What things decay teeth?

All sorts of things, Candy, soda etc.

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Tooth decay is caused by a build up of bacteria on your teeth. This can be easily prevented by regular dental hygiene. You need to brush 3 times a day, floss 2 times a day and use a water pick to regularly remove the bacteria that is gathered on your teeth. Here's a video about how tooth decay actually happens -

http://www.checkdent.com/en/videos/tooth-cavities-89.html