While decay often is cited as the primary cause of a toothache, it's important for you to have a complete oral examination to determine the cause. Other dental causes of a toothache include: dental abscess (infection in the nerve of a tooth), gum disease, grinding teeth (bruxism), previous tooth trauma and an abnormal bite. Tooth eruption may be the cause of tooth or jaw pain in babies and school age children.
TMJ, sinus or ear infections, and tension in the facial muscles can cause discomfort that resembles a toothache, but often these health problems are accompanied by a headache. Pain around the teeth and the jaws can be symptoms of heart disease such as angina. If your dentist suspects a medical illness could ba the cause of your toothache, he or she may refer you to a physician.
Source: Academy of General Dentistry