Bacteria invade the teeth through a cavity, a crack or a loose dental filling. The pulp of the tooth becomes infected and if neglected, the bacteria will eventually destroy the pulp. The infection can travel through the root canal into the bone of the jaw, destroying it and loosening the teeth. A damaged tooth is sensitive to heat and cold and causes a dull aching or throbbing pain, especially while eating. Filling up the crack or cavity in the early stages is easy. Once the infection reaches and destroys the pulp, root canal treatment is required.