A 2019 Cochrane review10 on home-use of interdental cleaning devices in addition to toothbrushing for preventing or controlling periodontal disease or dental caries found no randomized, controlled trials assessing effect on interproximal caries and very few studies evaluating periodontitis. The authors found that use of floss or interdental brushes in addition to toothbrushing may reduce gingivitis or plaque, or both, more than toothbrushing alone and that interdental brushes may be more effective than floss.10 Available evidence for tooth-cleaning sticks and oral irrigators was reported to be limited and inconsistent. Outcomes were mostly measured in the short term (i.e., 1 to 3 months) and participants in most studies had a low level of baseline gingival inflammation. Overall, the evidence was graded as low to very low-certainty, and the effect sizes observed may not be clinically important. The authors recommended that future trials report participant periodontal status according to the new periodontal diseases classification, and last long enough to measure outcomes for interproximal caries and periodontitis.10
A 2011 Cochrane systematic review evaluating the evidence for the impact of flossing on managing gingivitis11 found that by the standards of the GRADE Working Group, the evidence on this question was of very low quality, due to uncertainty about the estimate because of the small number of studies, sample sizes, and some concerns regarding interpretation of the results. With these caveats and limitations in mind, the summary of results of these short-term (i.e., up to 6 months of follow-up) investigations were that when flossing was added to toothbrushing, there was a statistically significant, albeit clinically small, reduction in the measures of gingivitis.11 An earlier meta-analysis by Berchier et al.12 explored the impact of adding flossing to brushing on indices of plaque and gingival health and failed to find statistically significant improvement. They nonetheless concluded that a first consideration ought to be whether high-quality flossing is an achievable goal.
A meta-analysis of studies examining the impact of flossing on interproximal caries13 found that regular (5 days per week) professional flossing resulted in a statistically significant reduction in interproximal caries, a result that was not seen with intermittent (every 3 months) professional flossing nor self-flossing.