Flossing, combined with tooth and tongue brushing, significantly reduces the amount of disease-causing bacteria in the mouth, according to a twin study published in the Journal of Periodontology, the publication of the American Academy of Periodontology.

The study, Treatment outcomes of dental flossing in twins: molecular analysis of the interproximal microflora (J Periodontol 2008; 79: 1426–1433), carried out at New York University, comprised 51 sets of twins between the ages of 12 and 21. Each set was randomly assigned a two-week treatment regime with one twin brushing with a manual toothbrush and toothpaste and the other brushing with a manual toothbrush and toothpaste and flossing. At the end of the two week trial, samples were taken from both pairs of twins and compared for levels of bacteria commonly associated with periodontal disease.

The results showed those twins who did not floss had significantly more bacteria associated with periodontal disease compared to the matching twin who flossed.

Although interproximal cleaning is universally recognised as a primary component of oral hygiene, only a small number of studies have reported on the clinical effectiveness of flossing for plaque removal and the promotion of gingival health, the authors note.

'Our study showed that the combination of tooth and tongue brushing plus flossing had a significant effect on suppressing periodontal and cariogenic pathogens compared to the group that did not floss,' they conclude.

Commenting on the study, Dr Kenneth Kornman, editor of the Journal of Periodontology, said: 'Twins tend to share the same or similar environmental factors such as dietary habits, health and life practices, as well as genetics. In this case the only difference was flossing and the outcome was significant'.

Dr Susan Karabin, president of the American Association of Periodontology, said: 'Patients tend to think that flossing can't possibly make that much of a difference. But this study demonstrates flossing can significantly reduce the amount of periodontal disease causing bacteria, even after just two weeks.'