External resorption is a process that affects the roots of a tooth and typically starts at the outermost of the tooth where the root connects with the jaw bone through the ligament holding it in the socket, explains Dr. Barry F. McArdle, D.M.D. Resorption is independent of decay and fracture.
External resorption is difficult to treat, and in some cases, a tooth loss is inevitable, explains Dr. McArdle. It is an aggressive process that invades the blood vessels and connective tissues in a tooth's root from the root's surrounding structures below the gum line. Color changes on the tooth can be a sign of external resorption, but an X-ray gives an accurate diagnosis.