Tooth decay starts with plaque, a sticky film of bacteria that form on your teeth. When the bacteria come in contact with the teeth, they break down the sugars we eat into acids, which breaks down the enamel, hard, outer layer of teeth. Dental decay is one of the most common problems for both kids and adults. A dental filling is the treatment recommended to restore back function, strength, and tooth structure due to decay (cavity). A filling requires cleaning the tooth by removing the decay and replacing it with a tooth colored filling (composite).