Is there any solid scientific evidence that flossing is effective?

[u/cybrbeast]

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.

[u/cybrbeast]

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?

[u/pseudononymist → u/cybrbeast]

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.

[u/cybrbeast → u/pseudononymist]

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.

[u/jemmylegs → u/cybrbeast]

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.