The main cause of tooth decay is plaque. Bacteria in plaque feed mainly on simple sugars and starches in food. Bacteria create an acid that gradually destroys the enamel of a tooth, forming a cavity. Enamel is the outer, hard, glossy layer of the chewing surfaces of a tooth. This causes pain and the cavity gets bigger.
Bacteria can next invade the exposed pulp at the center of the tooth and destroy the nerve.
Early dental decay often causes no discomfort. After decay has destroyed much of the hard, outer portion of the tooth, you may get a toothache when you eat hot, cold, or sweet foods. If the cavity is not treated, decay destroys more of the tooth and the pain worsens. In addition to pain, you may notice bad breath and a bad taste in your mouth. In addition, your dentist or hygienist will regularly take x-rays to check for decay between the teeth and under fillings.