How does toothpaste prevent tooth decay?
(Lansing State Journal, August 9, 1995)
When bacteria digest food in our mouths, they release weak acids, especially when we eat sugars. Acids are chemicals that release positively charged hydrogen ions when dissolved in solutions such as saliva. Our teeth have a hard covering called enamel that is weakly basic. Bases are chemicals that release negatively charged ions called hydroxyl ions when dissolved in solution. When bacteria make our mouth acidic, the acid reacts with our enamel, removing hydroxyl ions, causing tooth decay.
The active ingredient in toothpaste is a fluoride salt. When toothpaste dissolves in our mouths, negatively charged fluoride ions are released. The fluoride ions are similar to other hydroxyl ions in that they are negatively charged and can take the place of hydroxyl ions that have reacted with acid. Also, fluoride ions don't react with acid as easily as the hydroxyl ions, making enamel more resistant to decay.
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