Monaz: Hello, I'm Monaz Mehta, editor in the Cochrane Editorial and Methods department. Many people use toothbrushes to remove the plaque that builds up on the surface of teeth, but what about getting to the plaque between the teeth? Should we be using dental floss or interdental brushes to help? The relevant Cochrane Review was published in April 2019 and we asked the lead author, Helen Worthington from Cochrane Oral Health at the University of Manchester in England to let us know the answer.

Helen: To keep our mouths and teeth in good health depends a lot on removing the dental plaque that builds up every day and, as Monaz said, most people use toothbrushes to do this. But toothbrushes can’t reach in-between teeth, which is where periodontal (or gum) diseases start and develop, and that’s where dental floss and interdental brushes might help. We’ve examined whether using these interdental aids helps prevent or reduce gum disease, plaque and tooth decay, and have found some, albeit low quality, evidence that they do.
There were quite a lot of studies. We identified 35 randomised trials, with nearly 4000 adult patients, and these found no severe adverse events caused by the devices. Floss was tested most. Its use alongside toothbrushing was compared to toothbrushing alone in 15 trials, to interdental brushes in 9 trials, and to oral irrigators in 5 trials. Floss was also compared to interdental brushes and cleaning sticks, which were made of wood or rubber or elastomer. These devices were also compared with toothbrushing alone and another comparison was between rubber or elastomeric cleaning sticks and interdental brushes. 
None of the trials looked at decay on the surfaces between the teeth, and most did not assess periodontitis, a form of severe gum disease. Gingivitis (which includes redness, swelling and bleeding of the gums) and plaque were widely measured but often using different scales. This makes the results difficult to interpret, especially because it’s not known how much difference on these scales actually matters.
Taking all this together, we can conclude that there is low-quality evidence that flossing, interdental brushes, and oral irrigators may reduce gingivitis. There is also very low-quality evidence that interdental brushes, and cleaning sticks made of rubber or elastomer may reduce plaque. When we compared different interdental devices against each other, interdental brushes and oral irrigators seemed to come out better than floss for reducing gingivitis, but this is once again based on low to very low-quality evidence.
In summary, using floss or interdental brushes as well as a toothbrush may reduce gingivitis, plaque or both, more than toothbrushing alone, and interdental brushes may be more effective than floss. But we only have low or even very low certainty in the evidence that underpins these findings, and we don’t know if the effects are large enough to be clinically important. If these shortcomings are to be overcome, future studies need to address some of the problems in the existing studies. Outcomes need to be measured over a longer time period, and studies should include participants with a broader range of levels of baseline gingival inflammation. 
The take home message is that, unfortunately, the current evidence can’t really tell us if it is worth using these devices to prevent or control periodontal diseases or tooth decay. However, with their relatively low cost and no evidence of important side effects, you may have little to lose by giving them a try. If nothing else, they might help you to take more care over brushing your teeth – and we do know for sure that that will improve your oral health.

Monaz: If you would like to find out more about the different interdental devices and their effects, and to watch for any updates to this Cochrane reviews if more studies are done, just go online to Cochrane Library dot com. A simple search for ‘interdental cleaning devices’ will bring the review to the top of the list.