A nerve that has died eventually causes severe irritation and pain from the bone just outside the root tip. If bacteria (circulating in the blood flow) settle in the area of damaged bone and gum, the bacteria multiply; spreading the infection and causing further bone damage and more pain. So, while the “dead” nerve inside the tooth is no longer causing pain, the nerves in the jawbone and in the living tissue outside the root tip cause pain. Usually this pain is from chewing pressure or from touch or tapping, and can become excruciating. The pain from the bone is called “an abscess” if bacteria are present, but can be just as painful when not infected.