Unsightly stains on teeth are a common occurrence. So common that around 37 million Americans use teeth whitening products regularly. The main ingredient in these products is Hydrogen Peroxide – H2O2 (or carbamide peroxide which generates H2O2 on contact with saliva and teeth). Welcome to our second teeth experiment during which we evaluate the impact of Hydrogen Peroxide on teeth.
The mechanism that hydrogen peroxide removes stains is mostly via oxidation, that is the breakdown of stain causing organic molecules via electron removal. This mechanism is more complex than that of acid oxidation covered in another experiment (link blog post). Under basic (high pH) conditions, one side of H2O2 loses a hydrogen atom, turning H2O2 into highly reactive hydrogen superoxide HO2–, which attacks other molecules. Hydrogen peroxide can also split into two reactive hydroxyl radicals.
Typically, teeth whitening products have between 2-5% hydrogen peroxide. This is usually sufficient to clean minor staining if applied for around 30 minutes. However, I have always wondered what would happen to your teeth if you applied a much high concentration…
Fortunately, I have 35% hydrogen peroxide in my lab, seven times higher than normal whitening products, so I decided to find out.
Materials
- Teeth
- 35% Hydrogen Peroxide
- 250 mL beakers
- Cavity indicator dye
- Deionized water
- Rubber gloves
- Tweezers
Experimental Procedure
I wanted to compare a range of concentrations of hydrogen peroxide, so I created solutions of 5, 15, and 35% peroxide. To start, I poured 150 mL of water into the beaker labeled 5% followed by 25 mL of 35% hydrogen peroxide to achieve the correct dilution. I repeated this with 33 mL of water in the 15% beaker followed by 25 mL of 35% peroxide. No dilution is required for the 35% beaker so I just poured around 50 mL of peroxide.
I used cavity finder dye to get a baseline of the teeth before putting them in the peroxide. It stains areas of exposed dentin (where enamel is gone) red. Some minor damage was visible on the teeth, but that’s what I get for ordering teeth that need to be shipped 4000 miles from Poland. I dropped the teeth in each beaker and let them sit for around four hours. Some gas evolution happened in all beakers throughout the reaction.
After four hours, I took the teeth out from each beaker and examined the visual damage. Nothing visible happened to the 5 or 15% teeth. However, the 35% tooth suffered major damage.
I stained the teeth with cavity finder dye. I found that the 5% did not have any significant changes from the baseline stain. The 15% exhibited a slight increase in cavity formation. The 35% showed a massive increase in exposed dentin, with almost all the enamel gone.
The Science Behind This Teeth Experiment
As discussed in the hydrochloric acid experiment blog post, the primary constituent of teeth is hydroxyapatite (HA). For more details on HA, see the linked blog post here. This mineral is likely oxidized by the hydrogen peroxide in the experiment, leading to decomposition of the enamel. The evolved gas during the reaction is oxygen, which is a product of hydrogen peroxide oxidation reactions.
What To Remember For Teeth Whitening
While this experiment features the use of hydrogen peroxide at concentrations seven times higher than those found in whitening products, it still demonstrates the effects excess whitening may have on your teeth. Specifically, the degradation of enamel, which can lead to cavities and tooth loss. Overuse of whitening products could ironically cause you to lose your smile! However, this is highly unlikely, especially if you follow the directions on the packaging and buy from reputable sources (Crest, Colgate, etc.). If you are still concerned about your enamel health (sorry if we scared you with this experiment!) but want to continue using whitening products, you can supplement your oral health routine with high fluoride toothpaste or fluoride-free hydroxyapatite toothpaste. Keep brushing and stay healthy everyone!
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