Profiling of Dental Plaque Microflora of Root-Caries Lesions

Objectives: Not only decalcification of root surface but also degeneration of dentinal protein such as collagen is thought to be related to root-caries progression. This study aimed to profile plaque microflora of root-caries lesions, and to examine the proteolytic activity of these bacteria.

Methods: Six subjects (24-73 year-old; mean age 57) with root-caries were investigated. After informed consent was obtained, plaque samples on root-caries lesions (R), as well as healthy supragingival plaque (S) and subgingival plaque of periodontitis (P), were collected. Each sample was cultured anaerobically on CDC blood agar plates. The isolated bacteria were identified by 16S rRNA sequencing analysis and examined for proteolytic activity using skim-milk agar plates.

Results: The mean bacterial numbers (logCFU/mg) of plaque samples were 7.4±0.4, 8.0±0.4, 7.1±0.7, from R, S and P, respectively. Propionibacterium (43 out of 151 strains), Actinomyces (37 stranis), Lactobacillus (14 strains) and Streptococcus (13 strains) were predominant in R, while Actinomyces (43 strains out of 116 strains) and Streptococcus (19 strains) were predominant in S. Actinomyces (36 strains out of 99 strains) and Prevotella (18 strains) were predominant in P. The proportions of proteolytic bacteria were 39.9%, 26.1% and 63.4% from R, S and P, respectively. Among 68 proteolytic isolates from R, Actinomyces (28 strains), Lactobacillus (9 strains), Bifidobacterium (8 strains) and Streptococcus (8 strains) were predominant.

Conclusions: The composition of plaque microflora of R was distinct from those of S and P. These results suggest that specific plaque microflora is formed in R, and that proteolytic bacteria, belonging to Actinomyces, Lactobacillus, Bifidobacterium and Streptococcus, are related to root-caries through degradation of dentinal protein. Supported by Tohoku University Graduate School of Dentistry Young Dental Researchers Encouragement Program in 2007-2008.