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Every time I go to the dentist, I'm told I need to be flossing more. We always go over the techniques, etc, and I always get a Stern Talking To about not flossing once or twice a day. If I go to the dentist regularly (every 4-6 months), then aren't they cleaning everything out anyway?

Anecdotally, I only got cavities after not going to the dentist for three years, and even then, just two little ones. Prior to that, for 30 years, no cavities, and no flossing.

Here's one example of the claim, from http://www.saveyoursmile.com/healtharticles/flossing.html:

If you do not floss and allow plaque to remain in between teeth it eventually hardens into a substance known as tartar. Unlike plaque which can be easily removed by brushing, tartar can only be removed by your dentist. Over time, levels of more dangerous types of bacteria build up within tartar. Mean and vengeful, these bacteria produce toxins which irritate and inflame the gums. This condition is known as gingivitis. If gingivitis is left untreated it can progress to periodontal disease - a condition where bacteria and their toxins invade not only the gums but also the bones and the structures supporting the teeth. This can lead to bone loss, loose teeth, and teeth which fall out.

However, the scientific articles I can find use small sample sizes (N=4, for http://ukpmc.ac.uk/abstract/MED/6937641, to first establish that flossing reduces bacterial buildup, and N=119 for http://ukpmc.ac.uk/abstract/MED/2786959, taking patients who already have gingivitis to see if flossing helps).

Has there been a large, longitudinal study that compares the effectiveness of flossing to regular dentist visits for plaque reduction and avoidance of gingivitis?

  • If your dentist is saying that you need to be flossing more, it's because in his or her opinion your mouth (teeth and/or gums) is not as healthy as it should be. Also, cleaning your teeth yourself, and visiting the dentist regularly, are not alternative strategies: you're supposed to do both. Flossing can't remove plaque after it has hardened (the dentist can), but it removes soft debris to delay plaque formation. FWIW my dentist gave me tiny brushes (a thin wire with bristles around it) to poke and clean between my teeth: instead of flossing. It's just that a regular toothbrush doesn't reach – ChrisW Apr 1 '12 at 1:17
  • ... the surfaces where the teeth face each other. – ChrisW Apr 1 '12 at 1:19
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    @ChrisW-- They certainly seem like alternative strategies to me, hence the question. I'm looking for something more than just the repeated assertion that flossing is good. – mmr Apr 1 '12 at 18:16
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    @ajax333221-- I brush pretty regularly, but I just don't floss. You do raise an interesting question, though-- maybe some people are more prone to cavities or dental issues, no matter how much dental care they perform or receive. I'd think that that's a separate question. Sorry about your tooth, hope it doesn't hurt much. – mmr Apr 2 '12 at 17:45
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    I've always thought this was contentious too. I personally have never had a cavity and I'm 32 years old. Yet I don't take care of my teeth that well. I only floss when it's necessary to remove a piece of food (like steak, or popcorn). And brushing usually only happens twice a day, but not for the recommended 2 minutes. On the other hand, I know people who flossed daily, and brushed 3 times a day, and have chronic dental problems. I'm aware it's all anecdotal, but I think that genetics or some other factor (nutrition, diet, or perhaps acid reflux) probably pays a much larger role. – Kibbee Sep 7 '12 at 19:43
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I found several small studies looking at (a) the effectiveness of flossing, and (b) the amount of flossing that happens in different groups. However, you seemed to be after larger studies.

I couldn't find any large studies, but what I could find were meta-analyses, where they systematically look for small, high-quality studies and put the data together to get stronger conclusions.


This study looked at the professionally flossed teeth of children. Why?

No flossing trials in adults or under unsupervised conditions could be identified.

They looked at six trials, with 808 children.

Professional flossing performed on school days for 1.7 years on predominantly primary teeth in children was associated with a 40% caries risk reduction.

[...]

Both three-monthly professional flossing for 3 years and self-performed flossing in young adolescents for 2 years did not reduce caries risk.

[...]

Professional flossing in children with low fluoride exposures is highly effective in reducing interproximal caries risk.

They explicitly warn:

These findings should be extrapolated to more typical floss-users with care, since self-flossing has failed to show an effect.

So, regular flossing of children, done right, and done daily seems to help (especially where there is low fluoride - I don't know if that is referring to water, or toothpaste exposure). Other situations are not as clear.


The Cochrane group looked at self-flossing and brushing of adults, versus brushing alone.

They were a little scathing about the studies available: They rated five of the twelve trials they looked at (totalling over 1,000 participants) as "at high risk of bias", and the others they rated as "at unclear risk of bias". Overall, they stated:

Trials were of poor quality and conclusions must be viewed as unreliable.

They explain that:

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.

[...]

None of the included trials reported data for the outcomes of caries, calculus, clinical attachment loss, or quality of life.


Conclusion

Your question basically asked: is there high-quality evidence that long-term self-flossing helps prevent caries and gingivitis?

The answer is: No, there are no high-quality studies found by two teams that were systematically searching for them. Meta-analysis of the smaller studies suggests that are not yet of a high-enough quality to draw a firm conclusion.

In children, it seems a systematic daily flossing by professionals reduces the risk of caries by 40%, but this is clearly not a cost-effective treatment plan.

  • This is very thorough, thanks! Of course, since it matches my impressions, I'm all the more inclined to think that it's right :) But the last Cochrane study I looked at was from @matt_black regarding mammograms (skeptics.stackexchange.com/questions/6473/…). In both cases, the aggregation done by Cochrane showed that the proposed procedure had no positive effect. Do they ever find that a medical procedure is worth it? – mmr May 28 '12 at 15:54
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    Ha! Yes, they do. They tend to look at new or controversial treatments, where the evidence is barely in. We tend to ask questions about doubtful treatments. So, the sampling bias might wrongly suggest medicine has nothing to offer but suggestions on what NOT to do! – Oddthinking May 28 '12 at 22:42
  • Forbes pointed out Furthermore, the children in the study were found to have poor tooth-brushing habits and a low exposure to fluoride — the anion of the element fluorine known to prevent cavities. Thus, the authors noted that the evidence was unable to answer the critical question of whether flossing provides tangible benefits if one is already brushing with a fluoride toothpaste. Does that make your last statement incorrect? – gman Jan 21 '16 at 15:14
  • @gman: The Forbes article shows there has been a third meta-analysis published since I wrote this answer. I haven't read it, but the Forbes article seems to align with the conclusions here - I can't see which statement you think it invalidates. – Oddthinking Jan 21 '16 at 18:39
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    Is there some explanation of why there should be such a marked difference between professional and amateur flossing results? Presumably if it's really flossing, and the results apply to adults, we can all like to floss just like the pros and reap the rewards. – Casey Aug 3 '16 at 21:27

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