Wednesday, May 13, 2009

How does toothpaste works?

Since we're kids, we were taught how to brush teeth, and the importance of brushing teeth. Have you wonders, even if we were doing the same thing over and over again, how many of us actually know how toothpaste works? Hmm...

First of all, let me explain what is toothpaste and what is it made from. Toothpaste is basically a gel or paste dentifrice used with toothbrush to maintain oral hygiene and clean our teeth and gum. It can prevent tooth decay and the formation of dental plaque by delivering active ingredients such as fluoride and xylitol.

The most well known ingredient in toothpaste is fluoride. Surfactants (detergents) work well with fluoride to form foam that clean the tooth surface and wash away leftover food between our tooth. Another important ingredient is tetrasodium pyrophosphate (TSSP), which can helps to remove magnesium and calcium from our saliva, so they cannot form tartar or clacified plaque on our teeth. Sodium saccharin is often added as sweetener, to reduce the bitterness of TSSP.

Now, let's have a look at our teeth's structure!

As you can see, the part which we are brushing everyday is the outermost layer, the enamel. 95% of enamel is made from a hard and strong subtance, called hydroxyapatite, Ca10(PO4)6(OH)2. Although hydroxyapatite is strong and firm, it is easily decay if attacked by acid. The reaction occurs is:

Ca10(PO4)6(OH)2 + 8H+ ↔ 10Ca2++ 6(HPO4)2- + 2H2O

This equation means that the reaction will proceed toward the right side by the addition of acid (H+ ion). Thus, the more acid added, the more hydroxyapatite that is dissolved into the saliva. This reaction is called 'decalcification'. Eventually, the enamel will start to decay and thus, plaque is formed.

You don't want your teeth to look like this right? Okay, continue reading then. =D

Now we shall see how toothpaste works to prevent decalcification or tooth decay! For your information, most of the food we consume are composed of different types of food acid. For instance, malic acid (apple), tannic acid (tea) and tartric acid (carrot).

Toothpaste act as a base which neutralise the acids in our mouth. From the above equation, we know that acids attack the teeth and the enamel diffuses into calcium ions and HPO4 2- ions. When we brush our teeth with toothpaste, fluoride ions are delivered to the enamel and replaces the OH ions in hydroxyapatite, to form fluoroapatite, Ca10(PO4)6F2. The reaction occurs is:

Ca10(PO4)6(OH)2 + 8H+ ---> 10 Ca2++ 6HPO42+2H2O

Last but not least, remember to brush your teeth at least twice a day, and also after meal!

Save your smile! =D

Thanks for reading and have a good day!


  1. brush brush brush~~

    i somehow found that some of the ppl dun really brush their teeth, but they will only use listerine to "clean" their mouth and teeth.. @.@

  2. lol.. that means they're very dirty and lazy. haha

  3. no..! ur mouth is dirtier! u noe why?
    coz u only brush ur teeth without listerine-ing!
    only brushing is not enuf~ u dirty mouth~ weeeeeee!

  4. ngek ngek.. im gonna make a topic on listerine to "chai lei gek cheong".. =P

  5. Intresting read on the chemical aspects of what happens when we brush teeth or if we don't brush teeth at all! ;-)

  6. Alice Phua: Thanks for the comment! I will work harder.

  7. kevin ar...nowadays, usage listerine can cause cancer alr...haha...i read from net dun use too much listerine

  8. I have a dumb question! :)) is the 8H in the equation an acid? :D

    1. Yes, since hydrogen ions are produced when an acid dissociates in water.

  9. the reactions are both the same.... it does not clarify the replacement of OH by F

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