Posterior initial siteUnilateral group

The results are illustrated in Table 1 and Fig. 3.

Table 1 Unilateral ectopia of mandibular permanent canines/initial site, posteriorFig. 3

Overview of five unilateral ectopic permanent mandibular canines initially posteriorly located compared to the axis of the primary canine. The cases in the figure are 1, 4, 2, 6, and 8 listed in Table 1. The five cases are arranged according to the initial maturity scores of the mandibular canines from score 3 (Case 1) to score 5 (Case 8). In all cases, two orthopantomograms were available, marked as first radiograph and last radiograph. The orthopantomograms were flipped horizontally to appear on the right side in the five cases because the unilateral ectopic canines occurred on the left side in these cases. The differences in crown morphologies are highlighted in the following: Case 1: Initial crown morphology: Rotated. The eruptive movement of the canine during 12 months was slightly in an anterior and downward direction. In the second radiograph, the crown had attained a lateral morphology. Case 4: The initial crown morphology: Lateral. The eruptive movement of the canine during 36 months seems to be in the anterior and downward direction. In the second radiograph, the crown still has a lateral morphology. Case 2: Initial crown morphology: Facial. The eruptive movement of the canine during 12 months is slightly anterior and in anupward direction. In the second radiograph, the crown on the canine still has a facial appearance. Case 6: Initial crown morphology: Rotated. The eruptive movements of the canine during 12 months are slightly anterior and slightly upward. In the second radiograph, the crown on the canine still has a rotated appearance. Case 8: Initial crown morphology: Lateral. The eruptive movements of the canine during 11 months are in a slightly anterior and downward direction

Ages: In the nine patient cases registered, the ectopia was first diagnosed on orthopantomograms at the ages between 11 years, 2 months and 13 years, 7 months. In two cases, the ages were not available.

Numbers of orthopantomograms: In all cases, the numbers of existing orthopantomograms were two, and the time interval between the two orthopantomograms was from 8 to 36 months.

Canine maturity: The maturity of the canines, when first registered, was from the initial stage of tooth formation (1 case) until complete root formation (3 cases).

Morphology: The morphology of the roots was in all cases straight and the crown morphologies appeared initially either with facial, lateral, or rotated appearances.

Location: The locations and movements of the five cases are demonstrated in Fig. 3. These are cases no. 1, 4, 2, 6, and 8 (Table 1).

Concerning the locations of the permanent canine, the distance observed between the permanent apex and the Ax indicated that the canines initially were severely distally located in a close relation to the root of the first premolar. In all cases, this distance diminished from the first to the second radiographs. These changes in distances indicate anterior movement of the ectopic permanent canine. In one case where the crown had a lateral appearance (case 4 Table 1), the canine moved 17.5 mm anteriorly for 36 months.

The angulation between the primary canine and the permanent canine also changed during the observation period. In most cases, this angle enlarged, resulting in a direction of the permanent canine pointing more downward. This is what appeared in case 4 (Tabel 1, Fig. 3), where the angle between the axis of the permanent and primary canines increased from 80.2 degrees to 99.8 degrees. The initial crown morphology in case 4 was lateral L. In case 6 (Table 1, Fig. 3), the permanent canine moved less than 1 mm anteriorly for 12 months and the canine moved slightly upward. In this case, the canine had the initial maturity score 4, and the crown morphology was rotated, R. In case 2 (Table 1, Fig. 3), the crown had facial appearance F, and the movement of the canine for 12 months was slightly upward.

In the five cases demonstrated in Fig. 3, the initial crown morphologies were facial (1 case) rotated (2 cases), and lateral (2 cases). In the cases demonstrated, the initial maturity of the canines was three in two cases, four in two cases, and five in one case.

Figure 3 focuses on the importance of the morphology of the permanent canine crown for predicting the eruptive pattern. Canines with initial lateral appearances seem to move downward, but an extended study with more material is needed for confirmation. Table 1 indicates that upward movement of the canine toward the occlusal plane (lowering of the angle between the primary and permanent canine) does not occur when the canine on OPs appears in a rotated or lateral position. The importance of the canine maturity for prediction of the eruptive movements cannot be concluded.

General dentition: Dental deviations are observed in the dentition. These are taurodontia and agenesis in five of the nine cases (including one case with agenesis of the third molars).

Bilateral group

The results are illustrated in Table 2 and Fig. 4.

Table 2 Bilateral ectopia of mandibular permanent canines/Initial site, posteriorFig. 4

Overview of the bilateral ectopic mandibular canine regions from the six cases presented in Table 2 (Case 10–15). In cases where the ectopic canine occurred on the left side, the orthopantomogram was flipped horizontally so that all cases studied appeared on the right side. The left ectopic cases in the individual are presented to the left in the figure (first, second, last) and the right ectopic cases in the individual (first, second, last) are presented turned horizontally and appear to the right.Three radiographs appear in four cases, four radiographs in one case, and five radiographs in one case. Comparison of the left and right side Crown morphology initial: The initial crown morphology in the right side of the Figure has facial appearances in all six cases. In the left side of the Figure, facial and rotated initial morphology appears. Canine maturity initial: Canine maturity seems to be close to identical in the two sides. Root morphology: Curved morphology seems to be more frequent on the left side of the Figure compared to the right side, but with small deviations. Eruptive movements: In the left side, the canines are seemingly not moving upward, as the angulation degrees increase. In the right side, all canines seem to move upward. As a conclusion, there is a difference between the left and right regions of ectopic bilateral canines. Canines in the right region of the individuals seem to move occlusally compared to canines in the left regions. General dentition: Deviations in the dentition are observed in five of the six cases with bilateral canine ectopia, but no deviations are observed in case 15

Ages: In the six patient cases registered, the ectopia was first diagnosed on orthopantomograms at the ages between 8 years, 0 months and 10years, 0 month.

In all six cases, the ages were available.

Number of orthopantomograms: The numbers of orthopantomograms in each case were from three to five radiographs (Table 2), and the time intervals between the orthopantomograms taken were from 5 to 48 months.

General dentition: General dental deviations are observed in the dentition, such as taurodontia, agenesis in four of the six cases, and in one case diminutive lateral maxillary incisors appeared. In only one case other dental deviations (except canine ectopia) did not occur.

Subdivision of the bilateral groups. As all the six cases appeared with bilateral mandibular canine ectopia, 12 regions of ectopic canines were registered. Accordingly, distinctions between the left and right appearances in patients could be established. The findings are presented on the left side and right side are shown in Fig. 4.

Bilateral ectopia, individual’s left side

Maturity: The canines, when first registered, were immature, from the initial stages of root formation 0–2.

Morphology: The morphology of the roots was in most cases straight, but also curved morphologies occurred. In two cases, the initial morphology was curved. The initial crown morphologies had facial, lateral, or rotated appearances.

Locations: Concerning locations of the ectopic permanent mandibular canine, the distance between the permanent apex and the Ax axis indicated that the canine was distally located, but not in close relation to the root of the first premolar. In cases where information was available, this distance diminished from the first to the second radiograph. These changes in distances indicate anterior movement of the ectopic mandibular canine. In one case where the crown had a facial appearance (case 10, Table 2), the canine moved anteriorly and the angulation increased, indicating that the canine moved downward. The crown morphology changed during 48 months from F to R.

The angulation changed during the observation period in most cases to a direction pointing more downward. In case 14, the opposite was observed. For 22 months, the angle seemed to diminish. This improved the possibility of orthodontic treatment.

Bilateral ectopia, the individual’s right side

Maturity: The permanent canines, when first registered, were immature from the initial stages 0–2.

Morphology: The morphology of the roots was in three cases straight and in one case straight in the beginning and later curved. In one case, the initial morphology was curved. The permanent crown morphologies appeared with facial appearance in all five cases and only in two cases the morphology changed from facial to rotated and ended up with lateral or rotated appearances.

Locations: Concerning locations of the permanent canine the distance between the permanent apex and the axis of the primary canine, Ax axis indicated that the canine was distally located but not in close relation to the root of the first premolar. In all cases observable, this distance diminished from the first to the second radiographs. These changes in distances indicate anterior movement of the ectopic canine. In one case where the crown had a facial appearance (case 11, Table 2), the canine moved anteriorly during 36 months, and the angle diminished, resulting in an upward movement.

The angulation: It also changed during the observation period in most cases to a direction pointing more upward. This is what appeared in case 11 (Tabel 2), where the angle between the axis of the permanent and primary canines diminished from 29.8 degrees to 13.3 degrees, indicating an upward movement. In case 15, the same was observed (not measured) on orthopantomograms after 12 months.

Specific comments: One interesting finding is the initial maturity of the ectopic canines in the bilateral case 11. These canines initially had a bilateral maturity index or close to 0, meaning that only the crown had formed. The crowns was tilted mostly in the individual’s left side. From this initial tilted position, the canine erupted ectopically downwards. This was not what appeared int he right side of the individual. It is obvious that the ectopic tilted position of the crown can predict ectopic eruption.

Anterior initial site

The results are illustrated in Table 3 and Fig. 5.

Table 3 Unilateral ectopia of mandibular permanent canines/Initial site, anteriorFig. 5

Overview of unilateral ectopic permanent mandibular canine (Case 16) with the orthopantomogram flipped horizontally to the left, so that the ectopic canine appears on the right side. The canine was initially anterior located compared to the axis of the primary canine (Ax), presented in Table 3. This case is documented before orthodontic treatment and after orthodontic treatment had started. The initial position of the ectopic canine is between the permanent lateral and permanent central mandibular incisors. The primary canine on the left side has been extracted and the orthodontic treatment had not been completed

One case (case 16) belongs to this group, as demonstrated in Table 3. The first orthopantomogram confirmed the onset of formation of the permanent canine anterior to the primary canine axis Ax. The angle between the permanent and primary canines was 16.9, which indicated that the permanent canine had the ability to erupt toward the occlusal plane. The primary canine was extracted, and an orthodontic appliance inserted. Radiographs after orthodontic treatment did not exist.

Similarities/differences between groups

When the unilateral and bilateral cases were compared, the following can be concluded:

1.

Ectopia of the permanent mandibular canine is diagnosed earlier in bilateral cases than in unilateral cases.

2.

The position of the apex from the posteriorly located unilateral ectopic canine is located further posterior, compared to the same distance in bilateral cases.

3.

The crown morphology often changes during the eruption period in both groups.

4.

Extraction of the primary canines occurs in the bilateral group, but seldom in the bilateral group.

5.

Number of orthopantomograms: a greater number of orthopantomograms are taken for each child in the bilateral group, compared to the unilateral group.

6.

Curved root morphology appears only in the bilateral group.

7.

Canine eruption movements: There seems to be two different patterns in canine eruption. Canines moving upward have a more stable location compared to the first premolar, while canines moving downward move away from the first premolar. Furthermore, there seems to be an association between permanent crown appearance and eruption directions and a striking difference in the eruption pattern in the right and left sides in the bilateral cases. The left side has more eruption deviations compared to the right side.