HUMAN ROOT CARIES - MICROBIOTA OF A LIMITED NUMBER OF ROOT CARIES LESIONS

The microbiota of root caries lesions of different grades of severity were studied. Fourteen lesions were examined. The experimental design of the study allowed correlation of histopathologically distinguishabl e stages with specific and distinct microbial populations. Dentin samp les were ground in a sterile mortar and cultured anaerobically on nons elective Columbia blood agar plates supplemented with 5% hemolyzed hum an blood and on media selective for Lactobacillus spp. and streptococc i. 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. In initial as well as in advanced lesion s gram-positive bacteria accounted for approximately 90% of the CFUt. The proportion of Actinomyces, and in particular A. naeslundii was sig nificantly higher (p<0.05) in initial lesions than in advanced lesions . In contrast, the percentage of Streptococcus and especially S. mutan s was higher (p < 0.05) in advanced than in initial lesions. Surprisin gly low (0.8% of the CFUt) was the percentage of lactobacilli in advan ced lesions. Gram-negative bacteria formed a minor part of the microbi ota in both initial and advanced lesions. Among the gram-negative isol ates, Prevotella, Selenomonas, and Bacteroides spp. were most noticeab le. In advanced lesions, only the outermost layer of 0.5 mm thickness was populated by a high number of bacteria; the following segments har bored a negligible number of bacteria only. It is concluded that root caries is a continuous destruction process which is restricted to a su bsurface zone of limited depth. The necrotic dentin is successively wo rn away, leading to a saucer-shaped cavitation which is repopulated by plaque. The creation of cavitations favors an aciduric flora. This mi ght explain the succession of bacterial populations observed during th e destruction process.