Original Article
Three-dimensional changes in root angulation of buccal versus palatal maxillary impacted canines after orthodontic traction: A retrospective before and after study

https://doi.org/10.1016/j.ortho.2021.04.003Get rights and content

Summary

Introduction

The aim of this study was to three-dimensionally compare the root angulation changes after orthodontic traction of buccally versus palatally maxillary impacted canines (MICs).

Material and methods

This retrospective study included patients from a private dental office of both sexes, older than 12 years, with at least one unilateral or bilateral buccal or palatal MIC, no loss of permanent teeth, with complete apical closure at the beginning of traction, and with CBCTs taken at pretreatment (T0) and after orthodontic traction (T1). The sample was divided in two groups according to their impaction site: buccal versus palatal. In all the scans, the MIC was segmented and the root angulation changes after traction were evaluated. The assessment included the sigma angle (projected on the XZ plane or coronal tomographic view), the delta angle (projected on the XY plane or axial view) and the epsilon angle (projected on the YZ plane, or sagittal view). Intragroup comparisons were performed with Wilcoxon signed-rank tests. Intergroup comparisons were performed with t-tests or Mann-Whitney U tests. Finally, the influence of MIC characteristics on the measured angles were evaluated with multiple linear regression analyses (α = 0.05).

Results

Thirty-three patients (16 men, mean age: 20.38; 17 women, mean age 18.37) with forty-five orthodontically treated MIC (19 buccal versus 26 palatal) were finally included. The palatal MICs showed greater mediolateral uprighting than the buccal MICs, root displacement towards the midsagittal plane, as demonstrated by the sigma angle (palatal group: 37.58 ± 15.08°; buccal group: 29.17 ± 31.15°; P = 0.164) and delta (palatal group: −76.90 ± 26.55°; buccal group: −30.56 ± 41.67°; P < 0.001) angle changes. The buccal MICs showed greater anteroposterior uprighting, anterior root displacement, as demonstrated by the epsilon angle (palatal group: −4.63 ± 12.37°; buccal group: −25.96 ± 17.79°; P < 0.001).

Conclusions

Mediolateral and anteroposterior root angulation show significant differences after traction between buccal and palatal MICs. Palatal MICs showed greater medial root displacement while buccal MICs showed greater anterior root displacement. This condition should be considered for better planning of traction and orthodontic finishing.

Introduction

Maxillary canine impaction (MIC) is the second most frequent impaction anomaly after the third molars [1] with a palatal/buccal impaction ratio ranging from 3:1[2] to 6:1 [3].

Its treatment requires a demanding biomechanical planning, characterized by extrusive movements associated with difficult angulation control. The factors to be considered during treatment planning are directly related to the impaction condition (buccal, palatal, bicortical).

During traction, the intraosseous positional changes of the MIC will depend on the magnitude, direction and point of application of the forces used, considering its initial impaction position. These aspects might influence the root position of the MIC at the end of traction. The uncertainty about the final position of the root is a common aspect in the traction of impacted teeth [4] and can influence the orthodontic completion process of one case.

Some studies have evaluated the root position pretreatment of buccally, palatally [5] and bicortically MICs on Cone Beam Computed Tomography (CBCT) [6] and panoramic radiographs [7]. Another study [8] described the root morphology with pre-traction CBCT, evaluating only palatally MIC. Shin et al. [9] found that the impacted and labially displaced canines tilt toward the midsagittal plane with traction, but they did not study the behaviour of palatally impacted canines. Zeno et al. [10] in a finite element analysis reported a great initial root inclination movement produced by traction on palatal MICs due to the different levels of root stress distribution from different types of forces. They did not include in their study buccal MICs or angular results at the end of the traction.

High accuracy and versatility of CBCT in root evaluations using segmentation procedures have been reported [11], [12], [13]. Nevertheless, the use of these procedures for the evaluation of treatment changes after MIC traction has been scarcely covered in the literature. Migliorati et al. [14] evaluated two traction techniques on a MIC sample, but did not compare buccal and palatal conditions. This comparison would be useful to improve the biomechanical planning of MIC traction in order to prevent damages on neighbouring anatomical structures and improve the chances of obtaining a favourable root angulation after traction for a more efficient orthodontic finishing phase. For this reason, the purpose of this study was to three-dimensionally compare the changes in root angulation after orthodontic traction of buccally versus palatally MICs, using 3D volumetric models derived from CBCT.

Section snippets

Materials and methods

This retrospective study was approved by the Ethics in Research Committee of the School of Dentistry of Cientifica del Sur University, Lima, Peru (approval number: 00007).

Patients with MIC were selected from the radiographic records of a private dental office (GARM), and divided into 2 groups according to their impaction site: buccal (n = 19) and palatal (n = 26). The selection criteria included patients of both sexes, older than 12 years, with at least one unilateral or bilateral buccal or palatal

Results

Thirty-three patients (16 male, mean age: 20.38y, min: 12y, max: 39y; 17 female, mean age: 18.37y, min: 13y, max: 36y) with forty-five orthodontically treated MIC were included. The way of obtaining the sample is scrutinized in the following flowchart (figure 1). The palatally MICs group showed significantly greater maxillomandibular protrusion (mean difference SNA = −4.26, 95% CI: −7.19 to −1.33, P = 0.005; mean difference SNB = −5.21, 95% CI: −7.97 to −2.45, P < 0.001), skeletal sagittal discrepancy

Discussion

The CBCTs used in the present study were obtained before and after orthodontic traction, when the MIC reached the occlusion plane. The second CBCT was taken to assess possible sequelae that MIC traction might have produce on neighbouring structures and on the root of the same canine because of the high degree of difficulty that this procedure represents, following the ALARA protocol [31].

The pretreatment characteristics could not be controlled because they were inherent to the patients of each

Conclusions

Mediolateral and anteroposterior root angulation show significant differences after traction between buccal and palatal MICs. Palatal MICs showed a greater medial root displacement while buccal MICs showed a greater anterior root displacement. These conditions must be taken into account during the finishing phase of orthodontic treatment to achieve an adequate MIC final angulation and position in the maxillary arch.

Although the MICs traction time was similar in both groups, the total treatment

Disclosure of interest

The authors declare that they have no competing interest.

Contributions

YARC and GARM contributed in the study conception and data collection.

LEAG contributed in the study conception and statistical analyses.

AADC contributed in data checking and manuscript draft.

GJ, LC, ACR, and MY contributed to scientific revision.

HLDDS contributed to research supervision.

All authors read and approved the final version of the manuscript.

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