Palatal canine impaction has a prevalence of 0.8 to 3%1 with a female predilection.2 Although the aetiology has been proposed to arise from a disturbance in the dental lamina with a polygenic, multifactorial inheritance1 or, due to an anomalous or absent lateral incisor,3 the exact cause has yet to be determined. An early diagnosis and timely intervention prevents resorption of the roots of adjacent lateral incisors.4 Using CT images, mid-facial dimensions, specifically nasal width, have been investigated as a possible aetiological factor related to palatal canine impaction but a control group was not compared.5 In addition, facial soft tissue variables were not assessed but these may be relevant and easier for the clinician to evaluate.
There is conflicting evidence regarding the maxillary transverse dimension in patients with a palatally impacted canine.5–9 While maxillary inter-canine (IC) and inter-molar (IM) widths have been reported to be reduced,5–7 others have detected an increase in maxillary arch width.8,9 Similarly, palatal depth has been found to be smaller7 or of minimal difference relative to control subjects,10 while palatal area has been reported to be reduced on the side of the impacted palatal canine.7 A lesser mesiodistal maxillary lateral incisor width, as well as size discrepancies in female patients has also been implicated.11–13 In the light of this evidence, the relevance of these factors remains unclear.
Dental and maxillary arch parameters in a sample of patients presenting with a palatally impacted canine have been compared to control subjects.7,10,14 No study has collectively compared the possible correlations between facial, maxillary arch and incisor dimensions in patients presenting with a unilaterally impacted palatal canine against a control group or has evaluated 3D facial soft-tissue dimensions within these groups.
The aim of the present prospective study in Caucasian adolescents was to identify possible relationships between facial, maxillary arch and incisor dimensions associated with a unilaterally impacted palatal canine. The null hypothesis stated that, ‘in Caucasian adolescents, there were no differences in the relationships between soft-tissue facial, maxillary arch and maxillary incisor dimensions associated with a unilaterally impacted palatal canine compared to control subjects’.
Ethical approval was granted by the local clinical research ethics committee (ECM 4 (
Inclusion/exclusion criteria.
Inclusion criteria | Exclusion criteria |
---|---|
Non-Caucasian subjects or those with cleft lip and palate or craniofacial syndromes | |
Buccal, line of arch or bilateral buccal or palatally impacted maxillary canines | |
One or both maxillary first permanent molars extracted or with a restored mesial surface | |
Restored or carious proximal surface(s) of any of the six maxillary anterior tooth | |
Fractured or damaged study models |
A stereophotogrammetric camera system (www.di4d.com)15 connected to a Dell Dimension 980 personal computer was re-calibrated for each session and images captured using Di3D Capture software (Dimensional Imaging, Glasgow, Scotland, UK). The accuracy of the system was 0.1 mm.16 Following instruction, one operator experienced in 3D image capture, recorded each subject when at rest using the verbal cue recommended by Zachrisson.17 Subjects practiced this twice before each image was taken. The 3D co-ordinates of twelve landmarks were identified from each image (Figure 1A, Table II).18 For each subject, 3D distances and angles were then recorded (Tables II, III).19 To determine the face ratio (face height divided by face width; Figure 1B), 2D facial images were exported from Di3D software and landmarks identified (Paint, Microsoft Corporation, Redmond, Seattle, USA). Facial shape was visually defined using these images as square, tapered or ovoid.20
(A) Facial landmarks and (B) facial ratio showing face height measured from hairline to soft tissue chin, and face width measured from left to right zygion.
Facial Landmarks.
Landmark name | Definition |
---|---|
Midpoint between the eyes (mid) | The halfway distance between exocanthion left and right |
Soft tissue nasion (n) | Point in the midline of both the nasal root and nasofrontal suture |
Exocanthion right (exR) | Outer most point on commissure of right eye fissure |
Exocanthion left (exL) | Outer most point on commissure of left eye fissure |
Pronasale (prn) | Most protruded point of apex nasi |
Subnasale (sn) | Midpoint of angle where lower nasal septum and lips meet |
Alare right (alR) | Most lateral point of the right alar contour |
Alare left (alL) | Most lateral point of the left alar contour |
Alar curvature Right (acR) | Most lateral point in the curved base line of right alar base |
Alar curvature Left (acL) | Most lateral point in the curved base line of left alar base |
Labiale superioris (ls) | Midpoint on upper vermilion border |
Pogonion (pg) | Most anterior midpoint on chin |
3D distances and angles.
3D distances | Definition | 3D angles | Definition |
---|---|---|---|
Distance between exR-exL | Angle between exR-pg-exL | ||
Distance between alR-alL | Angle between s-sn-pg | ||
Distance between acR-acL | Angle between n-pr-sn | ||
Distance between n-pg | Angle between prn-sn-ls | ||
Distance between ls-pg | |||
Distance between ls- mid |
For both the unilaterally impacted palatal canine and control groups, plaster study models were scanned to produce digital images. The following measurements were calculated (R700 and OrthoAnalyzer, 3Shape, Copenhagen, Denmark).
The maxillary right and left canine tip and first molar mesiobuccal cusp tips were identified (Paint, Microsoft Corporation, Redmond, Seattle, USA) to calculate the inter-canine and inter-molar widths, respectively. On the impacted canine side, either the distance halfway between the maxillary lateral incisor and first premolar or the primary canine was marked.
This was calculated using the method by Al-Khateeb et al.7 as the perpendicular distance from a line between the first permanent molars at the gingival level and the maximum depth of the palatal vault.
Using Di3D software (Dimensional Imaging, Glasgow, UK), the palatal area was measured using the area tool.
The mesial and the distal contact points of the six maxillary and mandibular anterior teeth were identified from the occlusal aspect and the anterior Bolton ratio was calculated.
These were classified as square, tapered or ovoid.21
Tooth ratio. ab = crown height; cd = crown width.
These were classified as square, tapered, round, square/tapered or square/round.
This was calculated by dividing crown height by crown width.22
The radiographic position of each maxillary canine was re-confirmed two-weeks after the initial assessment using the entire sample. At the same time interval, intra-examiner reproducibility of landmark identification, measurements and shape assessment were determined by re-assessing 40 (20% of cases) randomly selected facial images and digital models.
Numeric parameters were compared between the groups using general linear models. Age, gender and malocclusion type were included in the models. Data transformations were applied when needed to normalise the residuals. Categorical parameters were compared between groups using Fisher’s exact test (
The sample characteristics are provided in Table IV in relation to the 54 subjects (37 females, 17 males) in each group. There was no significant difference between the groups with respect to age, gender and malocclusion (
Sample characteristics.
Unilateral palatal canine group | Control group | |
---|---|---|
14.5 (1.7) | 14.3 (2.2) | |
54 | 54 | |
Class I | 24 | 24 |
Class II/1 | 8 | 8 |
Class II/2 | 17 | 17 |
Class III | 5 | 5 |
Note: Key: n = numbers.
Facial soft-tissue, maxillary arch and incisor dimensions for the unilateral palatal canine and control groups.
unilaterally palatal canine group | Control group | Mean difference, 95% CI | ||
---|---|---|---|---|
| ||||
Mean, SD (mm) | 87.13 (3.23) | 87.29 (4.25) | -0.17 (-1.61, 1.27) | 0.6645 |
| ||||
Mean, SD (mm) | 31.61 (2.18) | 31.89 (2.51) | -0.28 (-1.18, 0.62) | 0.5314 |
| ||||
Mean, SD (mm) | 18.91 (1.47) | 20.57 (2.57) | -1.66 (-2.46, -0.87) | < 0.0001* |
| ||||
Mean, SD (mm) | 103.12 (6.42) | 103.21 (6.35) | -0.09 (-2.53, 2.35) | 0.7701 |
| ||||
Mean, SD (mm) | 39.55 (3.98) | 40.42 (4.61) | -0.86 (-2.51, 0.78) | 0.1724 |
| ||||
Mean, SD (mm) | 56.66 (3.53) | 55.69 (3.92) | 0.97 (-0.46, 2.39) | 0.1776 |
| ||||
Mean, SD (mm) | 49.04 (2.63) | 48.91 (2.59) | 0.13 (-0.87, 1.12) | 0.6987 |
| ||||
Mean, SD (mm) | 163.01 (4.86) | 162.70 (5.35) | 0.31 (-1.64, 2.26) | 0.7509 |
| ||||
Mean, SD (mm) | 101.91 (5.65) | 103.08 (5.63) | -1.16 (-3.31, 0.99) | 0.3758 |
| ||||
Mean, SD (mm) | 131.96 (9.15) | 131.04 (8.30) | 0.92 (-2.41, 4.25) | 0.5240 |
| ||||
Mean, SD | 1.45 (0.19) | 1.46 (0.08) | -0.01 (-0.06, 0.05) | 0.5409 |
| ||||
Mean, SD (mm) | 30.46 (3.32) | 31.89 (3.36) | -1.44 (-2.71, -0.17) | 0.0186 |
| ||||
Mean, SD (mm) | 48.27 (3.41) | 49.04 (3.83) | -0.77 (-2.15, 0.61) | 0.2876 |
| ||||
Mean, SD (mm) | 14.19 (2.25) | 13.79 (2.33) | 0.40 (-0.48, 1.27) | 0.4705 |
| ||||
Mean, SD (mm2) | 16.43 (2.53) | 16.56 (2.58) | -0.13 (-1.11, 0.84) | 0.4566 |
| ||||
Mean, SD | 79.46 (6.07) | 76.59 (4.60) | 2.87 (0.82, 4.93) | 0.0070** |
| ||||
Mean, SD | 1.93 (0.26) | 1.93 (0.26) | 0.00 (-0.10, 0.10) | 0.9459 |
| ||||
Mean, SD | 1.94 (0.23) | 1.96 (0.27) | -0.02 (-0.11, 0.08) | 0.7879 |
| ||||
Mean, SD | 2.54 (1.06) | 2.59 (0.98) | -0.06 (-0.45, 0.33) | 0.7761 |
| ||||
Mean, SD | 2.70 (0.88) | 2.57 (0.88) | 0.13 (-0.21, 0.47) | 0.3494 |
Notes: *Significant at Bonferroni-adjusted α = 0.0045 **Significant at Bonferroni-adjusted α = 0.01.
Prevalence of facial soft-tissue, maxillary arch and incisor shapes.
Unilateral palatal canine [ | Control [ | ||
---|---|---|---|
| 22 (41) | 12 (22) | |
| 22 (41) | 29 (54) | |
| 10 (19) | 13 (24) | 0.1383 |
| 19 (35) | 11 (20) | |
| 7 (13) | 5 (9) | |
| 28 (52) | 38 (70) | 0.1492 |
| |||
| 4 (7) | 4 (7) | |
| 50 (93) | 50 (93) | |
| - | - | |
| - | - | 1.0000 |
| 3 (6) | 3 (6) | |
| 51 (94) | 50 (93) | |
| - | 1 (2) | |
| - | - | 1.0000 |
| 14 (26) | 11 (20) | |
| 6 (11) | 8 (15) | |
| 25 (46) | 27 (50) | |
| 9 (17) | 8 (15) | 0.8553 |
| 8 (15) | 10 (19) | |
| 7 (13) | 7 (13) | |
| 32 (59) | 33 (61) | |
| 7 (13) | 4 (7) | 0.8189 |
Mean nasal basal width was smaller (1.66 mm, 95% CI: (0.87, 2.46)) in the impacted canine group compared with the control group (
There was no significant difference in inter-canine width, inter-molar width, palatal depth, palatal area or arch shape distribution between the impacted canine and control groups.
The mean anterior Bolton ratio was larger in the impacted canine compared with the control group (2.87, 95% CI: (0.082, 4.93) (
Correlations and
Variable 1 | Variable 2 | Correlation co-efficient | P value |
---|---|---|---|
Eyes distance | Intercanine width | 0.02 | 0.8196 |
Nose width | Intercanine width | 0.13 | 0.3531 |
Basal width | Intercanine width | 0.04 | 0.7812 |
Total face height | Intercanine width | -0.09 | 0.3534 |
Lower face height | Intercanine width | -0.02 | 0.8557 |
Mid-face height | Intercanine width | -0.06 | 0.5110 |
Mid-face angle | Intercanine width | 0.05 | 0.5726 |
Face convexity | Intercanine width | -0.10 | 0.3166 |
Nose prominence | Intercanine width | 0.08 | 0.4022 |
Philtrum depth | Intercanine width | -0.00 | 0.9707 |
Eyes distance | Intermolar width | 0.08 | 0.3852 |
Nose width | Intermolar width | 0.11 | 0.2427 |
Basal width | Intermolar width | 0.15 | 0.1275 |
Total face height | Intermolar width | 0.04 | 0.7185 |
Lower face height | Intermolar width | 0.14 | 0.1627 |
Mid-face height | Intermolar width | -0.03 | 0.7855 |
Mid-face angle | Intermolar width | -0.01 | 0.8873 |
Face convexity | Intermolar width | -0.05 | 0.5992 |
Nose prominence | Intermolar width | 0.13 | 0.1781 |
Philtrum depth | Intermolar width | 0.02 | 0.8416 |
Basal width | Anterior Bolton ratio | -0.12 | 0.2006 |
There were no meaningful correlations between a unilaterally impacted palatal canine and any of the assessed variables, either individually or collectively.
The present prospective case-control study assessed soft-tissue facial, maxillary arch and incisor dimensions in relation to patients presenting with a unilaterally impacted palatal canine. The null hypothesis was rejected on the basis that mean nasal basal width and the anterior Bolton ratio differed significantly between patients presenting with a unilaterally impacted palatal canine compared with a control group. No other differences were found between the groups and no correlation was found between the variables.
Bilateral palatal10,23 or buccal canine impactions were not included due to their different aetiologies.10,23,24 Their exclusion is consistent with previous studies and avoided heterogeneity of the sample, which would have adversely affected the results.5,25 The reliability of radiographic canine localisation using vertical parallax was excellent. Mean 3D landmark identification error was low (0.58 mm), similar to findings of a previous 3D facial investigation.26 Landmark identification errors on digital models along with the errors of measurement and shape assessments were similarly small and lower than formerly recorded.27
In the present study, the severity of unilaterally impacted palatal canines was not determined by cone-beam CT. There were no facial, maxillary arch nor incisor morphological variables excluded. All malocclusion groups were included making the findings able to be generalised for Caucasians. No previous prospective investigation has assessed the individual and collective relationships between facial, maxillary arch and incisor dimensions associated with a unilaterally impacted palatal canine. Bias was minimised by the recruitment of consecutive Caucasian patients presenting with a unilaterally impacted canine with whom comparison was made using prospectively recruited control subjects matched for age, gender and malocclusion and without a unilaterally impacted palatal canine.28
The greater female to male ratio in the unilaterally impacted palatal canine group supported previous findings1 and, as there were no significant differences in baseline characteristics, the males and females were combined and analysed following the protocol of an earlier investigation.7 There was a greater prevalence of Class I malocclusion (44%) cases which is broadly consistent with existing studies.7,25,29 A greater prevalence of palatal canine ectopia, however, has been identified in patients presenting with a Class II division 2 malocclusion.30,31
There was no significant difference in either face shape nor ratio between the groups, although an ovoid or square shape was more common in the impacted canine group. Kim et al.5 found no difference in either mean nasal cavity width nor mean nostril width between palatally and buccally impacted maxillary canines but did not incorporate an untreated control group. In the present study, mean nasal basal width was smaller by almost 2 mm in the unilaterally impacted palatal canine group compared to the control group. Facial soft tissue scanning was conducted in the present study, whereas Kim et al.5 used CT scanning. The means by which a narrower nasal basal width influences the developmental path of the maxillary canine remains to be explored.
No significant dental arch differences were identified between the unilaterally impacted palatal canine and control groups in support of previous results.10,32,33 However, in contrast, the mean intercanine width was not significantly reduced in the impacted canine group.7,32,34 A significantly larger mean anterior Bolton ratio was noted in the impacted canine group compared to the control group.35,36 The mean anterior Bolton ratio in the control group (76.6) was similar to that originally recorded by Bolton.37 Although there were no significant differences between the groups in relation to the tooth ratio analyses, the larger anterior Bolton ratio incorporates crown evaluation of the six maxillary anterior teeth and is not specific to the lateral incisor. Leonardi et al. found a shorter maxillary lateral incisor root associated with a palatally impacted canine, which may be more relevant to the guidance theory.38
No correlation was found between any of the variables assessed in the impacted canine group and the differences identified between groups were small. Consequently, the aetiology of a unilaterally impacted palatal canine would appear more likely to be genetically controlled1 rather than due to facial, maxillary arch or dental morphological anomalies. Future studies should consider the investigation of potential biomarkers for risk factors related to palatal canine ectopia.
Patients presenting with a unilaterally impacted palatal canine had a narrower mean nasal basal width and a larger mean anterior Bolton ratio compared to a control group. The clinical significance of the differences was considered minor. Facial, maxillary arch and incisor dimensions were neither individually nor collectively correlated with a unilateral impacted palatal canine, which may lend support to an underlying genetic aetiology.