|Year : 2015 | Volume
| Issue : 1 | Page : 19-24
Dento-skeletal characteristics of subjects with impacted mandibular canine(s)
Shikha Jain1, AT Prakash2, Mamta Agrawal3
1 Reader, Department of Orthodontics, PDM Dental College and Research Institute, Bahadurgarh, Haryana, India
2 Professor, Department of Orthodontics, Bapuji Dental College and Hospital, Davangere, Karnataka, India
3 Reader, Department of Oral and Maxillofacial Surgery, Purvanchal Institute of Dental Sciences, Gorakhpur, Uttar Pradesh, India
|Date of Submission||30-Aug-2014|
|Date of Acceptance||24-Mar-2015|
|Date of Web Publication||12-Jun-2015|
Department of Orthodontics, PDM Dental College and Research Institute, Bahadurgarh, Haryana - 124 507
Source of Support: None, Conflict of Interest: None
Objectives: A cross-sectional clinical study was designed to analyze selected dento-skeletal characteristics of the patients with impacted permanent mandibular canine (s) (PMC[s]). Materials and Methods: Pretreatment lateral cephalograms of 39 subjects diagnosed with mandibular canine (s) impaction (impaction group, "IG") and 78 subjects of the control reference sample (control group, "CG") were used to analyze selected dento-skeletal characteristics. Comparisons were made between the groups using independent 't'-tests and Chi-square tests. Odds of specific diagnostic sub-categories between "IG" and "CG" were evaluated in terms of odds ratios. Statistical significance was set at P < 0.05. Results: Both the statistical tests gave similar results. The odds ratio of 8.99 (P < 0.0001) and 3.05 (P = 0.005) at 95% confidence interval indicated significantly strong connection of mandibular canine impaction with skeletal Class II and retroclined maxillary incisors, respectively. Conclusions: When compared with controls, cases exhibiting PMC (s) impaction revealed a trend toward retrognathic mandible, skeletal Class II, retroclined incisors.
Keywords: Dento-skeletal, eruption, genetic, impacted
|How to cite this article:|
Jain S, Prakash A T, Agrawal M. Dento-skeletal characteristics of subjects with impacted mandibular canine(s). J Indian Orthod Soc 2015;49:19-24
|How to cite this URL:|
Jain S, Prakash A T, Agrawal M. Dento-skeletal characteristics of subjects with impacted mandibular canine(s). J Indian Orthod Soc [serial online] 2015 [cited 2019 Jun 16];49:19-24. Available from: http://www.jios.in/text.asp?2015/49/1/19/158629
| Introduction|| |
As early as 1951, Bluestone first described impacted permanent mandibular canine (s) (PMC[s]).  It has been suggested that the eruption disturbance of the mandibular canine is most often caused by anomaly of the canine germ itself, and in rare cases by space deficiency or pathological obstacles like supernumerary teeth, over-retained deciduous canine and cysts or tumors.  Excessive spacing apical to the root apices of the mandibular incisors has been implicated for not providing adequate guidance to the canines to erupt into their position.  Despite numerous etiopathogenetic mechanisms, the specific cause remains unknown. 
Impacted mandibular canines are often discovered without having produced any apparent symptoms suggestive of their presence.  It is possible that routine full-mouth intraoral dental radiographs may fail to reveal impacted canines.  However, an increase in the number of patients with this phenomenon has recently been noted due to the widespread availability of dental pantomographs. , Failure of the eruption of a structurally and functionally important tooth like PMC may lead to the collapse of the mandibular arch with attendant implications for the overall orthodontic treatment of these patients. As for any other tooth in the dental arch, complications secondary to impaction of mandibular canine are well-known.  Strikingly, PMC is also one of the most frequently found tooth to be associated with transmigration.  While most transmigrating canines are asymptomatic, follicular cystic formation and chronic infection with fistulae have been reported.  Hence, accurate and early diagnosis of ectopic eruption/impaction is the need of an hour. Joshi  emphasized that for interception, it is best to detect patient's presenting characteristics that are most related to this eruption anomaly when they are between 8 and 9 years old. It is likely that early observation of possible dento-skeletal characteristics that may be associated with PMC impaction may indicate an increased risk for the later appearance of this anomaly. Indeed, recent case reports on co-existence of deep bite, Class II or Class III skeletal patterns and increased lower facial height with mandibular canine eruption disturbances lend sufficient credence to the possibility of predicting impacted mandibular canines based on the specific dento-skeletal morphological parameters. 
Hence, we sought to measure and analyze selected dento-skeletal characteristics on the lateral cephalograms of the patients with impacted mandibular canine (s). Besides contributing to the dental literature on a rare,  but orthodontically important anomaly, the results are likely to yield clinically useful information pertaining to the risk factors, early diagnosis and eventual treatment planning of mandibular canine impaction.
| Materials and Methods|| |
Following the approval of institutional review board, a cross-sectional clinical study was designed and undertaken at Department of Orthodontics, Purvanchal Institute of Dental Sciences (PIDS), Gorakhpur, India. This research was conducted in full accordance with ethical principles, including those from "Declaration of Helsinki."
A multistage sampling technique was adopted to select the subjects with PMC (s) impaction from various schools of the district Gorakhpur, Uttar Pradesh, India. The geographic map of the district was procured and was divided into 12 zones, based on Gorakhpur Municipal Corporation. Two schools were selected from the list of all the high schools of each zone and all their students who were at least 16 years of age were evaluated. Initially, a total of 7223 (females: males, 0.9:1) subjects were screened. Forty-four subjects fulfilled the selection criteria for the diagnosis of PMC (s) impaction, as based on the subject's history, clinical and radiographic examination (Orthopantomograph, Occlusal, Intra Oral Periapical views with Clark's rule and Lateral cephalogram in occlusion).  Mandibular canine was accepted as impacted:
Factors like clinical or radiographic evidence of supernumerary teeth, odontoma or cyst directly related to the unerupted mandibular canine (s); congenitally missing teeth including mandibular canine (s) (but excluding third molars); history of trauma or extraction of any primary or permanent tooth, presence of gross caries interproximally, orofacial clefts or any other hereditary, syndromic or systemic manifestations and previous endodontic treatment of primary mandibular canines that possibly influenced eruption of PMC; dissimilar dental  and skeletal  (Class I, II and III) classification categories; history of prior orthodontic intervention and inadequate diagnostic records led to the exclusion of 5 subjects.
- If it was identified to be prevented from erupting either by a physical barrier or because of its orientation in a position other than vertical within the periodontal structure 
- If it showed radiographic evidence of complete root formation 
"Impaction group" ("IG"): Finally, 39 subjects were considered for inclusion in "IG." All the subjects were Indian by origin and ranged from 16 to 19 years of age with the 17.2 ± 1.5 years.
"Control group" ("CG"): Control reference sample consisted of seventy-eight age- and sex-matched Indian subjects who formed the part of the orthodontic patient pool at PIDS, Gorakhpur. These subjects had complete eruption of both the PMCs, as evident from their pretreatment models retrieved from the departmental archives.
Lateral cephalometric radiographs were hand traced for each subject with a 0.5 mm pencil on matte acetate tracing paper. All cephalometric measurements were performed by the same investigator (SJ). Following characteristics were measured and assessed: SNB angle, ANB angle, ML/SN angle, SpL/ML angle, LI/ML angle, UI/SN angle and general vertical facial configuration.
The sagittal position of the mandible to the skull base (SNB angle) was defined according as orthognathic (SNB = 76-80°), prognathic (SNB >80°) and retrognathic (SNB <76°).  The sagittal skeletal relationship between the maxilla and mandible (ANB angle) and vertical skeletal relationship between the mandible and cranial base (ML/SN angle) was defined as: Skeletal Class I (ANB = 0-4°), skeletal Class II (ANB >40°) or skeletal Class III (ANB < 0°)  and normodivergent (ML/SN angle = 27-37°), hypodivergent (decreased vertical face height, ML/SN angle < 27°) or hyperdivergent (increased vertical face height, ML/SN angle >37°) respectively.  The SpL/ML angle describes the inclination of the mandible (ML) in relation to the maxillary base (SpL, bispinal line or palatal line). It is used for the evaluation of the maxillary-mandibular skeletal relationship in the vertical plane and its normal value ranges from 23° to 33°.  Inclination of the mandibular central incisors in the sagittal plane (measured as the angle between the longitudinal axis of the most prominent mandibular central incisor and mandibular plane, LI/ML angle) was defined as standard inclination (LI/ML angle = 86-93°), proclination (LI/ML angle > 93°) and retroinclination (LI/ML angle < 86°).  Inclination of the maxillary central incisors in the sagittal plane (measured as the angle between the longitudinal axis of the most prominent maxillary central incisor and anterior cranial base, UI/SN angle) was defined as average inclination (UI/SN angle = 100-104°), proclination (UI/SN angle > 104°), and retroinclination of the maxillary central incisors (UI/SN angle <100°).  General vertical facial configuration as assessed using sum angle (sum of saddle, articular, and gonial angles) and Jarabak's ratio indicated the tendency for posterior/clockwise or anterior/counter-clockwise rotation of the mandible, thus indicating vertical or horizontal growth pattern, respectively. Sum angle = 396° ±6° indicates average growth pattern, while < 390° and > 402° indicated horizontal and vertical growth direction, respectively. The mean value for Jarabak's ratio is 62-65%. 
All the measured variables were described in terms of means and standard deviation. As normal distributions for the angles SNB, ANB, ML/SN, and SpL/ML, LI/ML, UI/SN, sum angle and Jarabak's ratio were found, independent 't'- tests were employed to test the differences between the two groups viz "IG" and "CG." The selected characteristics were then split into respective diagnostic sub-categories (as given above). The differences in the relative distribution of the various diagnostic sub-categories between the two groups were tested by Chi-square tests (or Fisher's exact tests when a number of subjects in any group were <5). Level of significance of all tests was set at P < 0.05. Statistical analyses were performed using SPSS (version 17, Chicago, Illinois, USA).
Duplicate measurements were undertaken 2 weeks later by the same examiner using 20 lateral cephalograms, randomly selected from each group. Intra-examiner reliability for was assessed using double determination method.
| Results|| |
The distribution of subjects with PMC (s) impaction as stratified by location and gender is summarized in [Table 1]. Of 39 subjects in "IG," only 5 (12.82%) were affected bilaterally. In the remainder cases, impaction occurred with almost similar frequency on the right (48.72%) and left sides (38.46%). Female: Male ratio was 2.25:1.
|Table 1: Distribution of PMC[s] Impaction cases according to location and gender |
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All cephalometric measurements showed statistically insignificant measurement error.
Statistical comparison between the "IG" and "CG" showed significant differences with respect to four measurements viz. SNB angle, ANB angle, LI/ML angle and UI/SN angle [Table 2]. As shown in [Table 3], "IG" is characterized by statistically significant more frequent occurrence of retrognathic mandible (P = 0.033, Chi-square = 6.821), skeletal Class II (P = 0.000, Chi-square = 27.771), retroclined mandibular incisors (P = 0.000, Chi-square = 21.336) and retroclined maxillary incisors (P = 0.000, Chi-square = 22.220). Odds ratios were used for the evaluation of SNB angle, ANB angle, LI/ML and UI/SN angle as the prospective risk factors for IG/CG [Table 4]. Among all the odds ratios above unity which indicated the risk a particular diagnostic sub-category carries for the occurrence of impacted mandibular canines, only the ones for skeletal Class II and retroclined maxillary incisors were found to be statistically significant (8.99, P < 0.0001; 3.05, P = 0.005, respectively).
|Table 2: Comparison of mean values of the measured characteristics between the studied groups using independent 't' test |
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|Table 3: Distribution of dento - skeletal characteristics and statistical evaluation of differences in frequencies of various diagnostic sub - categories between the 'IG' and 'CG' |
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|Table 4: Ratio of odds of various diagnostic sub - categories between 'IG' and 'CG' |
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| Discussion|| |
We found the prevalence of PMC impaction to be 0.61% in the present study. The difference from the previous reports ,,, is likely attributed to the racial factors, study design and sampling techniques. Female predilection observed in the present study was strikingly more obvious than the previous reports.  Observations on the location of impaction (right vs. left and unilateral vs. bilateral), however, closely paralleled previous studies. 
As far as the number of subjects in "IG" is concerned, it reflects the probable representation of mandibular canine (s) impaction in the subpopulation studied. Even though this number may be small to allow meaningful interpretation of the data, a sample size of thirty-nine appears to be reasonable for a study investigating a relatively unusual anomaly of mandibular canine impaction and for one that is the first to report its frequency in Indians. Furthermore, as it was considered unethical to subject the subjects initially screened but who had complete eruption of both the PMC/s to radiographic examination, use of the orthodontic pool was justified to formulate the control group. Keeping in mind that the growth of the mandible continues at a relatively steady rate before puberty, unlike thereafter; we selected patients only above 16 years of age for this study. 
There is no dearth of case reports on eruption disturbances of PMC. Recently, Holla et al.  identified morphologic parameters associated with seven cases of unilateral transmigrating canines. Six cases had Class II malocclusion, with five cases having a deep bite (>40%) and a deep curve of Spee. Five cases showed increased lower anterior facial height. The authors correlated these parameters with greater space availability on the apical level of mandibular incisors and the loss of role of lateral incisor root as a navigator of the canine crown during its eruption, thereby supporting the guidance theory. This view is substantiated by Vichi and Franchi L  who contended that proclination of the lower incisors, increased axial inclination of the unerupted canine and an enlarged symphyseal cross-sectional area of the chin could play an important role in the mechanism of transmigration. Yet, Joshi  disagreed with the idea of lower incisor proclination and enlargement of the symphysis as etiologic factors. He believes that this is a consequence of canine migration, not a cause. Hence, both the dentoskeletal characteristics as well as the etiological factors related to PMC impaction stand unclear. In fact, to our knowledge, this is one of the first research to attempt to identify selected dento-skeletal characteristics in patients with impacted mandibular canine (s), using lateral cephalograms.
Four cephalometric characteristics viz. SNB angle, ANB angle and LI/ML and UI/SN angle showed statistically significant differences between the two groups. This indicated the tendency of PMC impaction cases to be associated with the retrognathic mandible, skeletal Class II, retroclined mandibular and maxillary incisors, when compared to the controls. The results of independent 't'- test were supported by those of Chi-square tests. The latter showed that unlike orthognathic and prognathic positions, the retrognathic position of the mandible occurred significantly more frequently in "IG." In contrast to 40.70% of those without impaction, a greater bulk of subjects (86.05%) with mandibular canine (s) impaction were found to be associated with skeletal Class II. In fact, the odds ratio of 8.99 at 95% confidence interval indicated significantly strong connection of mandibular canine impaction with skeletal Class II (P < 0.0001). This is in accordance with the observation made by Holla et al.  that approximately 85% of cases with eruption disturbances of mandibular canines had skeletal Class II. We also found that retroclined mandibular and maxillary incisors occurred significantly most frequently and proclined mandibular incisors significantly least frequently in "IG." The odds ratio of 3.05 at 95% confidence interval indicated the significant association of mandibular canine impaction with retroclined maxillary incisors too (P = 0.005). As Class II division 2 malocclusion (Class II/2) is typically associated with retroclined incisors, , the results of the present study, in this context, are complementary to those of our previous study wherein we considered Class II/2 as a possible risk factor for mandibular canine (s) impaction.  Strikingly, Class II/2 was proposed as a risk factor for palatal impaction of maxillary permanent canine too.  Decreased occurrence rate of proclined mandibular incisors in "IG," however, is contrary to the observations made in the most case reports , that suggested lower anterior proclination as a factor contributing to eruption disturbances of PMC. This is likely due to the fact that most of these reports focused on transmigrated impacted canines alone, whereas we analyzed PMC impaction in a broader perspective irrespective of the presence or absence of transmigration. After all, proclined mandibular incisors are only assumed to favor transmigration , and not all impacted canines transmigrate. 
Peck cited the role of genetics in the etiology of eruption disturbances PMC.  As far as the facial morphology of the individual is concerned, it is established early in one's life and is also known to be influenced by heredity. , Moreover, Class II/2 craniofacial type is closely related to numerous gene controlled dental anomalies.  From these perspectives and in collaboration with the understanding of the results of the present study, it seems reasonable to assume that skeletal Class II may be biologically or genetically related to mandibular canine (s) impaction. This is validated by the growing body of evidence that identifies a complex of genetically controlled dental disturbances that often occur in combination, such as concurrent occurrence of double transmigration and hyperdontia. ,, The point of clinical significance is that skeletal Class II and retroclined maxillary incisors could serve as "microsymptoms" of PMC impaction. This shall be true especially when it occurs in combination with the other associated dento-skeletal characteristics like retrognathic mandible along with retroclined mandibular incisors, as found in the present study; and dental anomalies like retained primary canines, tooth-size alterations and ectopic eruption of maxillary canines etc. ,, Certainly, this information may help in early identification of the candidates who would likely benefit from interceptive treatment.
The above findings must be considered preliminary and further verification in a more extensive study with more elaborate resources is recommended. It shall be of great interest in view of the present clinical results (association of mandibular canine impaction with selected dento-skeletal characteristics) to examine whether genes associated with mandibular canine eruption/impaction are also involved in controlling dento-skeletal features.
| Conclusion|| |
When compared with controls, subjects exhibiting PMC (s) impaction revealed a trend towards retrognathic mandible, skeletal Class II and retroclined mandibular and maxillary incisors. In addition, a strong connection of skeletal Class II relationship and retroclined maxillary incisors was observed in subjects with mandibular canine (s) impaction.
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[Table 1], [Table 2], [Table 3], [Table 4]