We have got a lot of questions related to dental hygiene from our readers. We asked these questions to be answered by someone who works at an oral microbiology research lab. These are the questions that are answered by him .

  • How does toothpaste affect the microbial flora of the mouth?
  • Why is fluoride recommended to repair enamel?
  • How alcohol based mouth rinses affect the mouth micro biome?
  • Have humans always had to brush their teeth to avoid rotting?
  • How beneficial is it to brush one’s tongue?



Brushing just disrupts biofilms on your teeth basically. Streptococcus mutans and some other strains of strep live in your mouth and eat sucrose in your mouth to make glycan, which is a sticky extra cellular polymer that is water insoluble. This builds up, and sticks to your enamel. Normally this wouldn’t be a big deal, but a lot of the bugs in the oral cavity that cause the most damage are anaerobic, and this polymer provides a safe place to live away from air in your mouth. Your saliva can’t wash them away because the polymer is water insoluble.

While the bacteria are stuck in this polymer, they are creating lactic acid, which drastically lowers the pH of the area right next to your tooth enamel, which can lead to demineralization. Simply brushing the area will break up the polymer and release the bacteria from the area so that you can spit them out before the acid builds up enough to damage your enamel. You’re disrupting all bacteria, good and bad, but the bad bacteria are not necessarily growing faster or better than the good ones, they’re just causing damage the longer they sit on your teeth. The good ones will be able to bounce back just fine (no one brushes well enough to get rid of a significant amount of bacteria anyways) so it’s worth it to disrupt all the bugs and the sticky glycan polymer for the sake of your enamel.

There are lots of other good reasons to brush too (fluoride, gum health, etc) but the biofilm is the reason I’m most familiar with.


To answer your second question, of why fluoride is recommended to repair enamel. A simplified explanation: Enamel is made up of, among other things, the mineral hydroxyapatite. Acids from bacteria leech the OH (aka hydroxy) group from the enamel, which weakens the structure and makes it prone to cavitations. Fluoride replaces the OH (aka hydroxy) group in hydroxyapatite to form fluoroapatite. Fluoroapatite is more resistant acid, which makes the teeth more resistant to decay.

Person Pouring Liquid In Container

Onto the third question, how alcohol based mouth rinses affect the mouth micro biome? Alcohol-based mouth rinses (Listerine) do have antiseptic properties; however, these properties have very little to do with the alcohol itself. The alcohol serves mainly to dissolve the essential oils – menthol, thymol, eucalyptol, etc. These ingredients disrupt bacterial cell walls, inhibit bacterial enzyme activity, block bacterial aggregation on tooth surfaces, and increase bacterial regeneration time. This helps to neutralize the pH of the saliva in the short term and gives anti-plaque and anti-gingivitis properties in the long-term (fantastic benefits for hard to brush areas).

Non-alcohol based rinses are forced to take a different approach. Some use quaternary ammonia compounds that confer anti-plaque properties but have mixed results in granting the long term benefits mentioned above. Others simply use fluoride as an active ingredient, which strengthens enamel and makes its breakdown more difficult but does little to affect bacterial attachment and colonization and is somewhat redundant if brushing normally with fluoridated toothpaste and drinking fluoridated water.

Drama recon - Neanderthals had big faces and big teeth.

Now on to the next question, Have humans always had to brush their teeth to avoid rotting?

The short answer is that no, brushing of the teeth wasn’t necessary. Humans didn’t live nearly as long until recently, and there was no reason to evolve more long-lasting teeth.

The long answer is that there is no selective pressure to produce teeth that last longer. Teeth don’t usually start getting seriously rotten until our third decade of life or so. At this point, we’re already well past sexual maturity and, in prior millenia, would have likely reproduced. Remember, unless a trait gives a reproductive advantage, there’s no selection for it.

A related phenomenon is that humans and their ancestors didn’t live nearly as long in the past. The set of teeth that we have is perfectly sufficient for a lifespan of 25 or 30 years. As we’ve dramatically expanded our lifespan, we’ve had to come up with ways to preserve the teeth we have (by brushing them), or replace them altogether (with dentures).

The main reason humans now get cavities much more frequently now is the change of our diet. Since the industrial revolution, processed foods have become readily available. Bacteria is the primary cause of oral diseases such as cavities (rotting of the teeth). Because of the prevalence of sugars and foods/beverages that makes our mouth more acidic and provides harmful bacteria a source of nutrients, there is a better chance harmful bacteria will thrive.

Brushing Tongue

Finally, How beneficial is it to brush one’s tongue?

There are a couple of main reasons to brush your tongue:

  1. The biggest reason is to get rid of bacteria that lives on your tongue. You won’t get rid of all of it but getting rid of most will prevent your breath from smelling bad. Most of the “bad breath” smell comes from your tongue, not your teeth / gums. Bacteria has a better time sticking to your tongue than your teeth. However, the presence of bacteria on your teeth is worse than bacteria on your tongue.
  2. The mechanical agitation of your tongue prevents pathological problems such as hairy tongue(Google at your own risk).

Also, remember that majority of “Bad breath”, or halitosis, is caused by odor causing bacteria that exists within the mouth. These odor causing bacteria exists within the posterior dorsum of the tongue, or in layman term, near the throat.

Physically scrubbing the bacterial layer of the tongue, or chemically killing the bacteria via mouthwash can effectively remove the odor causing bacteria and reduce halitosis. Simply scraping the front of your tongue will do little to reduce bad breath – you have to scrape the bacteria in the back of your tongue.

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Last Update: April 25, 2016

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