In this study, we aimed to analyze the root apex positions of impacted maxillary canines on panoramic radiographs according to their labiopalatal positions and to propose a new panoramic radiographic predictor of impacted maxillary canines.
Paired panoramic films and cone-beam computed tomography images of 104 patients with unilateral impacted maxillary canines were selected. The sector locations of the impacted canine root apices on the panoramic radiographs were compared with the labiopalatal positions of impacted maxillary canines on cone-beam computed tomography. Statistical correlations between panoramic and cone-beam computed tomography findings were examined with the chi-square test.
A statistically significant association was observed between the sector locations of impacted canine root apices and the labiopalatal positions of the canines ( P <0.001). The root apices of labially impacted canines were more frequently located in sector 2 (corresponding to the lateral incisor position), those of palatally impacted canines were more frequently located in sector 4 (corresponding to the first premolar), and those of midalveolus impacted canines were more frequently located in sector 3 (corresponding to the canine).
On panoramic films, the root apices of palatally impacted canines tended toward the root apices of the maxillary first premolars, whereas those of labially impacted canines tended toward the root apices of the maxillary lateral incisors. Therefore, the sector locations of impacted canine root apices on panoramic radiographs could be used for the early prediction of maxillary canine impactions and determination of the labiopalatal positions of impacted canines.
We developed a new predictor of impacted maxillary canines on panoramic film.
The predictor was the root apex position of the impacted canine.
We found an association of root apex position between the panorama and CBCT.
The root apex of palatally impacted canines tended toward that of first premolars.
Maxillary canines fulfill important esthetic and functional roles. Unfortunately, the prevalence of impacted maxillary canines is approximately 1% to 3%, the second highest frequency behind that of third molar impaction. This high frequency can be explained by the facts that maxillary canines have the longest period of development and the longest path of eruption of all teeth, and that a palatally impacted canine appears to be a developmental anomaly with genetic determinants.
Impacted canines can cause various problems such as cyst formation and root resorption of proximal teeth during eruption. In addition, it is difficult to treat an impacted maxillary canine surgically or orthodontically, and the required treatment period is long. Clinicians must carefully observe the eruption process to make an early diagnosis of maxillary canine impaction, eliminate local eruption-obstructing factors, or extract deciduous canines to prevent impaction. Therefore, early diagnosis and careful observation are crucial to the successful treatment of maxillary canine impaction.
Canine impaction can be diagnosed at an early stage using visual examination, palpation, or radiography. Currently, panoramic film, lateral cephalography, posteroanterior cephalography, and cone-beam computed tomography (CBCT) are the radiographic tools of choice for diagnosis. Among these, CBCT can accurately identify and locate the positions of impacted canines; however, the relatively high radiation doses have restricted its use for the early diagnosis of tooth impaction. Therefore, previous studies attempted to identify early canine impactions on panoramic radiographs. Those studies focused mainly on the crown or axial angle of the impacted canine. The crown location can be easily altered by eruption-obstructing factors, whereas the locations of the root apices do not often change. A recent study with CBCT data found that the root apices of impacted canines were generally farther from the arch forms of root apices, compared with those of nonimpacted canines, and that the root apices of impacted canines in the palatal area tended more toward the first premolar root apices, compared with those of other impacted canine groups. Therefore, in this study, we focused specifically on root apices on panoramic radiographs.
The purposes of this study were to analyze the positions of impacted maxillary canine root apices on panoramic radiographs according to the labiopalatal positions of the impacted canines and to propose a new predictor of impacted maxillary canines on panoramic radiographs.
Material and methods
The subjects in this study were selected from among 104 patients who had CBCT (Pax-Zenith3D; Vatech, Seoul, Korea) to localize unilateral impacted maxillary canines after undergoing panoramic radiography and clinical examinations at Pusan National University Dental Hospital between January 2010 and August 2016. The exclusion criteria were systemic disease, odontoma, mesiodens, or cleft lip and palate. The average age of the patients was 13.7 ± 2.8 years (range, 8.9-19.1 years), and the sample included 54 female and 50 male patients. This study was reviewed and approved by the Institutional Review Board of Pusan National University Dental Hospital (PNUDH 2015-028).
A CBCT scanner was used to identify the exact locations of the root apices. The CBCT settings were as follows: tube voltage, 90 kVp; scan time, 24 seconds; tube current, 4 mA; voxel size, 0.3 mm; and field of view, 10 × 8 cm. Using CBCT data, each sample was classified according to the crown location of the impacted canine and specifically with regard to the labiopalatal relationship to yield the following groups: group labial, group palatal, and group middle. Regarding the latter, if the impacted canine crown touched the line between the adjacent lateral incisor and first premolar crown, it was classified into group middle. Group labial included 46 patients (24 with impacted right canines; 22 with impacted left canines). Group middle included 18 patients (9 with impacted right canines; 9 with impacted left canines). Group palatal included 40 patients (18 with impacted right canines; 22 with impacted left canines).
Paired panoramic radiographs (Planmeca, Helsinki, Finland) and CBCT images from the 104 patients were analyzed. The mesiodistal position of the impacted maxillary canine root apex relative to adjacent teeth was classified into a panoramic sector using a modification of the method of Alessandri Bonetti ( Fig ). Specifically, because the location of the lateral incisor or the first premolar can be easily affected by impacted canines, we defined the sector position on the contralateral unimpacted canine site and symmetrically applied that position to the opposite impacted canine site.
Each measurement was performed by 1 investigator (S.-H.K.). To evaluate intraexaminer reliability, data were reobtained after an interval of 1 month. Intraexaminer agreement was evaluated using the Cohen kappa statistic. The correlation between the sector location on the panoramic radiographs and the labiopalatal position on the CBCT images was examined using the chi-square test. An adjusted standardized residual, a measure of the strength of the difference between observed and expected values, was calculated for the purposes of chi-square post-hoc analysis. Also, because the sample size was relatively small and more than 20% of the cells had expected values less than 5, we conducted the exact test and the Monte Carlo test. SPSS software (version 23.0; IBM, Armonk, NY) was used for the statistical analysis.
Of the 104 unilateral impacted maxillary canines evaluated in this study, 46 (44.2%) were impacted labially, 18 (17.3%) were impacted in the midalveolus, and 40 (38.5%) were impacted palatally. Intraexaminer agreement between the panoramic images and the CBCT results was high, with kappa values of 0.824 for sector location and 0.834 for labiopalatal location.
A statistically significant association was observed between the sectors and the labiopalatal positions of the canines ( P <0.001; Table I ). Also, both the exact and Monte Carlo tests showed a statistically significant association between the sectors of the canines and the labiopalatal position of the canines ( P = 0.003). Eight (17.4%) of 46 labially impacted canines were located in sector 2, in contrast to only 1 (2.5%) of 40 palatally impacted canines. Furthermore, 34 (85.9%) of 40 palatally impacted canines were located in sector 4, in contrast to 19 (41.3%) of 46 labially impacted canines. Nine (50.0%) of 18 midalveolus impacted canines were located in sector 3, in contrast to 5 (12.5%) of 40 palatally impacted canines. Adjusted standardized residuals are shown in Table II . Labially impacted canines were more frequently observed in sector 2, palatally impacted canines were more frequently observed in sector 4, and midalveolus impacted canines were more frequently observed in sector 3.
|Impaction position||Sector cases (%)||Total||Chi-square ( P value)|
|Labial||0 (0%)||8 (17.4%)||19 (41.3%)||19 (41.3%)||46 (44.2%)||20.790 ∗ (0.000)|
|Palatal||0 (0%)||1 (2.5%)||5 (12.5%)||34 (85.9%)||40 (38.5%)|
|Midalveolus||0 (0%)||2 (11.1%)||9 (50.0%)||7 (38.9%)||18 (17.3%)|
|Total||0 (0%)||11 (10.6%)||33 (31.7%)||60 (57.7%)||104 (100%)|