The objective of this study was to evaluate the 3-dimensional changes in alveolar bone morphology after traction of buccally vs palatally unilateral maxillary impacted canines (MIC).
Following a split-mouth model, 27 cone-beam computed tomography images of unilaterally MIC (14 palatally and 13 buccally) and 27 contralateral unimpacted controls were obtained before and after traction using nickel-titanium closed-coil springs and a rigid anchorage appliance. Alveolar bone height and width were measured in the axial, coronal, and sagittal slides by 3 calibrated orthodontists, taking into account the impaction characteristics. A t test was used to compare the 2 groups, and a paired t test was applied for intragroup comparisons (both sides). A multiple linear regression model was used to evaluate the influence of the predictor variables on alveolar bone dimensional changes.
The alveolar height showed a significantly greater decrease in palatally MIC (2.09 to 2.79 mm) than buccally MIC (0.28 to 0.57 mm) ( P <0.05) for all surfaces. However, the alveolar width increased similarly in both groups up to 1.36 mm. In general, the affected side had a more significant height loss and greater increases in alveolar width than the nonaffected side. Regression analysis indicated that buccally MIC and age decreased alveolar changes, whereas female sex increased alveolar changes ( P <0.05).
MIC traction with nickel-titanium closed-coil springs and heavy anchorage induces significant 3-dimensional changes in alveolar bone characterized by alveolar bone height decreases and cervical alveolar bone width increases. The height decrease is greater in palatally than in buccally MIC.
Alveolar bone dimensions after unilateral impacted canine traction were compared.
Buccally vs palatally maxillary impacted canines were assessed.
Nickel-titanium closed-coil springs with a heavy anchorage was used for orthodontic traction.
Palatally impacted canine traction showed a greater decrease in alveolar bone height.
The alveolar width similarly increased in both groups.
The cervical alveolar width increased on the impacted side of both groups.
Orthodontic-surgical traction of maxillary impacted canines (MIC) is a complex treatment and may have consequences on the alveolar bone and roots of the involved teeth. The evaluation of alveolar bone changes after traction of impacted teeth helps to explain the therapeutic limits of the orthodontic dental movement considering the concepts of movement “with the bone,” “within the bone,” and “through the bone.” ,
The extrusive traction forces have an action/reaction effect that acts on the enamel-cement complex of dental roots and leads to important changes in the alveolar bone, including bone loss, dehiscence or cortical fenestrations, and gingival recession. These changes can be observed in both the impacted canine and adjacent teeth. , The buccolingual, vertical, and anteroposterior position, associated with the severity of the MIC, may increase the treatment time, its complexity, and the periodontal sequelae of the traction.
Changes in the movement pathway may be different in palatal vs buccal traction of MIC. Periodontal damage has been shown to be more severe in palatally displaced canines and is usually associated with more aggressive surgical procedures, exposing the root at the cementoenamel junction level. In contrast, Parkin et al demonstrated that the traction of palatally displaced canines generates an irrelevant clinically periodontal affection, whereas buccal traction has been reported to represent a periodontal challenge that reduces the level of the attached gingiva and the width of the alveolar and cortical bone.
Most studies concerning bone changes have been performed using 2-dimensional (2D) intraoral x-ray periapical and panoramic images. These images have limitations, particularly in the anterior region, because of midsagittal over-projection. , Cone-beam computed tomography (CBCT) technology overcomes these limitations, allowing the accurate quantitative and qualitative evaluation of changes in bone height, alveolar width, and cortical thickness in complex situations. , However, no studies have compared the effects of both types of MIC traction on alveolar bone 3-dimensionally with CBCT.
Different alternatives have been described for MIC traction, including the use of metallic chains and ligatures, elastomeric chains, bent loops, and modified hooks. To protect soft tissues and adjacent teeth, the use of rigid customized palatal anchorage and traction with nickel-titanium closed-coil springs (Ni-TiCCS) has been proposed as a treatment alternative. Thus, MIC traction can be controlled in the orthogonal x-, y-, and z-axes.
Some studies have evaluated the alveolar bone changes associated with the traction of unilateral MIC using 3-dimensional (3D) images, without contrasting the location from which the MIC was tractioned. , , , In addition, a comparison of alveolar bone changes after traction of buccally vs palatally unilateral MIC is required, which would be useful to provide important information to clinicians for treatment planning and prognosis. Therefore, the purpose of the present study was to compare the dimensional changes in alveolar bone after traction of buccally vs palatally unilateral MIC and to compare the changes between impacted and nonimpacted contralateral canines on CBCT images.
Material and methods
This retrospective, longitudinal, split-mouth model study was approved by the Ethics in Research Committee of the Universidad Científica del Sur, Lima, Perú (Approval no. 00008). CBCT images of 27 patients (15 women and 12 men aged between 13 and 39 years) with unilateral MIC were obtained before (T0) and after (T1) canine traction. Two groups were defined regarding the type of impaction, with 14 MIC located as palatal and 13 as buccal. In addition, the nonaffected side was evaluated as a control. The CBCT scans were selected from a population of patients with a MIC diagnosis and treated by the same orthodontist (G.A.R.M).
The sample size was calculated considering 80% study power with a significance level of 0.05 (95% confidence level) to obtain a significant difference between groups of 2 mm (buccally MIC = 2.5 mm vs palatally MIC = 0.5 mm) on alveolar buccal height using a standard deviation of 2 mm (buccally MIC) vs 1.5 mm (palatally MIC), which was obtained in a previous pilot study and whose data were included in the final study. A minimum sample size of 13 was determined with the use of OpenEpi software ( openepi.com/SampleSize/SSMean.htm ).
The inclusion criteria consisted of patients of both sexes, older than the age of 12 years, with unilateral MIC, either buccal or palatal, treated with the same orthosurgical traction technique. The exclusion criteria were subjects with syndromes or craniofacial deformities, endoperiodontal lesions, previous orthodontic treatment, history of maxillary surgery or dentoalveolar trauma in the maxillary anterior teeth.
Some demographic data, MIC characteristics (eg, alpha angle, sector and height of impaction), and basic 2D diagnostic data were obtained from the clinical and radiographic registers. CBCT images were obtained at (T0) and (T1), defining T1 as the moment when the MIC reached the occlusal plane and traction was ended.
The measurements obtained from the CBCT images were performed by 3 trained and calibrated orthodontists (G.A.R.M, L.E.A.G, and Y.A.R.C). The intra- and interobserver agreement in location and sector of MIC was evaluated with a kappa coefficient achieving values >0.9. To evaluate the intraobserver reliability regarding the height and width change measurements, the same examiner (G.A.R.M) re-evaluated the 30% of the sample, randomly selected, after a 30-day interval. The data were analyzed with the intraclass correlation coefficient, which also provided values >0.9. In addition, the random error, estimated by the Dahlberg formula, was <1 mm.
The location of each unilateral MIC was defined as buccal or palatal following clinical criteria and CBCT axial section evaluations. The clinical criteria were (1) prominence of the MIC over the mucoperiosteum; (2) in the axial view, canine appearance over the buccal or palatal cortical region; (3) MIC crown positioned over the buccal or palatal region of the lateral incisor root; and (4) surgical access according to the surgeon.
CBCT scans of all patients were obtained with PaX-Uni 3D equipment (Vatech, Hwaseong, South Korea) set at 89 kVp; 4.7 mA; 0.125-mm voxel size; scan time, 15 seconds (mean), and field of view of 8 × 8 cm 2 . Digital Imaging and Communications in Medicine images were analyzed with 3D software (version 11.8; Dolphin Imaging and Management Solutions, Chatsworth, Calif) using multiplanar and 3D reconstructions. The panoramic images derived from CBCT were used to determine the impaction sector according to Ericson and Kurol. Five sectors were considered. Sector 1 was the cusp tip of the MIC located between the mesial aspect of the first premolar to the distal aspect of the lateral incisor. Sector 2 was the cusp tip of the MIC located between the distal aspect of the lateral incisor and the long axis of the lateral incisor. Sector 3 was the cusp tip of the MIC located between the long axis of the lateral incisor and the mesial aspect of the lateral incisor. Sector 4 was the cusp tip of the MIC located between the mesial aspect of the lateral incisor and the long axis of the central incisor. Sector 5 was the cusp tip of the MIC located between the long axis of the central incisor and the interincisor midline. The impaction alpha angle was defined as the angle between the long axis of the MIC and the interincisal midline, and the canine height was measured as the perpendicular distance from the cusp tip of the MIC to the incisal plane ( Fig 1 ).
Sagittal, coronal, and axial sections were evaluated using the same software (Dolphin Imaging 11.8). Using the multiplanar reformation, we identified the vertical axis located in the middle of the canine alveolar space, delimited between the lateral incisor and the first premolar. This axis was also centered on the deciduous pulp conduct axis, when present at T0, or on the pulp conduct of the permanent canine at T1 (at the level of the cervical bone crest, as a reference). This procedure allowed rotations in the 3 planes before the measurements ( red line , Figs 2 and 3 ). Palatal and buccal and mesial and distal heights were measured from the alveolar crest to the nasal floor on the sagittal and coronal views, respectively. In the sagittal view, the buccopalatal widths were measured at 3 levels (cervical, middle, and apical) every 6 mm from the alveolar crest. In the axial view, the buccopalatal cervical widths were measured mesially (proximal to the lateral incisor) and distally (proximal to the premolar) to the canine at the level of the alveolar ridge. All measurements were performed for the MIC and the control canine at T0 and T1 .
All patients were treated by an expert and trained orthodontist following the same treatment protocol (G.A.R.M). The biomechanical sequence of orthodontic treatment followed a rigorous protocol in all subjects. Fixed orthodontic appliances with 0.022 × 0.028-in (Synergy; Rocky Mountain Orthodontics, Denver, Colo) and copper nickel-titanium (Ormco, Glendora, Calif) 0.016 × 0.022-in archwires were used. The deciduous canine in the impaction side was always present during the beginning of the mechanics. Thus, once the anterior and posterior segments were aligned and leveled, the space preparation for the MIC was performed with 0.012 × 0.045-in open coil springs (Rocky Mountain Orthodontics). One month before surgery, the rigid anchorage device (1.1-mm or 1.2-mm stainless steel, Dentaurum, Ispringen, Germany) associated with a palatal acrylic button, and with occlusal-palatal-buccal stepped extensions distal to the lateral incisor and on the proximal sides of premolars and molars (performed with a 0.028-in wire), was cemented. The buccal extensions protect the tissues and avoid immersions of the Ni-TiCCS in the soft mucoperiosteal tissue. Ni-TiCCS 0.010 × 0.036-in and of 8 and 13 mm (Dentos, Daegu, Korea) were used to provide 100-150 g of force when they were activated for transalveolar traction of the MIC ( Fig 4 ).
A 0.017 × 0.025-in stainless steel archwire, passively placed and distally cinched to the most distal molar, was used before traction for maxillary arch consolidation. A closed surgical technique was performed in all patients with an individualized osteotomy that never exceeded the MIC cementoenamel junction. , , , Before the Ni-TiCCS fixation, an absolute transsurgical isolation was performed. The activation was performed immediately after the spring fixation and individualization of the anchorage ( Fig 5 ), and it was maintained during traction (6-7 mm every 6 weeks). Four to 6 months after the initiation of traction, the anchorage and traction springs were removed, and the MIC was leveled. Then, the finalization phase was initiated.
A new CBCT was taken (T1) to evaluate the 3D changes in the root and alveolar bone and to visualize the consequences of the traction on MIC and the nonimpacted teeth after the end of MIC traction. This decision was adopted according to the as low as reasonably achievable principle, international guidelines and is supported by evidence-based science. ,
The statistical analyses were performed using SPSS Statistics for Windows (version 19.0; IBM Corp, Armonk, NY). Descriptive statistics of height and width changes in millimeters were calculated for both groups, palatally and buccally MIC. Data normality was assessed with the Shapiro-Wilk test. The Independent t test or Mann-Whitney U test was used (depending on the data normality) to compare height and width changes between groups (buccally vs palatally unilateral MIC groups), and the paired t test or Wilcoxon signed rank test was used (depending on the data normality) to compare the affected vs the nonaffected sides in each MIC group. Finally, multiple linear regression analyses were applied only to the outcome variables that fulfilled the assumptions of normality and homoscedasticity to evaluate the influence of each variable on height and width changes. An initial regression analysis with all predictor variables followed by a second regression analysis with only predictor variables showing P values smaller than 0.25 was performed (overfit method). Statistical significance was set at 0.05 for all statistical tests.
The age and sex distribution of the sample and MIC characteristics by groups are summarized in Table I . In addition, the traction time in months (palatal, 5.71 ± 1.06; buccal, 5.46 ± 1.26) was similar between groups ( P = 0.579). The palatally MIC group showed significantly higher impaction than the buccally MIC group. The MIC was mainly located in sectors 3, 4, and 5 in both groups (78% of the sample; Table II ).
|Impaction type||Alpha angle|
|Impaction type||Impaction height|
|Impaction type||Traction time|
|Type of impaction||Impaction sector||Total||P|
The alveolar height changes (T0 − T1) showed statistically significant differences between the groups (buccally vs palatally unilateral MIC groups) for all measurements. The palatally MIC height changes ranged from 2.09 to 2.79 mm, whereas the buccally MIC height changes ranged from 0.28 to 0.57 mm. Otherwise, the alveolar width changes were not statistically significantly different between groups ( Table III ).
|Measure||Impacted canine position||n||Mean||SD||P||Mean difference||95% CI|
|Lower limit||Upper limit|
|Palatal height changes||Palatally||14||2.09||2.64||0.034 ∗ , †||1.81||0.04||3.59|
|Buccal height changes||Palatally||14||2.52||2.34||0.011 ∗ , †||1.95||0.33||3.58|
|Mesial height changes||Palatally||14||2.76||2.95||0.019 ∗ , ‡||2.37||0.42||4.31|
|Distal height changes||Palatally||14||2.79||2.22||0.006 ∗ , ‡||2.32||0.73||3.92|
|Cervical width changes||Palatally||14||−1.36||1.14||0.836 ‡||−0.1||−1.04||0.85|
|Middle width changes||Palatally||14||−0.07||2.23||0.274 †||−0.86||−2.51||0.78|
|Apical width changes||Palatally||14||−0.14||2.45||0.262 ‡||−0.99||−2.75||0.78|
|Mesial width changes||Palatally||14||−0.74||1.02||0.328 ‡||−0.39||−1.17||0.41|
|Distal width changes||Palatally||14||−0.76||0.99||0.063 ‡||−0.64||−1.32||0.04|