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.

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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).

References:

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