Friday, August 12, 2016

Why I'll keep on flossing, thank-you.

You should floss your teeth everyday.

Knowing how much importance I place on evidence, and given the recent media hype spawned by a story by the Associated Press about the paucity of good quality evidence supporting that recommendation, you might be tempted to call me a hypocrite.

But you’d be wrong.

If you’ve been reading this blog, you’d also know that I fully recognize that we most often have to make decisions in the absence of complete or even good information (see here). And besides, as nice as it would be, we don’t need the highest quality evidence - multiple, consistent, well-conducted randomized controlled trials (RCTs) -  to provide a reasonable answer to every question.

So what is the state of the evidence regarding daily flossing? You could find that out for yourself – no media craze required – at the Cochrane Collaboration (which I’ve written about before here) who wrote:
"Twelve trials were included in this review which reported data on two outcomes (dental plaque and gum disease). Trials were of poor quality and conclusions must be viewed as unreliable. The review showed that people who brush and floss regularly have less gum bleeding compared to toothbrushing alone. There was weak, very unreliable evidence of a possible small reduction in plaque. There was no information on other measurements such as tooth decay because the trials were not long enough and detecting early stage decay between teeth is difficult."
And here's what they concluded:
"There is some evidence from twelve studies that flossing in addition to toothbrushing reduces gingivitis compared to toothbrushing alone. There is weak, very unreliable evidence from 10 studies that flossing plus toothbrushing may be associated with a small reduction in plaque at 1 and 3 months. No studies reported the effectiveness of flossing plus toothbrushing for preventing dental caries."
It should be no surprise that there are no randomized trials reporting a reduction in cavities (dental carries) among flossers compared to non-flossers. Such a study would require that large numbers of subjects be randomized and followed for years (since it takes years for carries to develop). Large, long-term studies are costly and labor intensive, and that's why they haven't been done. Who's going to pay millions of dollars to do those studies? Are you willing to cough up some money for the cause?

Perhaps the industry that profits from the manufacture of dental floss should cover the costs, but why would they when the available evidence is enough to reasonably conclude that regular flossing prevents gum disease, which is really enough to recommend it? Even if that's all that it does, you should be flossing. Never mind that there isn't evidence showing that it prevents cavities.

This is an especially important question among people like me with valvular heart disease (VHD). Gum bleeding that permits oral microbes access to the bloodstream is an important cause of infectious endocarditis: a life threatening infection on heart valve tissue. Among the most common causative microbes are oral bacteria that get into the bloodstream by way of gum injury and micro bleeding that occurs throughout regular daily life (1,2).

When I was diagnosed with VHD about 4 years ago, I started flossing every day. Prior to that, I was like Margaret Wente (whose inflammatory piece in the Globe and Mail sparked my desire to write this post), which is to say that I only flossed a day or two before seeing my dentist, and when I did, my gums always bled. But since flossing daily, my gums hardly ever bleed, and haven’t bled at all at my last 2 dental visits. I’m living proof that flossing prevents gingivitis and there is plenty of other anecdotal evidence like mine to add to the already existent and reasonably good higher-quality evidence that it does.

Another widely reported anecdote that I can speak to: despite brushing twice a day, that string used to have quite a smell when I was finished, but after a few weeks in the habit, the foul scent was gone. Preventing bad breath is another terrific reason to floss your teeth daily, don't you think?

Now, one caveat: all of my comments refer to regular (ie. daily) flossing. Intermittently flossing and stopping will likely lead to more gum bleeding because the gingivitis that causes the underlying bleeding just returns in between flossing stints. That could actually be harmful, since everybody is at risk of endocarditis (though not as at high a risk as people with VHD). But other than that, the potential risk of daily flossing is almost certainly astronomically low.

Just as we don’t need a RCT of parachutes for jumping out of airplanes, we also don’t need anymore RCTs of flossing. As tempting as it may be - because I know how unpopular the idea of regular flossing is to most people - you should not mistake an absence of evidence (or a paucity of evidence, in this case) for evidence of absence. I'm sufficiently convinced that daily flossing is having a positive impact on my oral hygiene, and perhaps even to my overall health, and you should be too.

The stakes may not be as high for you as for me, and you may reasonably decide that a reduction in gingivitis is not worth daily flossing for you, which would be fine because you'd be making a decision based upon a reasonable and well-informed interpretation of the evidence. But please, do not make the mistake that Margaret Wente and others in the media have made, which is to conclude, because it's the conclusion that they like and/or that they think their readers will like, that we should all stop flossing because there is evidence that it doesn't do any good.

That would not be fine at all.

1. Lockhart PB, Brennan MT, Sasser HC, Fox PC, Paster BJ, Bahrani-Mougeot FK. Bacteremia associated with toothbrushing and dental extraction. Circulation 2008;117:3118–3125

2. Veloso TR, Amiguet M, Rousson V, Giddey M, Vouillamoz J, Moreillon P, Entenza JM. Induction of experimental endocarditis by continuous low-grade bacteremia mimicking spontaneous bacteremia in humans. Infect Immun2011;79:2006–2011.

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