Surprisingly Little Evidence for the Usual Wisdom About Teeth
Aaron E. Carroll
I brush my teeth twice a day, but not for as long as my dentist would like. I’d like to say I floss regularly, but that would be stretching the truth. I don’t scrape my tongue, I don’t rinse with mouthwash and I don’t use an interdental brush or Waterpik. However, I have one filling in my mouth, and I got that only when I had braces as an adult 15 years ago.
My wife, on the other hand, cares for her teeth fastidiously. She does all the things you’re supposed to do, and then some. But she has more fillings than I can count. I remember once, years ago, when one of her teeth broke while she was eating scrambled eggs.
Clearly, the stuff we’re doing might not make as much of a difference as we think. A couple of weeks ago, many of you were shocked to learn that the evidence supporting flossing daily was as thin as, well, dental floss. That’s just the beginning.
As my colleague Austin Frakt pointed out recently, for adults without apparent dental problems, there’s little evidence to support the use of yearly dental X-rays. This still doesn’t prevent many dentists from recommending them for everyone.
With respect to flossing, this shouldn’t have been news either. A systematic review in 2011 concluded that, in adults, toothbrushing with flossing versus toothbrushing alone most likely reduced gingivitis, or inflammation of the gums. But there was really weak evidence that it reduced plaque in the short term. There was no evidence that it reduced cavities. That’s pretty much what we learned recently.
My dentist has always recommended a powered toothbrush. The evidence seems to agree that, as many randomized controlled trials confirm, powered toothbrushes reduce both plaque and gingivitis more than regular toothbrushes. An older Cochrane review concluded that the rotating powered toothbrushes were superior than the side to side powered brushes. I use the latter, and this disappointed me. But the difference between the two types, while statistically significant, was really small.
There appear to be no good randomized controlled trials on brushing frequency. The other studies that do exist, while flawed, seem to support twice-a-day brushing.
Surely the twice-a-year teeth cleanings matter? In 2005, Evidence-Based Dentistry highlighted a systematic review on the effects of routine scaling and polishing (you call it teeth cleaning).
Researchers found eight randomized controlled trials that were on point, but they were all judged as having a high risk of bias. The results were all over the map. Their conclusions were that the evidence isn’t of sufficient quality to reach any conclusions as to the benefits or harms of scaling and polishing.
Regardless, I’ve been told by all the dentists I know to have it done every six months.
When filling cavities, some dentists advocate bonded amalgams over non-bonded amalgams. There’s pretty much no evidence to support that practice, though. The one randomized controlled trial didn’t seem to support their use, especially since they cost much more. Previous, nonrandomized controlled trials in children didn’t really show a difference either.
Has anyone ever told you to use an interdental brush to get at the plaque between your teeth? In 2015, Evidence-Based Dentistry summarized a Cochrane Review of seven randomized controlled trials looking at how interdental brushing in addition to tooth brushing compared with toothbrushing alone or toothbrushing with flossing. Almost no long-term benefits have been proven.
What about preventive dental visits themselves? In 2013, Bisakha Sen, Nir Menachemi and colleagues used data from the Alabama Children’s Health Insurance Program to follow more than 36,000 children to see how preventive dental visits affected dental care and spending over time. They found that preventive visits were associated with fewer visits for restorative dental care in the future, implying that there was an improvement in oral health. But they found that, for the most part, more than one annual preventive visit in children was not cost-effective.
Further work found that it may have been the use of sealants, and not preventive visits in general, that had this protective effect. Since sealants could be applied without an actual visit to the dentist, that brings into question whether a more cost-effective means of getting sealant on children’s teeth might be possible — using a lower-cost dental hygienist, perhaps. Fluoride varnish appears to work well, too.
No review of dental health would be complete without at least acknowledging water fluoridation. Much of the evidence is old because it’s getting hard to do studies. It would be somewhat unethical to withhold fluoridation at this point from some people, because the evidence in favor of the practice is so compelling.
In fact, fluoride is so important that the U.S. Preventive Services Task Force recommends that in areas where the water supply is deficient, providers prescribe oral fluoride supplementation to children. They recommend the use of fluoride varnish as well.
To recap, there’s good evidence that brushing twice a day with fluoride toothpaste is a good idea, especially with a powered toothbrush. For children, there’s good evidence that the use of fluoride varnish or sealants can be a powerful tool to prevent cavities. The rest? It’s debatable.
I should note that the lack of evidence doesn’t mean that many of these things don’t work. It just means that we don’t have good studies to back their use. In that case, we must weigh the potential harms against the unproven benefits. With flossing, which is cheap and easy, it still might be worth doing. With scaling and polishing, as well as preventive visits, which are expensive and can hurt, it’s more questionable.
We should also recognize that there are a lot of things outside of our control. Some are genetic. The strength of our enamel most likely determines how easily bacteria can break through defenses. Salivary flow and composition help determine how easily we can clear dangerous bugs. Tooth morphology can leave some teeth more susceptible to infection.
Other things have little to do with dentistry. What you eat can affect your dental health. More important may be mother-to-child transmission of bacteria. Children aren’t born with mouthfuls of germs. Studies show that cavity-causing bacteria get passed directly by parents (mostly mothers) to children, probably by sharing silverware or by other mouth-to-mouth transmission. There’s a reason that mothers with lots of cavities sometimes have children who suffer the same.
There are things we can do to prevent cavities and preserve our oral health. We should focus on those things. We should study the things we debate. But we should also be willing to admit that some of the things we do make no difference at all, and perhaps, should be reconsidered.