Eruptive movements of ectopic permanent mandibular canines: a case series study based on serial orthopantomograms...

The purpose of this study is to evaluate the patterns of eruptive movements of ectopic mandibular canines observed on series of orthopantomograms from each individual. The hypothesis is that the eruption direction might be predicted from the location and morphology of the permanent canine.

Radiographic material was forwarded from orthodontic colleagues in Denmark and the Nordic countries. In 16 cases/individuals with unilateral or bilateral mandibular canine ectopia, more than one orthopantomogram from each individual was forwarded. The material consists of 41 radiographs from these 16 individuals. In each, the primary mandibular canine existed in the first taken orthopantomogram. The radiographs were taken with the same radiographic equipment, but not necessarily with the same settings and patient orientation. The material was divided according to unilateral ectopia (10 individuals) and bilateral ectopia (6 individuals), and according to the initial location of the permanent canine, compared to the axis of the primary canine (Ax) in the posterior location and anterior location. The following were registered: ages, lengths of age interval between orthopantomograms, canine maturity, root morphology, crown morphology, and location of permanent canines expressed in distances and angles.

The following were concluded. Ectopia was diagnosed earlier in bilateral cases (about 9 years of age) than in unilateral cases (about 12 years of age). More radiographs were taken for each child in the bilateral group, compared to the unilateral group. Extraction of the primary canines occurred often in the bilateral group, but seldom in the unilateral group. The posteriorly located unilateral ectopic canine was located further posterior, compared to the Ax, than bilateral cases. The crown morphology changed during the eruption movements. Curved root morphology appeared in the bilateral cases. Three different patterns were registered in canine eruption (upward, downward, and anterior movements), seemingly dependent on the location and crown morphology of the permanent canine. In bilateral cases, the eruption deviation was most severe on the left side.

There are considerable differences between unilateral and bilateral ectopic permanent mandibular canines. The differences are predominantly in the age of the children when ectopia is diagnosed, the number of orthopantomograms taken, and furthermore the location, crown morphology and eruptive movements of the ectopic permanent mandibular canine.