Teeth sometimes have unusual shapes as a result of abnormal development. They may be deformed, pitted, grooved or stained. Some patterns, such as the tubercle of Carabelli are more common among certain ethnic groups.
The abnormality may arise as a result of genetic mutation, viral attack or trauma during the early stages of tooth formation. Abnormal tooth shapes present a problem in tooth cleaning; grooves may be inaccessible to the tooth brush. Unusually large cusps make it difficult for the teeth from opposing jaws to fit nicely together (e.g. during orthodontic treatment), thereby affecting chewing efficiency. Protruding cusps on the sides of the teeth may irritate the tongue or cheeks, causing abrasions, cheek biting, or frequent ulcers. Abnormal tooth morphology is unique to each individual, and may be useful for the forensic odontologist in tracing unidentified bodies.