Treatment Outcomes of Dental Flossing in Twins: Molecular Analysis of the Interproximal Microflora Patricia M.A. Corby,* Aaron Biesbrock, † Robert Bartizek, † Andrea L. Corby, ‡ Robin Monteverde, § Rafael Ceschin, § and Walter A. Bretz* Background: The purpose of this study was to assess the ef- fects of dental flossing on the microbial composition of inter- proximal plaque samples in matched twins. Methods: The study was a two-treatment, examiner-masked, randomized, parallel-group, controlled study. Fifty-one twin pairs between 12 and 21 years of age were randomized to a 2-week supervised and unsupervised treatment regimen consisting of tongue brushing and toothbrushing or tongue brushing and toothbrushing plus flossing. The reverse- capture checkerboard hybridization assay was used to assess levels (abundance) of 26 microbial species in interproximal plaque samples collected from six sites per subject. An inte- grative computational predictive model estimated average changes in microbial abundance patterns of selected bacte- rial species from baseline to 2 weeks by comparing treat- ment groups. Results: After the 2-week study period, putative periodon- tal pathogens and cariogenic bacteria were overabundant in the group that did not floss compared to the group that performed flossing. Those included Treponema denticola, Porphyromonas gingivalis, Tannerella forsythia (previously T. forsythensis), Prevotella intermedia, Aggregatibacter acti- nomycetemcomitans (previously Actinobacillus actinomyce- temcomitans), and Streptococcus mutans. Microbial species that are not consistent with the development of periodontal disease or dental caries were overabundant in the group that did floss compared to the non-flossing group. Conclusion: In a well-matched twin cohort, tooth and tongue brushing plus flossing significantly decreased the abundance of microbial species associated with periodontal disease and dental caries after a 2-week program. J Periodontol 2008;79: 1426-1433. KEY WORDS Clinical trial; microbiology; twins. T he importance of interproximal plaque control for overall gingival health is well recognized by the dental profession. At the Second Euro- pean Workshop on Mechanical Plaque Control, 94% of participating oral health professionals believed that interproxi- mal cleaning was an essential compo- nent of oral hygiene. 1 Dental flossing is one of the most prescribed regimens by dentists to their patients to disrupt and remove interproximal dental plaque bio- films. Although biofilms cannot be com- pletely eliminated, effective practices of oral hygiene that include daily tooth- brushing, flossing, and rinsing with an antimicrobial mouthrinse can reduce the bacterial load that allows for harmful microbial communities to develop. This approach might be effective because it disturbs the development of pathogenic microbial communities, allowing a more stable and health-associated microbial flora to prevail. Although interproximal cleaning is universally recognized as a primary component of oral hygiene, only a small number of studies have reported on the clinical effectiveness of flossing for pla- que removal and the promotion of gin- gival health. Collectively, these data support that dental floss reduces gingival bleeding dramatically when used regu- larly. In one study, 2 unsupervised floss- ers reduced their gingival bleeding by 38% after 2 weeks of flossing. In another * Departments of Periodontics and Cariology, New York University College of Dentistry, New York, NY. † Procter & Gamble, Cincinnati, OH. ‡ Twins Institute for Genetics Research, Montes Claros, Minas Gerais, Brazil. § School of Arts and Sciences, University of Pittsburgh, Pittsburgh, PA. doi: 10.1902/jop.2008.070585 Volume 79 • Number 8 1426