Bacteria in your mouth convert sugar to acidic by-products…they do this as part of their natural behaviour. This acid erodes the enamel which is the tough layer that covers your teeth, eventually leading to a cavity (a hole) that will need to be treated by a dentist. If you leave a cavity long enough the decay can reach the nerve of the tooth and this means you will need to either have root canal therapy or get the tooth pulled out.
Thats why sugary drinks and sweets are bad for your teeth – because they leave sugar in your mouth. But fruit has natural sugar in it so even things that are good for you can contribute to tooth decay. The best idea is not to snack and to brush your teeth after you eat meals!
Hello Erin!! Eating sugary food leaves a nice coat of sugar on our teeth – and bacteria love sugar!! It is such a great food source for them. So, as Kimberley and Amy wrote up here, the bacteria can thrive in out mouths when we eat lots of sugar – and cause damage to our teeth in the process!