The roots of our teeth are normally covered by a layer tissue, called the periodontal ligament, a specialised tissue that joins the teeth to the surrounding gum & bone. The periodontal ligament is made up of cells, blood vessels, nerves and gum fibres. Sometimes, the periodontal ligament does not cover the root fully as a result of severe trauma. Without a covering layer, the surrounding bone could unite with the tooth root, resulting in ankylosis. When this happens, the tooth that is joined to the bone is prevented from normal eruption. Over a period of time, as other adjacent teeth erupt, the the ankylosed tooth that does not erupt becomes lower than the adjacent teeth. If this goes on for many years, the adjacent teeth may tip over the lower placed ankylosed tooth, thereby trapping it.
See also: Tooth loss