Double teeth are the result of disturbances during embryological tooth formation. Since it is not possible to know what caused the embryonic disturbance, it is not appropriate to use terms such as gemination and fusion when talking about a diagnosis. One of the embryological causes of double teeth is gemination. Gemination is an attempted division of a tooth germ, resulting in a tooth with a bifid crown and a single root. The error occurs at the proliferative stage of tooth development.
Fusion occurs when two or more tooth germs form a single tooth.
In cases of complete fusion, the tooth germs unite before the calcification process begins, and it results in a fused tooth with only one root canal. In a variant of fusion, known as concrescence, the fusion occurs at the embryonic stage when the cementum layer of the root is forming. Fused or geminated teeth usually have a vertical groove on the front and back of the teeth. These grooves may be very difficult to clean, leading to dental stains and caries. This problem can be corrected by placing a sealant or composite material into the grooves to decrease the risk of caries.