Introduction
The objective of this research was to compare the predictive value of panoramic radiographs (PRs) and cone-beam computed tomography (CBCT) scans for the estimation of root resorption, spontaneous eruption of a canine, and time for orthodontic traction.
Methods
CBCT scans and PR images of 88 patients (27 male and 61 female; aged between 11 and 44 years) with 106 palatally displaced maxillary canines were retrieved from a database. Predictive values of several radiographic parameters, including the 3-dimensional angle of the canine, were analyzed using the area under the curve and multiple regression analysis.
Results
The angle to the midline and canine position category had a discriminative ability for root resorption of the central incisors with area under the curve values of 0.63 (95% confidence interval, 0.56-0.79) and 0.83 (95% confidence interval, 0.75-0.91), respectively. PR measurements were not reliable predictors of resorptions, except severe resorptions, of the lateral incisors and the premolars. The measurements describing the position of the canine in relation to the midline could predict spontaneous eruption of the canine, regardless of the imaging method. The canine angle to the midline assessed on CBCT was significantly associated with traction time of the canine, producing the following equation: canine traction time = 49.6 − 0.24 × canine angle to the midline ( r 2 = 0.360).
Conclusions
Only severe resorptions of roots can be predicted with PRs. The use of CBCT is indicated in cases of impacted canines.
Highlights
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Panoramic radiographs have low predictive value for root resorptions.
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Panoramic radiographs and cone-beam computed tomography can predict the spontaneous eruption of impacted canines.
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The 3-dimensional angle of the position of an impacted canine has no added prediction value.
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The angle to the midline on cone-beam computed tomography images can predict the traction time of the impacted canine.
Permanent maxillary canines are the second most frequently impacted teeth, and the prevalence of their impaction is 1%-3% in the general population. Radiological aspects, including the position of the impacted canine and root resorption (RR) of the adjacent teeth, are important factors for selecting a treatment strategy. Several studies have demonstrated the superiority of 3-dimensional (3D) imaging methods in the assessment of impacted canines.
Lately, the SEDENTEXCT project (ie, Safety and Efficacy of a New and Emerging Dental X-ray Modality) was conducted to elaborate scientifically based radiation protection guidelines for cone-beam computed tomography (CBCT). It states that CBCT is indicated when the viability of a lateral incisor is in doubt because of an impacted canine, as evidenced by conventional radiography. Several studies have attempted to predict RRs of the adjacent teeth. The mesiodistal position of the canine , , , canine inclination, and insufficient space for canines were found to be factors involved in lateral incisor RR. In contrast, other studies have not found an association between the mesiodistal position of the canine , , or canine inclinations , , , with RRs of adjacent teeth. In addition to the contradictory results, those studies , only showed a significant correlation between RR and radiographic factors, but they did not demonstrate the predictive value of the 2-dimensional (2D) radiographic parameters for the development of RR.
When choosing 3D imaging over 2D imaging, radiation dose risk and increased expense for society should be weighed against the information obtained. Moreover, additional costs can be incurred when resorptions of the adjacent teeth have not been adequately diagnosed. The following questions should be answered: Is PR reliable enough to predict RRs? Are the sophisticated measurements of the canine position obtained via CBCT images superior to the conventional measurements for predicting spontaneous eruption of the canine and calculating the expected treatment time? The decision-analytic approach provides an investigative alternative to the traditional randomized controlled trial because each patient can have both (or all) of the competing examinations.
Although computed tomography scans provide information about objects in a 3D space, the canine position is usually reported in the orthogonal view, transaxial view, or multiplanar reconstruction in 3 planes.
This study aimed to test the predictive value of different radiographic parameters for the risk of RRs, the possibility of spontaneous eruption of the canine, and the estimation of treatment time. An additional objective was to test the measurement describing the position of a canine in 3D space and whether the 3D angle could provide additional information about treatment efficacy.
Material and methods
This study was retrospective, assessing all of the CBCT scans taken from March 2008 to December 2014 at the Radiological Department of Stomatology at Riga Stradinš University. Before CBCT scanning, a PR was obtained, and an orthodontist assessed the necessity of CBCT scanning after evaluating the PRs for the position of the canine or possible RR of the adjacent teeth. The longest interval between 2 scans was 3 weeks. This study was approved by the ethics committee of Riga Stradinš University. Patients with known or detectable congenital syndromes were excluded from the study. The study sample consisted of 88 patients (61 female and 27 male) whose ages ranged from 11 to 44 years, with a mean age of 16.8 ± 6.1 years. A total of 106 impacted maxillary canines, including 19 bilateral impactions, 33 left unilateral impactions, and 35 right unilateral impactions, were studied.
The PR images were obtained with a Kodak 8000 (Carestream, Croissy-Beaubourg, France). The panoramic image was taken with a high-resolution charge-coupled device sensor, with exposure parameters of 13.8 seconds, 80 kV, and 10 mA. Kodak Dental Imaging Software (Carestream) was used to obtain the measurements via panoramic radiography. The distances were calculated automatically when connecting 2 points of structures of interest. The angles were calculated from the lengths of sides of a triangle using the following equation:
c2=a2+b2−2abcosC.
Three main radiographic predictors believed to correlate with the prognosis for the exposure and alignment of ectopic canines were assessed via PRs: angulation of the long axis of the canine to the midline, vertical distance of the canine crown from the occlusal plane, and mesiodistal position category of the canine cusp tip. The mesiodistal space available for the canine was assigned to 1 of 3 categories modified from Cernochova et al. The available space in the frontal maxilla was assessed clinically according to the following 3 categories: (1) spacing in the maxillary frontal region, (2) alignment of maxillary teeth, and (3) crowding of the maxillary teeth.
The CBCT scans were obtained with an i-CAT Next Generation unit (Imaging Sciences International, Hatfield, Pa). The CBCT images were taken according to a standard protocol with the following parameters: 120 kV, 5 mA, 0.4-mm voxel size, and scan time 20 seconds. The CBCT-generated Digital Imaging and Communications in Medicine (DICOM) files were imported into OsiriX Medical Imaging software (Pixmeo, Geneva, Switzerland). All images were viewed on an iMac 27-inch display with 2560 × 1440 native resolution and Radeon high definition 5750 1 gigabyte ATI graphics (Apple, Cupertino, Calif). OsiriX was chosen because it allows the use of the data set coordinate system that is defined by the scanning technology. Only cases with palatally displaced canines were considered for further analysis.
In the CBCT scans, the coordinates of 2 points (the crown cusp and the apex tip) determining the axis of the canine were recorded on the multiplanar reconstructed images that were generated by the freeware ( Fig 1 ).
The occlusal plane was constructed using 3 points: the tips of the distobuccal cusps of the maxillary first molars and the midpoint of incisors’ incisal edges in the vertical plane projected onto the midline between the mesial edges of the central incisors ( Fig 2 ). The following formula was created to calculate the 3D angle between the occlusal plane and the impacted canine axis:
sinφ=A·x∗+B·y∗+C·y∗A2+B2+C2⋅(x∗)2+(y∗)2+(z∗)2;φ=arcsin{A·x∗+B·y∗+C·y∗A2+B2+C2⋅(x∗)2+(y∗)2+(z∗)2}
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