16S rRNA analysis of proximal dental plaque bacteria reveals that daily use of commercialized disposable dental floss Itoyoji® in addition to appropriate tooth brushing slightly gives influence on the bacterial composition

Dental flossing is a widely accepted method to remove food debris and dental plaque from the space between adjacent teeth expecting the protection of teeth and periodontal tissues from the dental plaque associated diseases such as dental caries, gingivitis or periodontitis. But the preventive effect of dental flossing has not been proven with sufficient scientific evidences. In this study, we attempted to observe how the dental flossing in a daily oral hygiene routine gives influence on the bacterial composition of dental plaque by means of 16S rRNA analysis. Fifteen generally and periodontally healthy volunteers without any problems in their oral cavities were carefully selected and then they were strictly commanded to perform tooth brushing after every meal and before sleeping (4 ×/Day) without dental flossing for two weeks and with dental flossing for next two weeks. Dental plaque samples were collected from a proximal area of adjacent teeth as an individually selected fixed observation point at every two weeks. Genomic DNA was extracted from the plaque samples. The V4 region of the bacterial 16S rRNA gene was amplified and sequenced using MiSeq high-throughput sequencing platform to establish the bacterial profile. Sequencing data were analyzed using QIIME. The regular dental flossing for two weeks changed the bacterial composition in the proximal plaque slightly. At a phylum level, Actinobacteria, Firmicutes and Proteobacteria expanded their proportion. On the other hand, Bacteroidetes and Fusobacteria were decreased. Proportions of a few abundant genera fluctuated regularly. Streptococcus and Rothia increased after the dental flossing and decreased when the participant temporarily stopped flossing. This phenomenon was observed in two third of the participants. Regarding the Gram positive to Gram negative bacterial ratio in proximal dental plaque, two weeks application of dental flossing increased the proportion of Gram-positive bacteria in two third of participants. Our data suggests a possibility that the regular dental flossing in addition to appropriate tooth brushing might give influence on the bacterial composition and the balance between Gram-positive and Gram-negative bacteria in the dental plaque at a proximal area of adjacent teeth.