemented with 5% hemolyzed human blood and on media selective for Lactobacillus spp. and streptococci of the mutans group. The cultivable microbiota were quantitatively speciated using Rapid ID 32A, Rapid ID 32 Strep, API 20 Strep, API ZYM, and API 50 CH tests and SDS-PAG electrophoresis. Regardless of the state of mineralization, the microbiota on all surfaces resembled marginal plaque associated with gingivitis. In addition to the gram-positive predominant facultative anaerobic genera Streptococcus, Staphylococcus, Lactobacillus and Actinomyces, gram-negative anaerobes, predominantly Bacteroides, Prevotella, Selenomonas, Fusobacterium, Leptotrichia, and Capnocytophaga, showed the highest isolation frequencies. On all surfaces Actinomyces spp. predominated, with streptococci and lactobacilli forming a minor part of the microbiota. With respect to the detected proportions of anaerobes, microaerophiles, Actinomyces naeslundii, Prevotella buccae and Selenomonas dianae, significant differences were observed between the three categories of root surfaces. The total CFU's on both caries-free and caries-active surfaces were significantly higher than on arrested lesions. In general, the results support a polymicrobial etiology for caries initiation on root surfaces, with A. naeslundii, Capnocytophaga spp., and Prevotella spp. making specific contributions to the processes of cementum and dentin breakdown.