Everyone has heard about soda, coffee, and tea being bad for your teeth. But what in these drinks actually causes tooth decay? It is all about chemistry and the fact that acid and teeth don’t go well together. pH is a metric for determining the amount of hydrogen ions (H+) or more accurately hydronium ions (H3O+) are in a substance:
pH = -log10[H+]
Acids have a low pH, meaning a high amount of H+ is present. Hydrogen ions are highly reactive and can attack other substances by “stealing” their electrons, otherwise known as oxidation. For teeth, acids can oxidize the outer layer of enamel, promoting the formation of cavities and potential tooth loss. Soda especially has a considerably low pH, typically around 2.5-3.5. For comparison, water has a pH of around 7 and coffee at about 4.85. Since pH is logarithmic, this means that soda is around 140 times more acidic than coffee and 32,000 more acidic than water! You can only imagine the damage soda does to your teeth over the years.
In this blog post, I wanted to investigate an extreme example of acid’s effect on teeth. I put teeth in 31.45% hydrochloric acid, which has a pH less than 1.0, making it at least 31.6 times more acidic than the most acidic sodas. Then I examined the effect on the enamel using a special cavity finder dye.
Materials
- Teeth
- 31.45% Hydrochloric Acid (also known as muriatic acid)
- 250 mL beakers
- Cavity indicator dye
- Deionized water
- Rubber gloves
- Tweezers
Experimental Procedure
I poured out approximately 100 mL of hydrochloric acid into one of the 250 mL beakers (if you’re tempted to smell the acid… don’t. It does not smell good. Trust me.). Then I took a tooth and dropped it into the acid beaker. The tooth immediately reacted with the acid, producing gas bubbles. I left the tooth in the acid for about an hour, over which the tooth was massively disintegrated by the acid. It broke in several smaller pieces and had a weird translucent film coming off of it.
Although the tooth was undoubtedly destroyed, I wanted to see how bad the damage was by using a cavity finder dye. This dye stains the inner dentin of teeth, which is never exposed in healthy teeth unless the enamel is gone. I needed a good baseline of how the dye stains healthy teeth, so I put a few drops of dye onto a normal tooth. Then, I washed the excess dye off in water. Hardly any dye stuck on the healthy tooth, which means the enamel is generally intact. I repeated the same procedure for the acid tooth. The difference between the two is night and day. The entire surface of the acid tooth was a deep pink color, indicating that the enamel was destroyed.
I was curious what the acid would do to the tooth if I left it in for 24 hours, so I put the remains of the acid tooth back into the acid beaker. After a few hours, the tooth has completely dissolved, leaving a yellow solution likely from dissolved chlorine from the acid and other impurities.
Understanding the Science
The primary constituent of teeth is hydroxyapatite (HA). HA is a mineral composed of calcium and phosphate structures bound together by oxygen.
Figure reference: https://doi.org/10.1016/j.ceramint.2021.07.100
When reacted with hydrochloric acid, the HA in teeth was attacked by H+ ions and likely degraded into monocalcium phosphate and calcium chloride, which are both highly soluble in water. These water-soluble molecules are wicked away from water (and salvia for teeth in mouths), leaving fissures in the enamel. The observed gas evolved during the reaction is likely oxygen and carbon dioxide from the degradation of organic molecules in the teeth.
What To Remember For Healthy Teeth
Even though this is a very extreme version of the effect acid can have on your teeth, the same principles still apply to your oral health when consuming acidic beverages. Your enamel will degrade over time if you overconsume acidic drinks. This certainly does not mean that you have to stop drinking your favorite beverages though! I certainly still drink coffee every now and then (I don’t know how I would get through tough days at work without coffee). The important concept to remember is both moderation and to have a solid dental hygiene routine. You can prevent acidification of your mouth by brushing your teeth properly and by limiting your intake of super acidic drinks like soda. To strengthen your enamel and prevent degradation, you can use toothpaste with sodium fluoride, stannous fluoride, or fluoride-free hydroxyapatite toothpaste. Keep brushing and stay healthy everyone!
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