MANDIBULAR LATERAL INCISOR-CANINE TRANSPOSITION, CONCOMITANT DENTAL ANOMALIES, AND GENETIC-CONTROL

Mandibular lateral incisor-canine (Mn.12.C) transposition is a rare de velopmental disturbance of tooth order characterized by positional int erchange of the two teeth. In children with Mn.12.C anomaly, the mandi bular lateral incisor shows distal ectopic eruption and the adjacent c anine subsequently erupts mesial to it. A sample of 60 orthodontic pat ients with Mn.12.C transposition was studied using roentgenograms take n at the time of diagnosis. Two age-related phenotypes of the anomaly were identified: early-stage (median age, 9 years) and mature-stage (m edian age, 12 years). Mn.12.C transposition occurred bilaterally in 10 subjects (17%) and favored female expression (sex ratio, M1 :F3) and right-side occurrence (68% of unilateral cases). Statistically signifi cant associations were found between Mn.12.C transposition and increas ed frequency of tooth agenesis (M3, p<0.01; MnP2, p<0.01 ) and peg-sha ped maxillary lateral incisors (p<0.0001). The results from this study and the analysis of 50 previously published cases provide evidence th at Mn.12.C transposition is a disturbance of tooth order and eruptive position probably caused by genetic influences. The Mn.12.C anomaly li kely results from genetic mechanisms similar to those responsible for occurrences of its associated dental anomalies, such as tooth agenesis and peg-shaped maxillary lateral incisors. In an appendix, clinical o rthodontic management of Mn.12.C transposition is discussed, based on treatment data derived from the study sample.