Introduction
The purposes of this study were to characterize the 3-dimensional position of teeth adjacent to impacted canines and examine whether impaction affects canine development using cone-beam computed tomography.
Methods
Cone-beam computed tomography images of 34 unilateral maxillary impacted canines (12 males, 22 females; mean age, 16.5 years) were collected. Twenty-one canines were palatally impacted (PIC), and 13 were buccally impacted (BIC). Angular measurements of lateral incisors (LIs), first premolars, and the impacted canines positions relative to a 3-dimensional coordinate system and canines’ volume, length, and shape of the roots, were compared between the affected and contralateral control sides. The influence of canine position and severity of impaction was examined. Statistics included the paired t test, Wilcoxon signed rank test, and McNemar test.
Results
In the PIC group, LIs showed significant mesiobuccal rotation (−17.1°), mesial angulation (8.4°), and buccal root torque (5°) and first premolars mesiobuccal rotation (6.1°). In the BIC group, LIs displayed mesiobuccal rotation (−18°) and significant palatal root torque (−5°). The canine volumes were similar in BICs and slightly smaller in PICs. The lengths were shorter in both, but root hooks were more prevalent in BICs. The severity of impaction affected the measured variables.
Conclusions
The differential position of the adjacent teeth is pathognomonic for PIC vs BIC, and impaction seems to affect canine development. The findings provide evidence-based clinical and radiographical clues for early diagnosis of canine displacement and planning the most efficient treatment strategy. In addition, they support timely orthodontic eruption before the development of the apical third of the root.
Highlights
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The position of adjacent teeth is pathognomonic for palatal vs buccal canine impaction.
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Displacement of adjacent teeth is influenced by the severity of canine impaction.
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Impaction seems to affect root development, both length and shape.
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Adjacent tooth positions may provide early diagnostic clues of canine displacement.
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Eruption should be initiated before the development of the apical third of the root.
Aside from third molars, maxillary canines represent the permanent teeth that most commonly show eruptive disorders such as impaction. Maxillary canine impaction has a prevalence ranging from 1% to 3%. The maxillary canines are more often palatally than buccally impacted with a ratio of 6:1 and are more common in females than males in a ratio of 3:1. The buccally impacted canines (BIC) and the palatally impacted canines (PIC) are characterized by different etiopathogenesis. The BICs are more likely related to arch-length deficiency (crowding), whereas the etiology of PICs has been attributed to either genetics or lack of eruption guidance. The genetic theory is based on the association between impacted canines and other genetic dental anomalies found in the same dentitions, such as missing or peg-shaped lateral incisors (LIs), enamel hypoplasia, aplasia of second premolars, and infraocclusion of primary molars. Conversely, the canines may deviate from the typical eruption path because of anomalous maxillary LIs, which develop late and therefore do not provide proper guidance during the critical eruption stages.
The lack of monitoring and the delay in managing the impacted canines can cause different complications such as displacement and root resorption of the adjacent teeth, shortening of the dental arch by teeth drifting, canine ankylosis and resorption, follicular cysts, and recurrent infections. , , These risks have different probabilities. Delayed diagnosis may result in long, complicated, costly, and sometimes painful treatment, which also involves surgical exposure of the impacted tooth.
In contrast, if an incipient canine impaction is suspected early enough, around 9-10 years, preventive or interceptive procedures can be initiated, such as extraction of primary canines , or space gaining through rapid maxillary expansion, molar distalization, or incisor proclination. Such procedures may encourage spontaneous eruption and avoid impaction or decrease the severity of the impaction, thereby facilitating an orthodontic resolution later.
The first step in diagnosis is clinical recognition of the presence of pathognomonic features associated with impacted canines. For example, spaced dentitions with small teeth and anomalous LIs have been extensively linked to PICs, , whereas crowded dentitions with large teeth have been linked to BICs. The next step is the assessment by plane radiographies, such as panoramic or intraoral x-rays, or cone-beam tomography (CBCT) for a more accurate localization.
The relative position of the adjacent teeth to an impacted canine can be another clue for early diagnosis, both clinical and radiographical. Subsequently, when impaction has been confirmed, understanding its influence on the position of the adjacent teeth is crucial for planning the timing of the most efficient mechanotherapy with minimal side effects.
Moreover, when a canine is impacted, its root develops in a restricted environment with the apical root third located against mechanical obstructions such as the floor of the nose or the maxillary sinus cortical bone. Conversely, typically developing canines usually erupt with three fourth of root and may only later develop the final root third without contact and/or proximity to adjacent structures. To date, only 3 studies have focused on this aspect of the impacted canine root development, reporting contradicting results. , ,
Surprisingly, few studies have evaluated the effect of maxillary impacted canines on the 3-dimensional (3D) position of the adjacent LI , and first premolars (FPs). Hence, the present study aimed to characterize the 3D views through CBCT imaging of the LI and FP adjacent to impacted canines, in relation to the severity of canine impaction, and to assess the association between the impaction severity and the development of the canine root.
Material and methods
This retrospective observational study was carried out on pretreatment CBCTs of patients presenting with unilateral maxillary impacted canines. The contralateral normally erupted canines served as controls. The data were obtained from the orthodontic database of the Hebrew University of Jerusalem (Israel) and the University of Campania Luigi Vanvitelli, Naples (Italy). All patients were scanned with 1 of the following CBCT systems: Cranex 3Dx (Soredex Oy, Tuusula, Finland), 3D Accuitomo FPD80 (Morita, Kyoto, Japan), and i-CAT Cone-Beam 3D Imaging (Kavo Dental, Brea, Calif), with 90 KVp; 6.3 mA; 0.2-mm voxel size, scan time, 6.1 seconds; and field of view of no more than 6 cm in height X 8 cm in depth. The initial sample was randomly selected on the basis of convenience sampling, including all consecutively collected CBCTs from October 2018 through February 2020. The calculation of sample size, a mean difference of 5° between the measurements of teeth adjacent to impacted canines and the controls, was considered clinically relevant. A standard deviation of 6.4° was accepted (obtained from a preliminary pilot study) with a 2-sided significance level of 0.05 and a power of 80%. A minimum of 26 sides (13 subjects) was required.
Ethical approval was obtained from the Institutional Review Boards of the University of Campania Luigi Vanvitelli (protocol no. 225) and the Hadassah Medical Organization (HMO-0300-20).
All patients or their parents, if minors, signed an informed consent authorizing the Institutions to use their pretreatment records as part of this research project.
The final sample was selected on the basis of the following inclusion and exclusion criteria. The inclusion criteria were as follows: (1) unilateral impaction of maxillary canine, (2) fully erupted LI and FP, and (3) high-quality CBCTs including both impacted and contralateral normally erupted canines and their adjacent teeth. The exclusion criteria were as follows: (1) diagnosed craniofacial congenital anomalies or syndromes, (2) dental traumatic injuries, (3) missing LI or FP, (4) cysts or other pathologies of the impacted and adjacent teeth, and (5) previous orthodontic treatment.
Dependent variables were as follows: (1) rotation, angulation, and torque of LI and FP adjacent to impacted canines; (2) impacted canine root volume, length, and the presence of deformed roots; and (3) the contralateral normally erupted teeth served as controls.
The following planes of references were defined on CBCT reconstructions ( Fig 1 ) as follows: (1) palatal plane: a horizontal plane, from the posterior nasal spine (PNS) to anterior nasal spine (ANS) as shown by the purple line ( Fig 1 , A and C ), (2) midpalatal plane: a vertical plane, perpendicular to the palatal plane, connecting PNS to ANS as shown by the yellow line ( Fig 1 , B and C ), and (3) vertical plane: a transversal plane, perpendicular to both palatal and midpalatal planes, through ANS as shown by the blue line ( Fig 1 , A and B ).
LI 3D position measurements ( Fig 2 ) were as follows: (1) rotation: the angle between a tangent to the facial contour (from distal to mesial most prominent points) of the tooth and the midpalatal plane in axial views; (2) inclination: the angle between the long axis of the tooth and the midpalatal plane in coronal views; and (3) torque: the angle between the long axis of the tooth and the palatal plane, in sagittal views.
FP 3D position measurements ( Fig 3 ) were as follows: (1) rotation: the angle between a line connecting the most prominent points on the buccal and lingual aspects of the FP cross-sectioned at the cementoenamel junction level and the midpalatal plane, in axial views; (2) inclination: the angle between the long axis of the tooth and the palatal plane in sagittal views; and (3) torque: the angle between the long axis of the tooth and the palatal plane in coronal views.
The lengths and volumes of the canines were assessed by segmenting the canines slice by slice from the CBCT reconstruction. After generating the segmentation of each tooth, the segmentation to 3D models was rendered, and the volume of the whole tooth, including the crown, was calculated ( Fig 4 ). The length of each canine was measured along the long axis from the canine tip to the root apex.
The presence or absence of hooked apices was recorded.
Independent variables were as follows: (1) age and gender; (2) canine localization: BIC or PIC; (3) The severity of impaction: the 3D coordinates (x, y, z) of the tip and root apex were acquired in relation to the 3 planes of reference: transverse (distance to the midpalatal plane), sagittal (distance to vertical plane), and vertical (distance to the palatal plane) ( Fig 5 ). The tips and apices positions were defined by ratios between the impacted and contralateral teeth distance to the reference point, eliminating the influence of individual size; and (4) the dependent variable measurements were compared between 2 subgroups, below and above the median of the independent variables.
Statistical analysis
The measurements were performed with Horos software (version 3; Horos Project, Annapolis, Md). The means, medians, and standard deviations were calculated.
One week after completing the data collection, the CBCTs of 10 patients were randomly selected using online software ( https://www.randomizer.org/ ) to examine the intraobserver reliability. The intraclass correlation coefficient was used to assess the consistency and reproducibility of angular, linear, and volume measurements.
The paired-sample t test was conducted to compare the dependent variables between the impacted canines and contralateral controls groups when the results were normally distributed. The nonparametric Wilcoxon signed rank test was used for not normally distributed data, whereas the McNemar test was considered for binary dependent variables. Calculations were made using IBM SPSS Statistics for Windows, Version 25.0. Armonk, NY: IBM Corp. The significance level was set at 0.05.
Results
The intraclass correlation coefficient values were 0.997 (95% CI, 0.987-0.999) with a mean error of 1.6° for angular measurements, 0.923 (95% CI, 0.724-0.980) with a mean error of 0.5 mm for linear measurements, and 0.973 (95% CI, 0.895-0.993) with a mean error of 19.7 mm 3 for volumetric measurements. Thus, all the measurements were considered highly reliable.
This retrospective observational study allowed the gathering of a sample of 34 subjects with a mean age of 16.5 years (range 10.6-37.1 years) (21 with PIC and 13 with BIC) ( Table I ).
| Variables | Categories | n | % |
|---|---|---|---|
| Age | <14 | 14 | 41.18 |
| >14 | 20 | 58.82 | |
| Sex | Male | 12 | 35.30 |
| Female | 22 | 64.70 | |
| Location | Palatal | 21 | 61.76 |
| Female | 13 | 61.90 | |
| Male | 8 | 38.10 | |
| Right | 9 | 42.86 | |
| Left | 12 | 57.14 | |
| Buccal | 13 | 38.24 | |
| Male | 4 | 30.77 | |
| Female | 9 | 69.23 | |
| Right | 7 | 53.85 | |
| Left | 6 | 46.15 |
Descriptive statistics, including mean and standard deviation, are reported in Tables II and III .
| Variables | Impacted | Control | D | P value | Canine tip | Canine apex | ||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Transversal plane | Sagittal plane | Vertical plane | Transversal plane | Sagittal plane | Vertical plane | |||||||||||||||||||||||||
| <Median | >Median | <Median | >Median | <Median | >Median | <Median | >Median | <Median | >Median | <Median | >Median | |||||||||||||||||||
| Mean | Standard deviation | Mean | Standard deviation | D | P value | D | P value | D | P value | D | P value | D | P value | D | P value | D | P value | D | P value | D | P value | D | P value | D | P value | D | P value | |||
| PICs | ||||||||||||||||||||||||||||||
| LI | ||||||||||||||||||||||||||||||
| Rotation | 40.7 | 13.1 | 57.7 | 12.3 | −17.1 | <0.001∗∗∗ | −19.2 | 0.010∗∗ | −17.5 | 0.033∗ | −20.5 | 0.003∗∗ | −13.2 | 0.065 | −21.2 | 0.004∗∗ | −15.7 | 0.030∗ | −20 | 0.014∗ | −15.4 | 0.025∗ | −14.9 | 0.033∗ | −20.5 | 0.010∗ | −22.7 | <0.001∗∗∗ | −8.8 | 0.167 |
| Angulation | 15.6 | 7.6 | 7.2 | 7.7 | 8.4 | 0.028∗ | 5.0 | 0.260 | 10.0 | 0.042∗ | 6.0 | 0.098 | 11.2 | 0.138 | 7.6 | 0.094 | 7.4 | 0.124 | 8.5 | 0.058 | 6.7 | 0.166 | 5.3 | 0.236 | 10.2 | 0.039∗ | 8.7 | 0.020∗ | 5.4 | 0.418 |
| Torque | 73.8 | 10.4 | 68.8 | 9 | 5.0 | 0.050∗ | 6.5 | 0.257 | 3.0 | 0.172 | 4.2 | 0.287 | 6.0 | 0.214 | −1.5 | 0.586 | 10.9 | 0.008∗∗ | 5.5 | 0.054 | 4.4 | 0.353 | 6.7 | 0.234 | 3.2 | 0.222 | 6.8 | 0.113 | 1.4 | 0.612 |
| FP | ||||||||||||||||||||||||||||||
| Rotation | 79 | 10.7 | 72.9 | 6.3 | 6.1 | 0.050∗ | 5.2 | 0.101 | 4.8 | 0.259 | 5.7 | 0.049∗ | 2.8 | 0.686 | 6.0 | 0.111 | 5.3 | 0.374 | 2.1 | 0.555 | 7.5 | 0.034∗ | 7.3 | 0.043∗ | 1.6 | 0.567 | 5.9 | 0.034∗ | 6.2 | 0.139 |
| Angulation | 89 | 5.5 | 88.6 | 5.4 | 0.4 | 0.805 | 1.7 | 0.488 | −2.3 | 0.373 | −1.1 | 0.610 | −0.1 | 0.484 | −0.7 | 0.831 | 2.0 | 0.846 | 1.9 | 0.214 | −0.2 | 0.766 | 1.3 | 0.634 | −0.7 | 0.777 | −0.1 | 0.947 | 1.2 | 0.685 |
| Torque | 92.3 | 7.6 | 94.9 | 7.3 | −2.5 | 0.141 | 0.6 | 0.851 | −5.3 | <0.001∗∗∗ | −1.1 | 0.645 | −4.9 | 0.019∗ | −2.2 | 0.488 | −2.0 | 0.380 | −0.4 | 0.866 | −3.8 | 0.139 | −2.4 | 0.370 | −2.5 | 0.349 | −0.8 | 0.765 | −4.8 | 0.007∗∗ |
| BICs | ||||||||||||||||||||||||||||||
| LI | ||||||||||||||||||||||||||||||
| Rotation | 44.1 | 11.9 | 62.1 | 14.7 | −18.0 | 0.002∗∗ | −15.9 | 0.010∗∗ | −20.9 | 0.080 | −14 | 0.039∗ | −26.1 | 0.050∗ | −16.4 | 0.052 | −19.6 | 0.036∗ | −8.5 | 0.094 | −22.1 | 0.050∗ | −16.9 | 0.076 | −12.5 | 0.062 | −11.0 | 0.100 | −25 | 0.010∗ |
| Angulation | 11.5 | 14.3 | 8.2 | 5.3 | 3.3 | 0.427 | −3.4 | 0.540 | 11.3 | 0.120 | 1.8 | 0.706 | 5.9 | 0.529 | −0.6 | 0.831 | 1.3 | 0.128 | 1.3 | 0.851 | 8.2 | 0.199 | 11.6 | 0.132 | −2.2 | 0.577 | 3.8 | 0.600 | 2.9 | 0.660 |
| Torque | 53 | 11.2 | 68.7 | 7.1 | −15.8 | 0.002∗∗ | −23.7 | <0.001∗∗∗ | −4.5 | 0.410 | −14.5 | 0.005∗∗ | −18.4 | 0.106 | −18.3 | 0.002∗∗ | −13.3 | 0.071 | −17.5 | 0.042∗ | −13.5 | 0.075 | −8.0 | 0.143 | −24.9 | 0.008∗∗ | −16.5 | 0.010∗∗ | −15.1 | 0.030∗ |
| FP | ||||||||||||||||||||||||||||||
| Rotation | 71.3 | 16.4 | 78.1 | 15.5 | −6.9 | 0.130 | −7.4 | 0.360 | −6.3 | 0.470 | 1.5 | 0.821 | −20.3 | 0.140 | −7.7 | 0.250 | −5.9 | 0.630 | −4.3 | 0.416 | −14.1 | 0.135 | −3.8 | 0.644 | −13 | 0.014∗ | −14.2 | 0.180 | −0.6 | 0.940 |
| Angulation | 91.5 | 7.8 | 89.6 | 6.5 | 1.9 | 0.531 | 5.3 | 0.170 | −1.1 | 0.738 | 1.1 | 0.746 | 3.2 | 0.583 | 4.8 | 0.163 | −1.5 | 0.795 | 4.7 | 0.173 | −1.5 | 0.744 | −5.8 | 0.130 | 10.3 | 0.015∗ | 0.2 | 0.970 | 3.4 | 0.310 |
| Torque | 99.2 | 7.1 | 96.1 | 6.4 | 3.1 | 0.110 | 6.0 | 0.030∗ | 11.8 | 0.430 | 4.1 | 0.289 | 15.8 | 0.437 | 6.4 | 0.020∗ | 11.3 | 0.460 | 6.4 | 0.021∗ | 11.3 | 0.625 | 1.3 | 0.687 | −17.9 | 0.002∗∗ | 15.2 | 0.027∗ | 3.1 | 0.450 |
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