A panoramic radiograph shows a mandibular canine that has crossed the midline and now lies within the alveolar bone of the contralateral side. What is this phenomenon called?

Correct answer: D. Transmigration

• A. DILACERATION is an abrupt angular bend in the root or crown of a tooth, usually the result of trauma to the developing tooth germ. It describes tooth FORM, not tooth position.
• B. TRANSPOSITION is the interchange of position of two ADJACENT teeth within the same quadrant — the maxillary canine and first premolar being the commonest pair. There is no midline crossing.
• C. ECTOPIC ERUPTION is eruption in an abnormal position within its own region, classically the maxillary first permanent molar resorbing the distal of the second primary molar. It does not involve crossing the midline.
• D. CORRECT. TRANSMIGRATION is the pre-eruptive migration of an unerupted tooth ACROSS the mandibular midline. It is essentially confined to the mandibular CANINE, is usually unilateral, and is often discovered incidentally. The affected tooth is typically horizontally positioned and may travel a considerable distance beneath the apices of the incisors. Management depends on the extent of migration: early detection may permit surgical exposure and orthodontic traction, whereas a tooth that has travelled far past the midline is usually extracted or, if asymptomatic and deeply placed, monitored.

Note: ⚑ The contributor warned this image is deceptive: at a glance the transmigrated canine lying beneath the incisor apices can be mistaken for a FUSION or gemination of the incisors. Trace the outline of each crown and root separately before interpreting.