'Interdental plaque is more prevalent, forms more readily, and is more acidogenic than plaque on the other tooth surfaces in the mouth.1,2 Therefore, interdental cleansing devices are often recommended as an adjunct to personal oral hygiene. In 1815, a dentist from New Orleans introduced a new method to clean between teeth, using silk dental floss.3 With the introduction of a more resilient nylon version by Charles Bass around the time of the Second World War, dental floss became a standard in the preventive regimen to maintain good oral health. Despite this, in many industrialised countries, fewer than one in three report flossing on a daily basis.5 For many, it is a difficult skill to develop, and a challenging behaviour to adopt.

This systematic review by Sambunjak et al. is a thoughtful look at the clinical evidence to support the claim that daily flossing will reduce dental plaque and prevent dental caries, gingivitis and periodontal diseases. An exhaustive search for randomised controlled trials comparing toothbrushing and flossing with toothbrushing alone, was conducted. Two review authors independently assessed risk of bias for the included studies. Meta-analysis was conducted using a random-effects models with standardised mean difference (SMD) as the main effect measure. Heterogeneity was explored. Sensitivity analyses were planned to take into account the effect of bias and of the sources of funding.

Twelve trials (1083 participants) reported on outcomes for gingivitis; data from 10 studies were used in the meta-analysis for plaque reduction. None of the included trials reported data for the reduction in caries, calculus or clinical attachment loss. In terms of reducing gingival inflammation, flossing plus toothbrushing showed a statistically significant benefit compared to toothbrushing alone at the three time points studied. The results were consistent with those at three and six months. Sensitivity analysis excluding studies at high risk of bias did not alter the results in a meaningful way.

Using the GRADE criteria to judge the evidence, studies were determined to be of very low quality. This means we cannot be certain as to the estimate of the effect (from the meta-analysis) of flossing on gingivitis or plaque reduction. None of the studies reported a sample size calculation. None described adequate sequence generation or concealment of the sequence allocation. Thus, seven studies were rated as having an unclear risk of bias and five at high risk of bias. Furthermore, seven studies were sponsored by industry. Two of the five studies that did not disclose sources of funding were both conducted by authors whose affiliations reveal possible or real association with the industry who produced the investigated products. Also, there was concern related to inadequate compliance in many studies and the potential influence of confounders as other possible sources of bias.

Despite the fact that the evidence to support flossing to reduce gingivitis is very low and the evidence to suggest that flossing reduces plaque is unreliable, we must remember that dental diseases are among the most prevalent health conditions. Furthermore, apart from the occasional short-term soft tissue injury, there are no major health risks associated with flossing. As dental professionals we should continue to encourage dental flossing as an important adjunct to oral health self-care, keeping in mind that further research is likely to affect results of future meta-analyses.

Table 1