Dirty Mouth? The Science of Teeth Whitening

It seems that as we move further into the 21st century, Americans are using modern techniques to evade everyday responsibilities. Overweight people get liposuction to avoid exercise, singles use the internet to find their “soulmate,” and parents pick up fast food to avoid cooking and cleaning. Another example of this is teeth whitening. I admit, I have on occasion used teeth bleach, simply to whiten my teeth after years of braces, or to give my smile a like “pick-me-up.” However, there are people out there that depend on this process to replace teeth brushing. Sure, it seems harmless and an easy fix to not brushing your teeth twice per day, but what it really happening in your mouth? How are the chemicals in teeth bleach physically changing the color of your teeth? Is it harmful to whiten too often? Let’s explore the scientific processes behind a few different methods of teeth whitening…

First of all, what are teeth even made of? The somewhat translucent, exterior layer of the tooth is called “enamel,” which is made of a crystalline calcium phosphate (a mineral). Since it’s made of so much mineral, it is very strong yet brittle. The criss-crossing layer of minerals creates rod-shaped holes in the enamel, making is porous. The layer underneath the enamel is called “dentin,” which is made up of the same material as enamel in combination with water. It is yellowish in appearance, which causes some teeth to become yellow when they are not clean.


After eating different types of food, another layer called the “pellicle” gradually starts to form on top of the enamel. This layer can be brushed away by a toothbrush or by a dentist who can scrape it off. However, the enamel is porous, so the pellicle (or stain) can get deep into the dentin after years of the pellicle sitting on the tooth. Bleaching agents in whiteners can get down into the dentin to remove these stains. Let’s take a closer look…

“Dentist Supervised” whitening involves the use of a gel that consists of a certain percentage (15-35%) of hydrogen peroxide coupled with the use of a UV light. The hydrogen peroxide, upon entering the tooth, releases “free radicals” to “oxidize” the stain beneath the enamel. Confused yet? It’s really very simple. A free radical is an atom, molecule, or ion with unpaired electrons. When something is oxidized, it loses electrons. Thus we can safely assume that the electrons in the organic compounds in the stain are being donated to those in the free radicals released by the bleach. This causes the degeneration of the stain, and thus the yellow color to disappear. Adding light to the equation accelerates this whitening process.  UV light is known to accelerate many chemical processes, including the oxidation of the stains in your teeth. So while you do have to sit with your mouth open and a light stuck in it for about 30 minutes to 1 hour, you’ll only have to go in once and you won’t have to keep bleach in your mouth for hours at a time.

As you all know, we can obviously also whiten our teeth at home. The difference here is the use of a lower concentrated (10-20%) carbamide peroxide gel (and more time consumption, unfortunately). Carbamide must be broken down into hydrogen peroxide during a separated chemical reaction first during the chemical reaction, which is why it takes longer than if you went to the dentist. Using either custom-made “trays” or over-the-counter “strips.” You can eventually achieve similar results to those from the dentist’s office. You must be careful, however, not to get the gel onto your gums, which are made of soft connective tissue. Leaving hydrogen peroxide on them for too long can causes burns, which will leave your mouth sensitive for a few days.

Hydrogen Peroxide

Carbamide Peroxide

So there you have it, a bleaching gel in combination with UV light causes a simple chemical reaction that removes stain below the enamel layer of teeth. So popular contrary belief, it is science, not magic that changes the color of your teeth. And even though you may be removing the stain, you are not removing permanent damage done to enamel by not brushing your teeth (I’m talking cavities, my friends).


1. “The Chemistry Associated with Peroxide-Based Teeth Whiteners” http://www.dental-picture-show.com/teeth_bleaching/a3_teeth_whitening_science.html

2. “Teeth Whitening – How it Works and What it Costs” http://www.yourdentistryguide.com/teeth-whitening/

3. “Antioxidants and Free Radicals” http://www.rice.edu/~jenky/sports/antiox.html

4. “The Art and Science of Tooth Whitening” http://www.ncbi.nlm.nih.gov/pubmed/15828604

6 thoughts on “Dirty Mouth? The Science of Teeth Whitening

  1. Yes, everyone wants white, shiny teeth, which definitely add scores to your charming smile. That is why although teeth whitening cost hundreds of dollars, those dentists never worry about their business (if you have take microeconomics, you should remember that demand is supposed to decrease with price for a normal goods… but seems the price elasticity of demand is pretty low for teeth whitening).

    I totally agree with the author that, on one hand brushing teeth is to keep your teeth white, but on the other hand, it also keeps them health. In the regard of teeth health, I would like to share a little more of my knowledge. Usually everyone brushes his/her teeth twice a day, once when they get up and once before they go to bed. However, such practice is not quite efficient. Most teeth damages are caused by food residuals on your teeth after you had meals. So the right way is that, each time after you eat, you should brush your teeth – or at least rinse out your mouth with water. It seems troublesome, but to save your money in the future, you may want to do it occasionally.

    It is interesting to see the science behind teeth whitening. It is not surprising, then, that those toothpastes which claim to have teeth whitening effect never work out quite well – it takes a hour at the dentist to whiten your teeth using the gel with much higher concentration of the effective chemical, how long do you spend when you brush your teeth everyday?

  2. I thought that this was really interesting, particularly that the whitening agent is hydrogen peroxide which is a household chemical. I have personally used whitening strips, and I can attest to their effectiveness. But what happened to me was that my teeth became really sensitive to the whitening strips. After I used the strips my teeth would feel like the inside of my teeth (maybe the pulp, looking at the picture you posted) was really cold. I was wondering if you had found anything about whitening strips causing sensitivity and how that happens. From what you posted, I thought that maybe the hydrogen peroxide somehow penetrated to the pulp my teeth and free radicals were oxidizing/reacting with that part of my teeth and that might be causing the pain.

    • yep, I too have used the white strips and experienced sensitivity. In fact I have also tried gel bleach and it can be really painful the next day…almost impossible to drink any liquids. You are right about the pulp (which contains nerve endings). There are tiny tubules that extend from the exterior of the tooth down to the pulp, and these are usually plugged up by small minerals in the saliva. Sometimes when you bleach the teeth or leave it on for too long, the hydrogen peroxide will dissolve these minerals, allowing liquid to move into the tubules. This is the cause of the discomfort and sensitivity.

  3. I thought this was a really interesting article, but was interested to see what the requirements for children whitening their teeth were. With shows like Toddlers and Tiaras out, it seems like treatments like this will begin happening younger and younger and it made me wonder if there would be any long term affects if you start whitening too early. It turns out that the pulp chamber is enlarged until about age 16 so it is not a good idea to start before then as there is the increased risk for sensitivity.


  4. While it is understandable that people want to have pretty white teeth, since people all love beauty, but in using tooth whitening, there are a lot costs you should consider. Not to mention the high cost of tooth whitening products, the side effects of using them make me doubt that whether it is worth it. Teeth usually become sensitive to temperatures after using the product, as will feel it when you have hot or cold drinks. Teeth enamel, which helps us prevent tooth decay, may be removed if one use bleach or tooth whitening chemicals frequently and thus causing increased chances of tooth decay. Like Ann and Courtney mentioned, sore gums, irritation of gums and allergic reactions might occur immediately after tooth whitening procedure.
    Knowing the danger of teeth whitening products, if you still want to go ahead and do it, I would suggest using whitening toothpastes first. Although whitening toothpastes only help remove surface stains and do not contain bleach, and it can only lighten your tooth’s color by about one shade compared to three to eight shades with the use of other products such as bleach, the fact that it only contains gentle polishing or chemical agents would not hurt your teeth that much as well. Thus if you just want to whiten you teeth a little bit, you don’t have to go to the extreme. To the end, it does not worth it to hurt your health for beauty.


  5. Like cbrimm, I can also attest to the efficacy of whitestrips. After getting my Invisalign removed, I had litle white squares in the middle of my teeth, so the dentist gave me some Crest WhiteStrips. As Annie mentioned, this alternative version of teeth whitening requires a more lengthy process. According to Crest, you must apply the strip twice daily for 30 minutes each and for about two weeks. However, I was wondering how the free radicals actually have time to enter into pores and oxidize the stains. I mean, even with UV light, which accelerates the reaction, the process lasts roughly an hour. I know the UV light process does a more thorough whitening process within that given hour, but I guess I am wondering how long the reaction occurs without the presence of UV light, in a lower concentration of hydrogen peroxide (which first must be broken down, accounting for even more time)?

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