A radiograph shows the maxillary canine and first premolar occupying each other's positions in the arch. What is this anomaly called?

Correct answer: C. Transposition

• A. Impaction is failure to erupt because of a physical obstruction or lack of eruptive force. Both teeth here have erupted.
• B. Ectopic eruption is eruption in an abnormal position or direction — the maxillary first molar erupting into the distal of the second primary molar is the classic example — but it does not involve two teeth swapping places.
• C. CORRECT. Transposition is the positional interchange of two ADJACENT teeth within the same quadrant, in which each has erupted into the other's place in the arch. The maxillary canine and first premolar is by far the most common transposition.
• D. Migration is drift of a tooth from its position, usually into an adjacent edentulous space, without a positional exchange.

Note: The two common transpositions: maxillary canine with first premolar (most frequent), and maxillary canine with lateral incisor. Management is usually to accept the transposed position and reshape, since orthodontically moving the roots past one another risks resorption and is often not feasible.