This case series report included three patients diagnosed with bilateral canine impaction, including five bicortically maxillary impacted canines and one buccal impacted canine. The patients or their parents, when necessary, provided informed consent before treatment. All cases were treated by one well-trained orthodontist (G.A.R.M) in his private practice from Bogotá, Colombia.
The impacted canines were initially diagnosed using panoramic radiographs. Then, CBCTs were used to carefully study the cases. Canine impaction was evaluated in the sagittal, coronal, and axial sections. The impaction sector according to the Ericson and Kurol classification was evaluated in the sagittal section . The α and β angles and the impaction height in millimeters were evaluated in the coronal section as diagnostic criteria. The location of the impacted canines (bucco-lingual position) was evaluated in the axial section to assess the position of the crown relative to both cortical bones. The characteristics of the impacted canines in the three patients are described in Table 1.
Case 1 was a 19-year-old female with an Angle class I malocclusion and a class I skeletal relationship. The impaction sector on both sides was defined as sector 5 according to the Ericson and Kurol classification , and both impacted canines were bicortically located. The right canine had an α angle of 62.20° at 14.3 mm from the incisal plane, which caused severe resorption of the roots of the central and lateral incisors. The left canine had an α angle of 52.10° at 12.6 mm of the incisal plane (Table 1) (Fig. 1). Case 2 was a 36-year-old male with an Angle class I malocclusion and a class I skeletal relationship. The right canine was located in sector 4 with an α angle of 44.8° at 9.3 mm from the incisal plane, which caused severe resorption of the roots of the central and lateral incisors. The left canine was placed in sector 5 with an α angle of 46.9° at 10.4 mm of the incisal plane and demonstrated resorption on the central and lateral incisors. The locations for both impacted canines were bicortical (Table 1) (Fig. 2).
Case 3 was a 13-year-old female with an Angle class I malocclusion and a class I skeletal relationship. The impaction sector on the right side was classified as sector 3 and on the left side was defined as sector 2 according to the Ericson and Kurol classification . The right impacted canine was bicortically located with an α angle of 48.9° at 10.9 mm from the incisal plane, which caused severe resorption of the roots, mainly on the lateral incisor. The left impacted canine was located by the buccal side with an α angle of 22° at 9 mm from the incisal plane, which caused severe resorption of the roots, mainly on the lateral incisor (Table 1) (Fig. 3).
For the three cases, the main objective was to traction all maxillary impacted canines to the occlusal plane and to avoid greater root resorption of the maxillary incisors to ensure an acceptable dental health status. Thus, to avoid further root resorption, we sought to distance the impacted canine from the roots of the upper incisors. The vectors of the coil springs used to pull the impacted canines in the three cases were the same. The first coil spring pulled the canine in the distal direction and the second coil spring pulled the canine in the occlusal direction until traction was completed. At this moment, the central and lateral incisors were not included in the orthodontic mechanics. Once the impacted canine was separated from the incisor root, these teeth were included in the treatment. Then, the traction mechanics with the coil continued.
The deciduous canines were extracted when present (cases 1 and 2). All impacted canines were orthodontically tractioned with the same orthodontic mechanics. NiTi closed coil springs and a single rigid heavy reinforced anchorages were used (Fig. 4). The treatment plan for the three cases included fixed orthodontic appliances with 0.022″ × 0.028″ slot metal brackets (Synergy RMO, Inc., Rocky Mountain Orthodontics, Denver, Colorado, USA), and traction of both impacted canines was obtained using NiTi closed coil springs (0.010″ × 0.036″) that were 13 mm and 8 mm in length and had 150 g of force (Dentos Inc. Daegu, Korea) fastened to vestibular hooks in 0.028″ stainless steel wire. These vestibular hooks were welded to the anchorage appliance that included a rigid palatal acrylic button and an arch over the palatal surfaces of all maxillary teeth present in a 1.2-mm (0.047″) stainless steel wire (Dentaurum, GmbH & Co., Ispringen, Germany). All parts of the anchorage appliance were welded in bands that were cemented to the first permanent molars (Fig. 4). The activations were 4 mm to 5 mm (150 g, approximately) every 4 weeks. The canines were tractioned until they reached the occlusal plane.
The CBCT records were obtained at pretreatment (T0) and after the orthodontic traction of the maxillary impacted canines, when the treated canine reached the occlusal plane (T1), to evaluate any undesirable effect of the traction mechanics on the maxillary teeth. All CBCT scans were obtained using the PaX-Uni 3D (Vatech Co., Ltd., Hwaseong, South Korea) with the following parameters: 4.7 mA, 89 KVp, and exposure time of 15 s. Each field of view mode was 8 cm × 8 cm with a voxel size of 0.2 mm.
For the evaluation of root resorption in all root surface of the maxillary incisors, three-dimensional superimposition of the T1 onto the T0 CBCT scans followed by color-coded map evaluation was performed for each incisor as follows.
First, the maxillary anterior teeth as a group and then each maxillary incisor individually were segmented from the T0 and T1 CBCT scans to create volumetric label maps by using ITK-SNAP version 2.4 (open source software; www.itksnap.org) (Fig. 5). Then, the virtual three-dimensional surface models for each incisor were created from the T0 and T1 volumetric label maps using the 3D Slicer CMF software (open source software; version 4.0; http://www.slicer.org).
For the three-dimensional superimposition (registration), the T1 scan was registered on the T0 scan, and a fully automated voxel-based registration for each maxillary incisor was performed in the 3D Slicer CMF software using, specifically, the root region at the enamel-cement junction level as the best fit reference [23, 28]. It is important to mention that T1 CBCTs were taken after canine traction [20, 21], when patients were still using brackets. To create T1 models, the brackets were removed from the obtained images due to the presence of artifacts that may influence in the superimposition procedure [30,31,32]. Therefore, the superimposition was made on the cervical third of the roots and not in the dental crowns.
This software automatically computes and registers the models. Furthermore, the Hounsfield units used to produce the 3D rendered models used a lower threshold of 250 and an upper threshold of 3000; since small variations in the densities viewed in each CBCT DICOM file can affect the rendered results, a manual correction was performed after reviewing each slice of the region of interest to maintain a high-quality model.
After the registration phase, color-coded maps were used to visually analyze the 3D surface displacement (distance) between the two models [33, 34] using the same software. The 3D distances in millimeters between the two surface models at any point of the root surfaces above the root region used for the registration phase could be evaluated [23, 27, 28].
For this specific study, the color-coded surface distance maps have focused only on root displacements between the T0 and T1 models in millimeters. Shades of red represent the root resorption, shades of green or blue indicate no change. Although some change of blue color in the crowns could be seen, this was a consequence of the difficulty to totally remove the streaking artifact of the brackets and does not represent a change in the dental crown.