Quantitative analysis of the effects of brushing, flossing, and mouthrinsing on supragingival and subgingival plaque microbiota: 12-week clinical trialOriginal paper
Karen Pendergrass is a microbiome researcher specializing in microbiome-targeted interventions (MBTIs). She systematically analyzes scientific literature to identify microbial patterns, develop hypotheses, and validate interventions. As the founder of the Microbiome Signatures Database, she bridges microbiome research with clinical practice. In 2012, based on her own investigative research, she became the first documented case of FMT for Celiac Disease, four years before the first published case study.
Read MoreWhat was studied?
This randomized controlled trial tested how brushing, flossing, and essential oil mouthrinsing affect the dental plaque microbiome over 12 weeks. It compared mechanical versus chemotherapeutic plaque control. Supragingival plaque was profiled by shallow shotgun metagenomic sequencing. A DNA spike-in enabled absolute bacterial quantification in calculated microbial units. Viability PCR measured live bacteria in supragingival and subgingival plaque. Five arms were compared: brushing only, brushing plus flossing, and three groups adding Listerine essential oil rinses.
Who was studied?
Subjects were 300 generally healthy adults enrolled at a single site in Fort Wayne, Indiana. Of these, 256 had gingivitis and were randomized into five arms, and 30 periodontally healthy adults formed a baseline reference group. Mean age was about 43 years in the gingivitis groups. Most participants were female, Caucasian, and non-smokers. The trial was examiner-blind, virtually supervised, and 286 subjects completed it. Plaque was sampled at baseline and after 4 and 12 weeks.
What were the most important findings?
Adding floss to brushing produced no significant change in plaque diversity, richness, or total bacterial abundance versus brushing alone. Only 11 commensal species rose modestly after 12 weeks. Essential oil rinses cut Shannon diversity, species richness, and total bacteria. Versus flossing, the alcohol rinse reduced gingivitis-associated species by 93.6% at 4 weeks and 91.3% at 12 weeks, and malodor species by 88.5% and 85.2%. Viability PCR confirmed these effects and showed subgingival benefit mainly for the combined floss-plus-rinse group.
What are the greatest implications of this study?
The results indicate essential oil mouthrinses provide sustained, superior control of supragingival plaque compared with flossing added to brushing. Regrowth after rinsing was enriched in commensal species rather than gingivitis-associated ones. Below the gingival margin, mechanical flossing combined with rinsing showed synergy, suggesting flossing may help rinses reach subgingival plaque. This positions rinsing as a valuable regimen component. The trial was industry-conducted and focused on plaque microbiology, so clinical gingivitis endpoints and generalizability beyond this population warrant consideration.