By Jop de Vrieze

Do we brush our teeth too often?

The composition of the oral microbiota is partially determined by what we eat and by our oral hygiene habits. Researcher Jop de Vrieze tried to find out if not brushing one’s teeth could be better for our oral bacteria.

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Jop de Vrieze is freelance science writer and author of the book ‘Allemaal Beestjes’ [‘Critters and Crawlers’].

Just like other body surfaces, the mouth has its own microbiota, which is dominated by bacteria. Similar to the gut, its composition differs from person to person and will comprise both beneficial and harmful bacteria. 


Many people would cringe at the idea of not brushing their teeth for even one day. Still, 41 participants in a study by the Academic Centre for Dentistry in Amsterdam were found willing to leave their toothbrush alone for no less than two weeks. They were asked to do this because the researchers wanted to find out about the differences in the response of healthy volunteers to their “experimental gingivitis challenge”, i.e. experimental inducement of gum inflammation.


During the two weeks of no brushing, the researchers made photos of the participants’ teeth with a special camera that will make a certain protein, produced by inflammation-inducing bacteria present in dental plaque, light up red. Their observations exceeded their expectations. A number of participants quickly developed nasty inflammations, even bleeding gums in some cases, they wrote in Journal of Dentistry. Another group had mild symptoms. But the most compelling finding was that a third of participants did not develop any symptoms. They did have dental plaque, but it did not light up red and did not trigger inflammation. ‘Yes, that did surprise us very much’, says preventive dentistry professor Wim Crielaard, principal investigator of the study.  

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 “By our continual brushing, we may be removing beneficial bacteria as well”



To this day, oral hygiene is understood to mean that the mouth needs to be kept as clean as possible by brushing, flossing, picking and rinsing to prevent harmful bacteria from causing cavities or inflammations. However, following the example of researchers specialized in gut bacteria populations, scientists are now beginning to see the mouth as an ecosystem of various bacteria. Some of those are harmful, but most of them are not and some are even beneficial. And by our continual brushing, we may be removing the latter category as well, giving their harmful counterparts an opportunity, time and again, to take over. In a truly healthy mouth, however, beneficial bacteria and your saliva will keep harmful bacteria in check.


Teeth cleaning is something people have been doing in various ways for centuries. However, the consistent twice-daily brush-and-toothpaste routine did not develop until the 20th century. In the more distant past, teeth cleaning was less of a necessity, because people did not consume sugar in the quantities or with the frequency that are common today. Harmful bacteria such as Streptococcus mutans convert sugars into acids that degrade tooth enamel and cause cavities, and create an environment in which harmful bacteria can thrive.


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In recent years, reports have surfaced criticizing the effect of brushing on beneficial bacteria that live in the mouth. The criticism is levelled mainly at triclosan, an antibacterial ingredient in some toothpastes. American researchers who had concerns about the impact of this substance on oral and intestinal flora decided to subject it to a test. Contrary to their expectations, they found no significant difference in the composition of the bacterial populations of those using triclosan-containing toothpaste and those using another toothpaste, as reported in the May issue of mSphere. ‘This could be because we conducted the measurement just prior to brushing instead of just after’, says Julia Parsonnet, principal investigator at Stanford University. ‘However, it could be that toothpaste without triclosan unbalances the oral microbiome by about the same degree.’


Toothpaste almost always contains an abrasive, fluoride and, in many cases, a foaming agent. Fluoride has been shown to have a mild antibacterial effect, and there is hardly any research into the effects of other toothpaste ingredients on oral bacteria. Foaming agents, for instance, are known to dissolve the oral mucosa, which modifies the circumstances in the mouth, although it is not clear if that causes shifts in the bacterial population. The actual brushing action itself could possibly be the most disruptive factor: the mechanical removal of dental plaque. It could be that by brushing their teeth, people’s oral health becomes dependent on it, whereas allowing one’s oral flora to develop a natural balance may make brushing superfluous.  


However, according to Crielaard, how to maintain the ideal balance still remains “the billion dollar question”. Predisposition plays a role, but the single most important factor is diet. If someone consumes a lot of sugar and not enough fibre-rich foods, such as raw vegetables that remove impurities, they will have no other option but to use a toothbrush. In 2009, other researchers already presented evidence that people following a “Palaeolithic” diet do not develop gingivitis, despite not brushing their teeth. But as long as there is no conclusive evidence that brushing healthy teeth is actually harmful, people are still advised to brush twice a day.  



This article was previously published in Volkskrant supplement Sir Edmund on 24 September 2016. 

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