Introduction
The aim of this study was to compare the root resorption (RR) of maxillary incisors after traction of unilateral vs bilateral impacted canines with reinforced anchorage.
Methods
This retrospective longitudinal study included 60 cone-beam computed tomography scans of patients with maxillary impacted canines: 30 scans taken before and 30 taken after orthodontic traction with nickel-titanium coil springs. Two groups were formed according to the impaction condition: 15 with unilateral maxillary impacted canines and 15 with bilateral maxillary impacted canines. Three trained orthodontists made the measurements. Demographic variables, occlusal characteristics, skeletal class, and measurements related to canine impaction were collected from the clinical history, dental models, and radiographs of each patient. RR (mm and mm 2 ) for each maxillary incisor was measured in 3 dimensions. Independent t or Mann-Whitney U tests were used, depending on data normality. Multiple linear regression analyses were used to evaluate the influence of all variables (predictors) on RR (α = 0.05).
Results
RR did not show significant differences between groups in any section ( P > 0.05). No subject had RR greater than 2 mm or 5 mm 2 . The specific influence of some predictor variables varied depending on the type of maxillary incisor.
Conclusions
RR of maxillary incisors after traction of unilateral vs bilateral impacted canines with reinforced anchorage was similar and is not a risk to the integrity of the maxillary incisor root.
Highlights
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Unilateral or bilateral traction of impacted canines with springs was evaluated.
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Incisor roots were measured in 3 dimensions after canine traction.
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Root resorption of incisors of unilateral vs bilateral impacted canines was similar.
Treatment of maxillary impacted canines (MIC) is one of the most complex procedures in orthodontics, because they may have different impaction positions—palatal, buccal, or bicortically centered in the alveolar bone. They may migrate mesially over the central incisors near the middle raphe, and their angle of impaction varies from vertical to horizontal. Likewise, the impaction may be either unilateral or bilateral; this latter condition increases the complexity of orthodontic treatment, its total time, and therefore the possibility of root resorption (RR) of the maxillary incisors. Bilateral impaction is present in 19% to 45% of all patients with impaction.
Conventional treatment of MIC involves special orthodontic biomechanics, which can increase the RR of neighboring teeth, mainly in patients with bilateral canine impaction, because traction is supported on both sides of the teeth as opposed to unilateral impaction. However, a comparison between unilateral and bilateral impacted canines has not been made. To pull a MIC, several intra-arch and interarch mechanisms are used, including nickel-titanium springs, power chains, or wire modifications. In addition, conventional tensile forces are supported on large-caliber archwires in the brackets of the maxillary teeth; which even serves as anchorage for intermaxillary elastics to prevent the side effects of traction. One clinical alternative to prevent further RR is to distance the impacted canine from the roots of the maxillary incisors and then continue with conventional orthodontic treatment. Another possibility to treat MIC that could prevent the side effects of traction is reinforced anchorage, using a heavy buccal archwire with bracket slots (0.019 × 0.025-in stainless steel) with heavy palatal anchorage in the maxillary arch.
The current evidence suggests that orthodontic treatment with uncontrolled forces causes an increase in the incidence and severity of RR, and that heavy forces may be particularly damaging. However, there are few studies in the literature comparing the apical resorption of maxillary incisors resulting from traction of impacted canines, and these studies have been performed with periapical or panoramic radiographs. Their main objectives were different, although they compared apical resorption of maxillary incisors in patients treated with orthodontics, including a small sample with traction of impacted canines. These studies showed a significant increase (approximately 0.6 mm) of apical resorption in the control group, or approximately 1.33 mm from the contralateral side without impaction, or considered it a risk factor for apical resorption of the maxillary incisors. Nevertheless, few studies that were directly performed to evaluate the apical resorption of incisors after orthodontic treatment, including the traction of MIC, found different results from those reported. One of the studies, performed, by Brusveen et al, in patients with unilateral impaction, concluded that there is no significant difference in the apical resorption of incisors between both sides with and without impaction. Lempesi et al, with most subjects in their sample having unilateral impacted canines, concluded the same, but the subjects were compared with a control group without impaction. There are only 2 studies using cone-beam computed tomography (CBCT), by Heravi et al and Silva et al, who concluded that the previous canine disimpaction produces minimal effects of RR, but they only evaluated subjects with palatally displaced canines or unilaterally impacted canines, respectively.
To our knowledge, no studies have compared the RR of maxillary incisors after orthodontic traction of impacted unilateral vs bilateral canines, knowing that this second condition involves different biomechanics, with greater complexity of the treatment and probably greater risk of RR. Likewise, to achieve the traction of a MIC, usually it is necessary to use heavy anchorage and a rigid archwire in the maxillary arch to prevent the undesirable effects of traction. Also, to obtain the canine disimpaction, an ideal force that allows its movement through the bone is needed. This force increases its magnitude in the anchorage and in the archwire when bilateral canines are pulled compared with unilateral impacted canines; therefore, the incisors could have a greater risk of RR in these patients. CBCT is the most accurate, reliable, and nonmagnifying current tool that allows us to know the exact amount of RR of the maxillary incisors, not only apical resorption, but also after orthodontic treatment of MIC. For this reason, the purpose of this study was to compare the 3 dimensional (3D) amount of RR of maxillary incisors after orthodontic traction of impacted canines using reinforced anchorage and coil springs in patients with unilateral vs bilateral impaction. We sought to test the null hypothesis that there is no significant difference in the amount and area of RR of maxillary incisors after orthodontic traction of bilateral vs unilateral impacted canines.
Material and methods
The design of this study was retrospective and longitudinal, specifically a before-and-after study, approved by the Ethics and Research Committee of the Universidad Científica del Sur in Lima, Perú (protocol number 00006). The sample consisted of 30 patients diagnosed and treated in a private orthodontic office (G.A.R.M.), with 60 CBCT images—30 before and 30 after their orthodontic treatment that included traction with coil springs of at least 1 MIC. Two groups were formed according to the type of impaction, unilateral (n = 15) and bilateral (n = 15), in which RR of the maxillary incisors was evaluated (total of 240 incisors). A minimum sample size of 15 participants per group was necessary to provide 80% test power at a significance level of 0.05 to detect an intergroup difference of 0.76 mm in RR of the maxillary incisors, with a standard deviation of 0.85 mm (from a previous pilot study).
Inclusion criteria were patients older than 12 years, with canines unilaterally and bilaterally impacted: palatal, buccal, or bicortically centered. Patients with craniofacial deformities or syndromes, periapical lesions in the maxillary incisors before orthodontic treatment, brackets or maxillary surgeries before the study, or agenesis of a maxillary tooth were excluded.
Full patient records—clinical histories, study models, extraoral and intraoral photographs, panoramic and profile x-rays, and CBCT images before (T0) and after canine traction, exceeding the limits of the alveolar crest to the occlusal plane (T1)—were obtained. Demographic and clinical variables of each patient, including sex, age, Angle classification, skeletal relationship (ANB and APDI ), and characteristics of the impacted canines (condition, sector, angle α, angle β, height, and duration of the traction treatment) were recorded.
Three orthodontists (L.E.A.G., G.A.R.M., Y.A.R.C.) trained in the diagnosis of impacted unilateral and bilateral canines evaluated each tomographic and panoramic radiograph to detail the characteristics of impaction. They had to agree on the diagnosis of impaction sector and position; in case of any discrepancy, the final diagnosis was obtained by consensus. Interobserver calibration was assessed with kappa coefficients. The kappa coefficient values were greater than 0.9. For the quantitative variables, all CBCT measurements were repeated by the same evaluator (L.E.A.G.) after a 30-day interval. Intraobserver calibration was evaluated with the intraclass correlation coefficient until values greater than 0.9 were obtained. Random error of reproducibility was calculated according to Dahlberg’s formula, giving values smaller than 1 mm or 1 mm 2 .
CBCT scans were required to complement the diagnosis of MIC type. The patients were classified according to the number of impactions in unilateral or bilateral cases. Additionally, they were grouped according to their location (palatal, buccal, or bicortical form), defined in axial cuts in which 4 criteria were evaluated: (1) visualization of the MIC and its interpretation, (2) position of the impacted canine crown in relation to a midline drawn between the 2 bone cortical (buccal and palatal), (3) its location in relation to the neighboring lateral incisor, and (4) the surgical approach. CBCT scans of all patients were taken using PaX-Uni 3D (Vatech, Hwaseong, South Korea) set at 4.7 mA, 89 kV(p), voxel size of 0.125, and exposure time of 15 seconds. Each field-of-view mode was 8 × 8 cm 2 . DICOM images were analyzed with 3D software (version 11.7; Dolphin Imaging, Chatsworth, Calif), using multiplanar and 3D reconstructions.
Measurements for this study were made on images synthesized from the CBCT scans. Reconstructed panoramic images were obtained from the computed tomography scans. To determine the impaction sector, we used the classification suggested by Ericson and Kurol. The cusp tip of the canine was localized in 1 of 5 sectors ( Fig 1 ).
Sector 1: the cusp tip of the MIC is between the mesial aspect of the first premolar to the distal aspect of the lateral incisor.
Sector 2: the cusp tip of the MIC is between the distal aspect of the lateral incisor and the long axis of the lateral incisor.
Sector 3: the cusp tip of the MIC is between the long axis of the lateral incisor and the mesial aspect of the lateral incisor.
Sector 4: the cusp tip of the MIC is between the mesial aspect of the lateral incisor and the long axis of the central incisor.
Sector 5: the cusp tip of the MIC is between the long axis of the central incisor and the interincisor median line.
To determine the canine position, Ericson and Kurol used angle α to represent the angle between the interincisor midline and the long axis of canine. We measured angle β between the long axis of the canine and the long axis of the lateral incisor ( Fig 1 ). Canine vertical height was evaluated using the perpendicular distance of the peak of the impacted canine to the occlusal plane formed by a tangent to the incisal edge of the maxillary central incisor and the occlusal surface of the maxillary first molar ( Fig 1 ).
The initial lateral cephalometric radiographs of each patient were obtained with digital cephalometric panoramic equipment (Pax 400C; Vatech). The settings were 90 kV, 10 mA, and 13 to 15 seconds. All cephalometric measurements were performed digitally with the 3D software (version 11.7; Dolphin Imaging), without magnification, at a scale of 1:1. Skeletal relationship measurements were expressed by the ANB and APDI angles, the maxillary sagittal position was determined in the sagittal direction using the SNA angle, and the maxillary length was measured as the distance of from posterior nasal spine to anterior nasal spine.
DICOM images were processed with the same software (version 11.7; Dolphin Imaging). Sagittal, coronal, and axial sections of the maxillary incisors were obtained. For the measurements, the tomographic section was aligned with the longitudinal tooth axis in the coronal and sagittal planes, positioning the incisal edge parallel to the coronal plane in the axial section ( Fig 2 ). Then the root lengths measured in millimeters on the same longitudinal axis from a perpendicular projection to the vestibular cementoenamel junction in the sagittal section or mesial cementoenamel junction in the coronal section up to the vertex of the radicular apex of each incisor were evaluated. The root areas of the incisors, in square millimeters, were then evaluated starting from the buccal or mesial cementoenamel junction, continuing along the contour of the entire root to the palatine or distal cementoenamel junction. ( Fig 3 , A and B ). In the axial sections, the areas of RR were measured at the level of 2 sectors. To define the sectors, the root length of the sagittal section was divided into thirds, and the areas of the cervical and middle thirds in the axial sections were measured ( Fig 3 , C ).
All patients were treated with a strict orthodontic and surgical protocol. A segmental alignment and leveling phase was performed with 0.016 × 0.022-in copper-titanium (Ormco, Glendora, Calif) archwire on metal brackets with a slot size of 0.022 × 0.028 in (Synergy; Rocky Mountain Orthodontics, Denver, Colo) in the incisors and in the premolar and molar regions, always ensuring the permanence of the deciduous canine, if present. The space was prepared with 0.012 × 0.045-in open-coil springs (Rocky Mountain Orthodontics) between the lateral incisor and first premolar on 0.017 × 0.025-in nickel-titanium archwires. Both were indispensable requirements before surgery. Subsequently, a rigid temporary anchor was placed on bands in the permanent first molars with a rigid palatal acrylic button and an archwire over all palatal surfaces of all maxillary teeth in 1.1-mm (0.043 in) or 1.2-mm (0.047 in) stainless steel wire (Dentaurum, Ispringen, Germany) with multiple palatal and occlusal vestibular hooks in 0.028-in wire proximal to the molars and premolars, and distal to the lateral incisors. This anchorage was cemented at least 4 weeks before surgery. Vestibular hooks and extensions of the anchor allowed fastening of the buckles of the nickel-titanium closed-coil springs, 0.010 × 0.036 in, 8 and 13 mm long, with 100 or 150 g of force (Dentos, Daegu, Korea), to perform intraosseous traction transalveolarly, and to prevent the springs from becoming immersed in the attached gingiva and the mucoperiosteum limiting its activation ( Fig 4 ). A passive 0.017 × 0.025-in stainless steel archwire on the brackets of the already aligned and levelled teeth was cinched distally to the last molar involved in the anchorage before traction.
A closed surgical technique in all impacted tooth was used. Exceptionally, an open technique was necessary with surgical window by palatal. A rigorous process of isolation and transsurgical adhesion of the button or buttons with springs fixed to the closed-coil nickel-titanium spring on the vestibular face of each retained canine was performed, and immediately activated from 4 to 5 mm every 4 to 8 weeks until the buccal hooks welded to the anchorage ( Fig 5 ). The deciduous canines, cysts, and supernumerary teeth, among others, were removed in the same surgical procedure. Exceptionally, a premolar was removed. After obtaining traction of the canines, the palatal anchorage was removed; it had protected and stabilized the incisors and premolars. At this time, all necessary procedures to complete the orthodontic treatment were performed. CBCT scans were taken to control the treatment, and the finalization phase was started.
A second CBCT (T1), with the same technical characteristics as the initial one (T0), was requested during orthodontic treatment (end of canine traction) to complete the orthodontic treatment that included canine traction. In the same CBCT, measurements were made of the lengths and root areas of the maxillary incisors in the same sagittal, coronal, and axial sections ( Figs 2 and 3 ). To measure the RR in each incisor, the initial value was subtracted from the final value, and the results were obtained in millimeters and square millimeters in the 3 sections evaluated.
Statistical analysis
The statistical analyses were performed using SPSS software for Windows (version 19.0; IBM, Armonk, NY). Descriptive statistics of RR in millimeters and square millimeters of each maxillary incisor were calculated for both canine groups, unilaterally and bilaterally impacted. Data normality in both groups was determined with Shapiro-Wilk tests. Independent t or Mann-Whitney U tests were used, depending on data normality. Finally, multiple linear regression models to evaluate the influence of each variable on RR of all predictors were used. An initial regression analysis with all predictors followed by a second regression analysis with only predictor variables showing P values smaller than 0.25 was performed for each tooth (overfit method). Statistical significance was set at P < 0.05 for all tests.
Results
The initial characteristics of the sample are shown in Tables I and II . There were no significant differences in most of the variables evaluated between the 2 impaction groups, except for the canine impaction sector ( P = 0.026), with greater difficulty for the subjects in the bilateral impaction group ( Table I ). Canine traction required a longer treatment time (3.4 months) in the bilateral group ( P = 0.002) ( Table II ).
| Variable | Condition | Unilateral | Bilateral | Total | P , chi square |
|---|---|---|---|---|---|
| Sex | Male | 5 | 6 | 11 | 0.705 |
| Female | 10 | 9 | 19 | ||
| Angle malocclusion | Class I | 10 | 10 | 20 | 0.819 |
| Class II Division 1 | 0 | 0 | 0 | ||
| Class II Division 2 | 3 | 2 | 5 | ||
| Class III | 2 | 3 | 5 | ||
| Location of impacted canine (in the unilateral group, the right side was evaluated) | Palatal | 6 | 6 | 12 | 0.198 |
| Buccal | 4 | 5 | 9 | ||
| Bicortical | 0 | 4 | 4 | ||
| Location of impacted canine (in the unilateral group, the left side was evaluated) | Palatal | 3 | 5 | 8 | 0.427 |
| Buccal | 2 | 7 | 9 | ||
| Bicortical | 0 | 3 | 3 | ||
| Impaction sector (in the unilateral group, the right side was evaluated) | Sector 1 | 4 | 3 | 7 | 0.026 ∗ |
| Sector 2 | 0 | 5 | 5 | ||
| Sector 3 | 5 | 1 | 6 | ||
| Sector 4 | 1 | 4 | 5 | ||
| Sector 5 | 0 | 2 | 2 | ||
| Impaction sector (in the unilateral group, the left side was evaluated) | Sector 1 | 0 | 3 | 3 | 0.663 |
| Sector 2 | 1 | 3 | 4 | ||
| Sector 3 | 1 | 4 | 5 | ||
| Sector 4 | 2 | 2 | 4 | ||
| Sector 5 | 1 | 3 | 4 |
| Measurement | Unilateral | Bilateral | Mean difference | Lower limit, 95% CI | Upper limit, 95% CI | P , t test | ||
|---|---|---|---|---|---|---|---|---|
| Mean | SD | Mean | SD | |||||
| Age (y) | 20.67 | 8.75 | 16.8 | 6.41 | 3.86 | −1.87 | 9.6 | 0.179 |
| Duration of traction (mo) | 6.13 | 1.76 | 9.53 | 1.31 | −3.40 | −5.39 | −1.41 | 0.002 ∗ |
| ANB (°) | 2.94 | 2.51 | 4.16 | 2.31 | −1.21 | −3.02 | 0.59 | 0.179 |
| APDI (°) | 82.96 | 4.55 | 81.10 | 6.91 | 1.86 | −2.52 | 6.24 | 0.391 |
| SNA (°) | 85.21 | 4.38 | 84.73 | 5.52 | 0.47 | −3.26 | 4.20 | 0.797 |
| Maxillary length, ANS-PNS (mm) | 47.89 | 3.13 | 47.96 | 5.27 | −0.08 | −3.32 | 3.17 | 0.961 |
| Height of impacted canine, right side (mm) | 9.93 | 2.53 | 11.32 | 4.19 | −1.39 | −4.46 | 1.68 | 0.358 |
| Height of impacted canine, left side (mm) | 11.66 | 2.27 | 12.29 | 5.16 | −0.63 | −5.70 | 4.45 | 0.798 |
| Angle α of impacted canine, right side (°) | 38.24 | 16.17 | 44.76 | 15.41 | −6.52 | −19.79 | 6.75 | 0.320 |
| Angle α of impacted canine, left side (°) | 47.94 | 20.38 | 49.43 | 20.87 | −1.49 | −24.02 | 21.03 | 0.891 |
| Angle β of impacted canine, right side (°) | 33.80 | 13.17 | 43.96 | 18.55 | −10.16 | −24.23 | 3.90 | 0.149 |
| Angle β of impacted canine, left side (°) | 43.76 | 26.94 | 50.17 | 24.40 | −6.41 | −33.51 | 20.70 | 0.625 |
No significant differences were found when the amounts and areas of RR of maxillary incisors were compared between the unilateral and bilateral groups at any section evaluated. No subject had RR greater than 2 mm or 5 mm 2 ( Tables III-V ), except for the RR of the maxillary right central incisor that was significantly greater (0.86 mm) in the unilateral group ( P = 0.023; Table IV ).
| Tooth | Measurement | Unilateral (n = 15) | Bilateral (n = 15) | Mean difference | 95% CI | P | |||
|---|---|---|---|---|---|---|---|---|---|
| Mean | SD | Mean | SD | Lower limit | Upper limit | ||||
| Maxillary left lateral incisor | Root resorption (mm) | 1.19 | 1.06 | 1.55 | 1.00 | −0.36 | −1.13 | 0.41 | 0.348 |
| Resorption area (mm 2 ) | 3.43 | 3.29 | 3.37 | 2.36 | 0.06 | −2.08 | 2.20 | 0.955 | |
| Maxillary left central incisor | Root resorption (mm) | 1.53 | 0.84 | 1.47 | 1.05 | 0.06 | −0.65 | 0.77 | 0.865 |
| Resorption area (mm 2 ) | 4.13 | 3.14 | 3.36 | 3.04 | 0.77 | −1.54 | 3.09 | 0.499 | |
| Maxillary right central incisor | Root resorption (mm) | 1.54 | 1.15 | 1.22 | 0.88 | 0.32 | −0.45 | 1.09 | 0.402 |
| Resorption area (mm 2 ) | 3.54 | 3.09 | 2.49 | 2.49 | 1.05 | −1.05 | 3.15 | 0.314 | |
| Maxillary right lateral incisor | Root resorption (mm) | 1.39 | 1.16 | 0.73 | 0.70 | 0.66 | −0.05 | 1.37 | 0.070 |
| Resorption area (mm 2 ) | 3.40 | 3.42 | 1.71 | 1.74 | 1.68 | −0.34 | 3.71 | 0.100 | |
| Tooth | Measurement | Unilateral (n = 15) | Bilateral (n = 15) | Mean difference | 95% CI | P | |||
|---|---|---|---|---|---|---|---|---|---|
| Mean | SD | Mean | SD | Lower limit | Upper limit | ||||
| Maxillary left lateral incisor | Root resorption (mm) | 1.18 | 0.90 | 1.71 | 1.19 | −0.53 | −1.32 | 0.25 | 0.179 |
| Resorption area (mm 2 ) | 1.83 | 1.84 | 3.07 | 1.93 | −1.24 | −2.65 | 0.17 | 0.083 | |
| Maxillary left central incisor | Root resorption (mm) | 1.37 | 1.03 | 1.33 | 1.01 | 0.04 | −0.71 | 0.81 | 0.902 |
| Resorption area (mm 2 ) | 3.15 | 3.76 | 3.19 | 2.65 | −0.04 | −2.47 | 2.39 | 0.973 | |
| Maxillary right central incisor | Root resorption (mm) | 1.88 | 1.17 | 1.01 | 0.75 | 0.86 | 0.13 | 1.60 | 0.023 ∗ |
| Resorption area (mm 2 ) | 4.79 | 3.82 | 2.99 | 2.73 | 1.80 | −0.68 | 4.28 | 0.149 | |
| Maxillary right lateral incisor | Root resorption (mm) | 1.35 | 0.99 | 1.13 | 1.08 | 0.22 | −0.55 | 0.99 | 0.566 |
| Resorption area (mm 2 ) | 3.43 | 3.27 | 2.22 | 2.05 | 1.20 | −0.83 | 3.25 | 0.237 | |
| Tooth | Measurement | Unilateral (n = 15) | Bilateral (n = 15) | Mean difference | 95% CI | P | |||
|---|---|---|---|---|---|---|---|---|---|
| Mean | SD | Mean | SD | Lower limit | Upper limit | ||||
| Maxillary left lateral incisor | Cervical third | 0.43 | 0.58 | 1.11 | 1.62 | −0.68 | −1.59 | 0.23 | 0.095 |
| Middle third | 0.52 | 0.70 | 1.12 | 1.39 | −0.60 | −1.42 | 0.22 | 0.256 | |
| Maxillary left central incisor | Cervical third | 1.31 | 2.05 | 0.91 | 1.24 | 0.40 | −0.87 | 1.67 | 0.735 |
| Middle third | 1.48 | 2.50 | 1.53 | 1.97 | −0.05 | −1.73 | 1.63 | 0.612 | |
| Maxillary right central incisor | Cervical third | 1.12 | 2.14 | 0.87 | 0.94 | 0.25 | −0.98 | 1.49 | 0.829 |
| Middle third | 1.32 | 2.02 | 1.40 | 2.29 | −0.08 | −1.69 | 1.53 | 0.848 | |
| Maxillary right lateral incisor | Cervical third | 0.61 | 0.86 | 0.53 | 0.73 | 0.08 | −0.51 | 0.67 | 0.949 |
| Middle third | 1.12 | 1.58 | 1.45 | 1.63 | −0.32 | −1.53 | 0.87 | 0.580 | |
Linear regression tests for all quantities and areas of resorption were applied only for predictor variables that could have an effect on the outcome variables and mainly did not show any influence ( P > 0.05). When there was an influence, it varied depending on each incisor ( P < 0.05), and mainly the sex variable influenced the RR ( Tables VI and VII ).
| Predictor variable | ULLI | ULCI | URCI | URLI | ||||
|---|---|---|---|---|---|---|---|---|
| β | P | Β | P | β | P | β | P | |
| Root resorption (mm) | ||||||||
| Constant | 0.194 | 0.312 | 0.052 | 0.489 | ||||
| Sex | 0.862 | 0.069 | −0.653 | 0.528 | −0.494 | 0.074 | −0.276 | 0.325 |
| Duration of traction (mo) | −0.509 | 0.166 | 0.806 | 0.061 | −0.286 | 0.327 | 0.061 | 0.847 |
| Type of impaction | −0.058 | 0.854 | −0.640 | 0.088 | −0.125 | 0.649 | −0.280 | 0.392 |
| Location of impacted canine | 0.808 | 0.185 | −0.428 | 0.609 | −0.440 | 0.290 | −0.089 | 0.836 |
| Canine impaction sector | 0.914 | 0.055 | −0.442 | 0.383 | 0.081 | 0.837 | −0.047 | 0.911 |
| Angle α of impacted canine | −1.867 | 0.023 ∗ | 0.250 | 0.790 | −0.191 | 0.709 | 0.308 | 0.568 |
| Angle β of impacted canine | 2.242 | 0.026 ∗ | −0.662 | 0.606 | −0.219 | 0.567 | −0.067 | 0.854 |
| Height of impacted canine | 0.007 | 0.989 | −0.011 | 0.989 | 0.445 | 0.245 | −0.184 | 0.605 |
| Initial root length | 0.842 | 0.135 | −0.365 | 0.673 | −0.660 | 0.156 | 0.186 | 0.617 |
| r 2 | 0.549 | 0.412 | 0.332 | 0.259 | ||||
| Area of root resorption (mm 2 ) | ||||||||
| Constant | 0.300 | 0.063 | 0.004 ∗ | 0.044 ∗ | ||||
| Sex | 0.610 | 0.135 | −0.761 | 0.070 | −0.560 | 0.017 ∗ | −0.414 | 0.139 |
| Duration of traction (mo) | −0.284 | 0.366 | 0.662 | 0.058 | −0.371 | 0.125 | −0.006 | 0.984 |
| Type of impaction | −0.121 | 0.653 | −0.667 | 0.033 ∗ | −0.064 | 0.773 | −0.351 | 0.242 |
| Location of impacted canine | 0.419 | 0.332 | −0.710 | 0.189 | −0.472 | 0.108 | −0.140 | 0.692 |
| Canine impaction sector | 0.756 | 0.040 ∗ | −0.226 | 0.511 | −0.182 | 0.576 | 0.118 | 0.771 |
| Angle α of impacted canine | −1.532 | 0.017 ∗ | −0.033 | 0.955 | −0.146 | 0.723 | −0.176 | 0.736 |
| Angle β of impacted canine | 1.910 | 0.013 ∗ | −0.333 | 0.670 | −0.332 | 0.286 | −0.029 | 0.934 |
| Height of impacted canine | −0.197 | 0.670 | −0.217 | 0.693 | 0.457 | 0.114 | −0.055 | 0.872 |
| Initial root length | 0.633 | 0.094 | −0.291 | 0.536 | −0.644 | 0.050 | −0.237 | 0.441 |
| r 2 | 0.642 | 0.621 | 0.557 | 0.306 | ||||
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