Introduction
This research aimed to analyze the prevalence of root dilaceration in buccally impacted canines (BICs) and palatally impacted canines (PICs) with their adjacent teeth based on a retrospective cone-beam computed tomography (CBCT) investigation.
Methods
Pretreatment CBCT images of 145 subjects with unilateral maxillary canine impaction and 145 age- and sex-matched subjects without impaction were used. Prevalence of dilaceration (subclassified to root curvature and apical hook based on severity) in canines and adjacent teeth was determined in CBCT records. The root length of maxillary impacted canines was measured for further morphologic evaluations.
Results
Impacted canines had a significantly higher prevalence of root dilaceration than the control group and compared with the erupted contralateral canines in the experimental group ( P < 0.001 for both). A significantly higher prevalence of root dilaceration was found in adjacent lateral incisors of the PICs subgroup than that of the control group ( P < 0.001). Adjacent premolars had a higher prevalence of dilacerated roots in the PICs subgroup ( P < 0.001) than the control group, but not for the BICs subgroup. Significantly higher prevalence of curvature ( P < 0.001 for both) and hook ( P = 0.008 and P < 0.001, respectively) were found in BICs and PICs roots compared with the control group. Both types of impacted canines had significantly shorter roots than the control group ( P < 0.001 for both).
Conclusions
BICs and PICs have a higher tendency to present root dilaceration and shorter roots. Unlike BICs, adjacent teeth to PICs were more frequently observed to have root dilaceration.
Highlights
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Buccally (BICs) and palatally impacted canines (PICs) were observed with root dilaceration.
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Root dilaceration was more common in adjacent teeth to PICs than BICs.
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BICs had shorter roots than PICs and erupted canines.
Abnormal angulation or curvature formed in the root or crown of a tooth is defined as dilaceration. , Dilaceration is of great importance to orthodontics because dilacerated roots are harder to move orthodontically, have a higher risk of impaction or external resorption, and impede favorable insertion of miniscrews. Orthodontic management of dilacerated roots is complex and lengthy and requires indefinite maintenance. The prevalences of root dilaceration have been generally investigated in several ethnic groups, which ranges from 0.3% to 17% without gender predilection. ,
To date, several potential etiologic factors for root dilaceration have been proposed. When dilaceration occurs in permanent incisors, it is often supposed as a result of trauma to the primary predecessors whose apices lie close to the permanent tooth germ. An intrusion injury places the apex of the primary tooth in close approximation to the tooth bud of permanent successors, increasing the likelihood of damage to the tooth bud and the Hertwig epithelial root sheath. However, it has been found that the prevalence of dilacerated permanent successor teeth is generally disproportionate to the incidence of injuries in the corresponding deciduous teeth. This implicates that trauma may not be the major etiologic factor of dilaceration because most dilacerated teeth are found in the posterior area, which is less likely to have a history of trauma. Other probable etiologic factors include insufficient space for development, the effect of anatomic structures (such as the cortical bone of the maxillary sinus or the nasal fossa), supernumerary tooth, mechanical interference with an eruption in cases such as an ankylosed or retentive primary tooth, and hereditary factors. ,
Previously, a relationship between maxillary canine impaction and root dilaceration has been proposed. Hettiarachchi et al reported that palatally impacted maxillary canines have a greater tendency to develop apical hooks. He also concluded that PICs have shorter root length than nonimpacted maxillary canines. However, this study covered only PIC in Caucasians. It is well-known that BIC and PIC are different from various standpoints such as ethnical prevalence and etiologic factors. , Briefly, buccally impacted canines (BICs) are mostly linked to dental arch and skeletal size deficiencies, whereas PICs are theorized to be associated with genetic origins or lack of guidance from the adjacent lateral incisors. Moreover, previous studies concentrating on root dilaceration of impacted canines in Asian populations are scarce. Hence, the association of root dilaceration and impacted canines and whether the prevalence of root dilaceration differs between the 2 impaction types in Asians have yet to be determined.
Numerous studies on patients with normally erupted maxillary canine reported that maxillary premolars and lateral incisors are relatively more frequently dilacerated. , , In addition, few case reports on the concurrent incidence of maxillary canine impaction and adjacent premolar root dilaceration suggested a relationship between them. Therefore, to clarify this issue, a large sample study is necessary to investigate the prevalence pattern of root dilaceration in adjacent teeth of maxillary impacted canines. The purpose of this study was to investigate the association between root dilaceration and BICs or PICs as well as their adjacent teeth in population with the cone-beam computed tomography (CBCT) technique. The null hypothesis was that either the maxillary impacted canines or their adjacent teeth would not present a difference in their dilaceration prevalence.
Material and methods
Pretreatment CBCT images of 145 Chinese subjects with unilateral maxillary canine impaction (experimental group) and 145 age- and sex-matched subjects without impaction (control group) were obtained from the Affiliated Hospital of Stomatology, Nanjing Medical University (Nanjing, China) ( Table I ). The inclusion criteria for the experimental group were clinically and radiographically diagnosed patients of unilateral maxillary canine impaction. The experimental group was subclassified as BICs and PICs. The exclusion criteria were patients having canines with open apices, missing or root resorption of adjacent lateral incisors and first premolars, history of systemic disorders, and undergoing orthodontic treatment. All subjects in the control group were patients with normally erupted canines who met the same exclusion criteria and prescribed CBCT for another diagnostic reason. Before the imaging process, all patients signed the consent form that their radiological results (demanding no personal identification disclosure) could be used for future research on maxillary canine impaction. Ethics approval was granted by the Ethical Committee Department of Affiliated Hospital of Stomatology, Nanjing Medical University (PJ2018-031-001). The present study was carried out after approval from the International Clinical Trial Registry (Protocol no. ChiCTR1800020036).
| Characteristics | Experimental group | Control group, n = 145 | P value | |
|---|---|---|---|---|
| Buccal (n = 74) | Palatal (n = 71) | |||
| Sex | ||||
| Female | 49 (66.2) | 39 (54.9) | 88 (60.7) | 0.394 ∗ |
| Male | 25 (33.8) | 32 (45.1) | 57 (39.3) | |
| Age, y | 17.08 ± 4.88 | 18.62 ± 5.18 | 17.73 ± 5.04 | 0.183 † |
| Angle classifications | ||||
| Class I | 33 (44.6) | 30 (42.3) | 70 (48.3) | 0.705 ∗ |
| Class II | 28 (37.8) | 23 (32.4) | 48 (33.1) | |
| Class III | 13 (17.6) | 18 (25.3) | 27 (18.6) | |
∗ Comparison with chi-square tests among the 3 groups.
† Comparison with 1-way analysis of variance tests among the 3 groups.
All CBCT data were acquired from the patients with a standard acquisition protocol using the same CBCT machine (NewTom VG; QR, Verona, Italy) and the same parameters: 16-cm diameter field of view, 110 kV, 1-20 mA (pulsed mode), and 0.3-mm voxel size. After removing patient identification information from the CBCT data (digital imaging and communications in medicine files), they were entitled to randomly generated codes and subsequently analyzed by a rater on the basis of the following standardized protocol. Digital imaging and communications in medicine files were first imported into SimPlant O&O (version 13.0; Materialise NV, Leuven, Belgium) and segmented to display the teeth and skull for 3-dimensional surface rendering at the threshold value of teeth (1250-3070) and skull (250-3070) in the software. The images were reoriented according to a protocol described by Molen. Afterwards, qualitative and quantitative variables ( Table II ) were assessed and confirmed in the volumetric and 3 orthogonal (sagittal, coronal, and axial) 2-dimensional views. In both study groups, maxillary impacted canines and their adjacent teeth were classified as no dilaceration, with a root curvature, and with an apical hook according to the angular degree of root dilaceration ( Fig ). The landmarks for measuring quantitative variables ( Table II ) were identified in the volumetric view using the digitizing landmarks tool of the software. After verifying the sagittal, coronal, and axial views, these landmarks were used to measure quantitative image variables using a digital linear measurement tool (to 0.01 mm precision) in the software. Before the measurement process, each to-be-evaluated tooth in the control group was selected according to its own maxillary left or right coinciding canine or adjacent tooth present in the matched subject from the experimental group.
| Measurements | Definition |
|---|---|
| Qualitative variables | |
| Root curvature | Presence of flexion of the apical third of the root between 10° and 50° from the long axis of the tooth (a line joining the cusp tip and the midpoint of the root) |
| Apical hook | Presence of angulation in the apical third of the root 50° or more to the long axis of the root ( Fig ) |
| Quantitative variables | |
| Crown length | Distance between the cusp tip and the midpoint of the labial cementoenamel junction |
| Root length | Distance between the labial cementoenamel junction and the root apex |
| Angulation of the canine to the midsagittal plane | The acute angle between the long axis of the impacted canine and the midsagittal plane |
To assess intraexaminer reliability, we repeated measurements of 100 randomly selected subjects from the whole sample by the same rater (B.S.) after a 1-month interval. With assumptions of 30% and 10% prevalence rates of curvature in our impacted and control samples, respectively, a minimum sample size of 56 was required to achieve 80% power (calculated in G∗Power [version 3; Heinrich Heine University, Düsseldorf, Germany]) to detect differences of root curvature prevalence and even less than that for the hook. Our samples with buccal (n = 74), palatal (n = 71), and combined (n = 145) impactions had power values of 96.5%, 96.0%, and 99.5%, respectively.
Statistical analysis
Cohen weighted kappa (for qualitative variables) and intraclass correlation tests (for quantitative variables) were used to assess intrarater reliability. The prevalence of dilaceration in canines and adjacent teeth were comparatively analyzed between the experimental and control groups and between the BICs and PICs subgroups by chi-square tests or Fisher exact tests (if required). McNemar test was used to compare the prevalence of dilaceration between impacted and erupted contralateral canines in the experimental group. Chi-square test also helped us to evaluate the prevalence of root curvature and apical hook in canines. One-way analysis of variance was used to compare mean crown and root length measurements among the 2 canine impaction subgroups and the control group. The angular positioning of all the impacted canines was also analyzed by 1-way analysis of variance. In case of any found significance, the least significant difference post-hoc test was used. All statistical analyses were performed using SPSS (version 24.0; IBM, Chicago, Ill), and P < 0.05 was considered statistically significant.
Results
Characteristics of sex, age, Angle classifications, and canine eruption site of the subjects are shown in Table I . Among all the unilateral maxillary canine impaction subjects, 74 were buccally positioned, and 71 were palatally positioned. In general, intrarater reliability for image assessment was excellent for both qualitative (Cohen weighted kappa tests, κ > 0.9) and quantitative variables (intraclass correlations, r > 0.9).
As shown in Table III , the prevalence of root dilaceration in maxillary impacted canines of the experimental group was significantly higher than the coinciding erupted canines in the control group ( P < 0.001). Significant differences in root dilaceration prevalence were also found in adjacent lateral incisors ( P < 0.001) and premolars ( P = 0.001) of the experimental group, compared with those of the control group ( Table III ).
