This is an excellent and particularly detailed systematic review of the effect of flossing on interproximal caries. The conclusions are precisely delineated and supported by the evidence. The authors are to be commended on their discussion section, in which they explore the limitations of the results and their implications in terms of research and dental practice. They draw attention to a number of issues, including the lack of anticaries effect seen in self-flossing studies and the potential positive and negative effects on caries of different flossing techniques. They raise the point that the current evidence is unable to answer the question of whether flossing provides a benefit above and beyond brushing with a fluoride toothpaste.

The authors conclude that the current level of evidence is consistent with the hypothesis that regular and meticulous flossing can drastically lower interproximal caries risk in young children who have poor toothbrushing habits and low fluoride exposure.

The evidence-based approach is nested in reductionist science and a corollary to this rigorous paper is: can such methodology cope with a process involving interdependent variables? In this particular case the complexity of the inter-relationship of flossing and fluoride in caries development may be difficult, if not impossible, to delineate. For example, will efficient daily removal of interproximal plaque reduce the anticaries effect of fluoride by attenuating (or even eliminating) the ‘fluoride-reservoir’ effect of the biofilm? The two effects are inter-related and one cannot vary the one without influencing the effect of the other.

Studies investigating the anticaries effects of combinations of professional cleaning (including flossing) and topical fluorides were quite correctly excluded, considering this systematic review's methodology. In the real world, however, the combination of those two factors is what occurs: everyone who flosses their teeth effectively also uses fluoride toothpaste. Although the authors suggest that studies embedding factorial designs may provide the answers to determining what fraction, if any, of interproximal caries can be prevented by dental floss in a fluoridated world, such studies may require more complex analytical tools than are currently available. It may be impossible to answer that question and, in any case, it may be irrelevant, since, in the real world, flossing is inextricably intertwined with brushing using fluoride toothpaste. Thus, rather than determining the role of flossing per se, it may be more appropriate to try to determine through an RCT if there is any positive or negative impact (on the anti-caries benefit from brushing with a fluoride toothpaste) of a combination of flossing and brushing (with a fluoride toothpaste).

Practice point

Regular flossing of children's teeth by a trained adult can dramatically reduce interproximal caries in those at high risk of caries.