Toothache is a result of pain in the area of the face and jaw, usually caused when a nerve in the root of the tooth becomes irritated. However, other problems such as infection, decay, or the loss of a tooth, can also cause toothache. Toothache occurs when the pulp inside your tooth gets inflamed. This is often caused by dental decay. Dental decay is when bacteria in your mouth break down the enamel of a tooth. Holes (cavities) in the tooth often develop, exposing the nerves underneath.