Internal resorption is an unusual condition of a tooth when the dentin and pulpal walls begin to resorb centrally within the root canal. The first evidence of the lesion may be the appearance of a pink-hued area on the crown of the tooth; this condition is referred to as pink tooth of Mummery, after the 19th century anatomist James Howard Mummery, and represents the hyperplastic, vascular pulp tissue filling-in the resorbed areas. The cause can sometimes be attributed to trauma to the tooth, but other times there is no known etiology. If the condition is discovered prior to perforation of the crown or root has occurred, endodontic therapy (root canal therapy) may be carried out with the expectation of a fairly high success rate.
External resorption is an inflammatory process in which a tooth root is dissolved away from the root surface inward, toward the pulp. As the tooth resorbs, the space it previously occupied is replaced with bone or granulation tissue. There are a variety of factors that can pre-dispose a tooth to external resorption, including chronic inflammation, rapid orthodontic tooth movement, use of heavy orthodontic wires, trauma to the tooth in which it was displaced (luxated) or avulsed (knocked out completely) and re-planted. Treatment of external resorption can include root canal therapy, surgery, observation, or extraction.
Root resorption is the breakdown or destruction, and subsequent loss, of the root structure of a tooth. This is caused by living body cells attacking part of the tooth. When the damage extends to the whole tooth, it is called tooth resorption. Deciduous root resorption is a natural process which allows exfoliation of the primary teeth to make way for the secondary teeth. Deciduous root resorption is caused by osteoclast differentiation due to pressure exerted by the erupting permanent tooth. Root resorption of secondary teeth can occur as a result of pressure on the root surface. This can be from trauma, ectopic teeth erupting in the path of the root, inflammation, excessive occlusal loading, aggressive tumors and growths. The most common cause in Western Society is orthodontic forces. Severe root resorption is very difficult to treat and often requires the extraction of teeth.