Generally when we recommend fillings it’s due to decay (though occasionally it is to fill in a chip or notch in your tooth).
Decay starts as demineralization, where the acid from the bacteria dissolves the minerals out of your teeth. When this gets more severe the tooth structure becomes soft. Once the decay has gone beyond the enamel surface into the dentin we recommend a filling.
A filling is where we remove the decaying tooth structure, leaving the good strong tooth structure. We then replace the area of softened tooth that we had to remove with a filling material that will be strong. This removes the bacteria from the inside of the tooth so that the decay doesn’t progress any further, restores the tooth to function, and helps protect the tooth.