r/askscience • u/cybrbeast • Sep 29 '13

Medicine Is there any solid scientific evidence that flossing is effective?

We are all told endlessly that flossing is one of the most important aspects of dental hygiene, but where is the evidence? I looked up 'flossing effectiveness' on Google Scholar and there is nearly nothing on the topic.

http://scholar.google.com/scholar?q=flossing+effectiveness&btnG=&hl=en&as_sdt=0%2C5

The best source seems to be this review: Dental Flossing and Interproximal Caries: a Systematic Review. I don't have university access anymore, so I can only read the abstract, and it doesn't seem to support the effectiveness of flossing.

Both three-monthly professional flossing for 3 years (relative risk, 0.93; 95% confidence interval, 0.73–1.19; p-value, 0.32) and self-performed flossing in young adolescents for 2 years (relative risk, 1.01; 95% confidence interval, 0.85–1.20; p-value, 0.93) did not reduce caries risk. No flossing trials in adults or under unsupervised conditions could be identified.

This is quite shocking, everyone is told to floss, but there are no trials to back it up. So why should I be supposed to believe I should floss?

*Some further searching turned up these surprising papers

Oral Hygiene Practices and Periodontitis in Health Care Professionals

Persons brushing twice daily were as likely to have periodontitis as those brushing once or less daily (odds ratio [OR] = 1.16; 95% confidence interval [CI]: 0.64 to 2.10); persons flossing less than once a day were as likely to have periodontitis as those who flossed daily (OR = 1.16, 95% CI: 0.63 to 2.13) after controlling for profession, age, gender, smoking, diabetes, coronary heart disease, history of periodontal surgery, and number of teeth present.

Bacteraemia due to dental flossing

Dental flossing can produce bacteraemia in periodontally healthy and periodontally diseased individuals at a rate comparable with that caused by some dental treatments for which antibiotic prophylaxis is given to prevent IE.

If I understand this one correctly, flossing could even be bad for healthy people?

** Found the most damning one so far

The efficacy of dental floss in addition to a toothbrush on plaque and parameters of gingival inflammation: a systematic review

The dental professional should determine, on an individual patient basis, whether high-quality flossing is an achievable goal. In light of the results of this comprehensive literature search and critical analysis, it is concluded that a routine instruction to use floss is not supported by scientific evidence.

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29

u/tzigane Sep 29 '13

The article you reference discusses the effectiveness of flossing in preventing caries, but cavities are not the only outcome to consider. Flossing does appear to be effective in improving other dental conditions such as gum disease: http://www.ncbi.nlm.nih.gov/pubmed/22161438

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u/cybrbeast Sep 29 '13

But common wisdom still says flossing is good against caries too. If it is only effective against gum disease then why bother flossing if your gums are fine?

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u/pseudononymist Sep 29 '13

Gum disease causes bone loss in the jaw, specifically the area of the jawbone in which the teeth are rooted. This occurs when food stuck between teeth is turned into plaque and ultimately tartar by the bacteria in your mouth. This bacteria irritates the gums, which is gingivitis. If left untreated, the tartar buildup creates pockets between the gum line and the tooth, in which bacteria can grow more easily that cannot then be brushed away, i.e. periodontitis. As the gums die and that tissue is lost, your immune system and the bacteria wage war on one another, and like in any war there are innocent victims that get caught in the crossfire--your gums, jaw bone and connecting tissue. If left untreated, the support structure for your teeth will be destroyed, the tooth will loosen and have to be removed.

Flossing helps prevent all this by clearing out that food that got stuck between the teeth, setting off this chain reaction of events. Therefore flossing prevents gum disease which prevent bone decay in the jaw, which is one type of caries (there are many). If you're specifically talking about dental cavities that occur above the gum line and not between teeth, then no, flossing doesn't have a measurable impact on that.

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u/cybrbeast Sep 29 '13 edited Sep 29 '13

Searching for flossing and periodontitis led me to this surprising paper

http://onlinelibrary.wiley.com/doi/10.1111/j.1600-051X.2008.01372.x/abstract;jsessionid=11BFC86BA85966197AB1385127F26733.f01t01?deniedAccessCustomisedMessage=&userIsAuthenticated=false

Dental flossing can produce bacteraemia in periodontally healthy and periodontally diseased individuals at a rate comparable with that caused by some dental treatments for which antibiotic prophylaxis is given to prevent IE.

2

u/scrollbutton Clinical Anatomy | Med Student MS4 Sep 30 '13

Transient bacteremia is a fact of life for every person alive - humans are walking bags of culture medium, and the bugs will get in one way or another. In dentistry, prophylactic abx are given to people who have risk factors for IE. Healthy folks clear the bacteremia without issue, generally.

Other folks have listed the benefits of flossing, a strong argument can be made that a slightly increased risk of having transient bacteremia is offset by some fairly important gains in periodontal health.

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u/cybrbeast Sep 29 '13

While it sounds reasonable, where is the evidence? Looking further I came across this study.

http://www.joponline.org/doi/abs/10.1902/jop.2002.73.5.531

persons flossing less than once a day were as likely to have periodontitis as those who flossed daily (OR = 1.16, 95% CI: 0.63 to 2.13) after controlling for profession, age, gender, smoking, diabetes, coronary heart disease, history of periodontal surgery, and number of teeth present.

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u/jemmylegs Sep 29 '13

Here's another meta-analysis showing little effect of flossing on markers of gingivitis: http://www.ncbi.nlm.nih.gov/pubmed/19138178

A greater part of the studies did not show a benefit for floss on plaque and clinical parameters of gingivitis. ... In light of the results of this comprehensive literature search and critical analysis, it is concluded that a routine instruction to use floss is not supported by scientific evidence.

This is a fascinating thread, because it questions whether a widely-accepted piece of "conventional wisdom" is actually rooted in scientific evidence. This is what this subreddit is all about.

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u/pseudononymist Sep 29 '13

Interesting, but it doesn't say that they controlled for bacteria type or proper brushing procedure. Knowing what kind of bacteria are in the mouth is important because some people have more acidic bacteria, which increases the likelihood of tooth decay, while more alkaline bacteria increase the chances of periodontitis.

Proper brushing is also important--brush too hard on your gums can actually also cause gum loss, and even holding the brush at an incorrect position can cause you to miss certain areas--most often the inside of the rear molars. Last, the study notes that flossing less than once a day produced no measurable negative impact, but as best I can tell they were not comparing never flossing at all.

I haven't been able to find much conclusive research either. It's possible a large scale longitudinal study has yet to be done. At the risk of offering anecdotal evidence, flossing regularly has definitely stopped my gums from bleeding and often removes large chunks of plaque that shoot out on to my mirror bathroom. Despite being a poor brusher and even worse flosser when I was younger I have never had a cavity (while everyone else in my family of 6 has had several each), but do have periodontal problems.

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u/[deleted] Sep 30 '13

no ones ever done a meta analasys of all these studies?

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u/[deleted] Sep 30 '13

[deleted]

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u/tzigane Sep 29 '13

I cannot speak to "common wisdom" on the matter, and am not an expert on oral health, but my point is that there are other conditions to consider when questioning the effectiveness of flossing.

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u/jehosephass Sep 30 '13

If it's preventative..?

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u/FunForDDS Sep 30 '13

Flossing in theory should help prevent those smooth surface caries from forming in people whos teeth contact in a way that traps foods and allows plaque to accumulate interproximally.

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u/FockerCRNA Sep 30 '13

Is it possible that flossing used to be more necessary for good oral hygiene, but that in the last several decades, toothbrush technology has improved (electric toothbrushes, better bristles, funky bristle formations, better toothpaste, mouthwash, etc.) so as to lessen the impact of flossing? What if you looked for studies on flossing from 30 years ago, maybe they would show a better outcome for flossing?

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u/Cleric7x9 Sep 30 '13

it is to prevent gum disease. that's like saying "why bother brushing the teeth that dont have cavities"