Year : 2009 | Volume
: 20 | Issue : 3 | Page : 340--345
Localization of impacted permanent maxillary canine using single panoramic radiograph
S Sudhakar, Karthikeya Patil, VG Mahima
Departments of Oral Medicine and Radiology, J.S.S. Dental College and Hospital, Mysore - 570 015, Karnataka, India
Departments of Oral Medicine and Radiology, J.S.S. Dental College and Hospital, Mysore - 570 015, Karnataka
Background and Objectives : The objective in localization is selection of a suitable technique which has minimal radiation dose, cost and maximum details. Panoramic radiograph, being a screening radiograph, can satisfy the above needs. Taking this into consideration, the present study was done to evaluate the reliability of panoramic radiograph in localization of impacted permanent maxillary canines by applying the criteria suggested by Chaushu et al. and by comparing it with Clark«SQ»s rule.
Materials and Methods : The study comprised of 114 subjects in the age group of 13-30 years of both the genders with 150 impacted canines visiting Department of Oral Medicine and Radiology during the study period. The study subjects were examined for clinically missing canine, and then confirmed with intra-oral peri-apical radiograph (IOPAR). Panoramic radiographs (for application of Chaushu et al. criteria) and IOPAR«SQ»s (for application of Clark«SQ»s rule) of the subjects were made and interpreted for parameters pertaining to the impacted canines. The data obtained was tabulated and subjected to statistical analysis using the statistical package for social sciences (SPSS) software.
Results : Determination of the bucco-palatal position from panoramic radiographs, by applying Chaushu, et al. criteria, showed that localization in bucco-palatal position was possible for 96 of the 102 impacted canines placed in the middle and coronal zones. The remaining six impacted canines, three each in the middle and coronal zones, could not be localized as they showed overlapping in their range. By excluding them, the overall agreement worked out to be 94.11%. Localization was not possible for 48 impacted canines that lied in the apical zone.
Conclusion : A single panoramic radiograph can serve as a reliable indicator for determining the bucco-palatal position of the impacted canines when they lie in the middle and coronal zones. When they lie in the apical zone it is recommended to explore their presence with other conventional or advanced imaging modalities.
|How to cite this article:|
Sudhakar S, Patil K, Mahima V G. Localization of impacted permanent maxillary canine using single panoramic radiograph.Indian J Dent Res 2009;20:340-345
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Sudhakar S, Patil K, Mahima V G. Localization of impacted permanent maxillary canine using single panoramic radiograph. Indian J Dent Res [serial online] 2009 [cited 2019 Oct 21 ];20:340-345
Available from: http://www.ijdr.in/text.asp?2009/20/3/340/57381
Over the years various radiographic techniques have been applied, to locate the impacted permanent maxillary canines, with varied outcome. Very few studies had considered the usage of single panoramic radiograph for the purpose. It would be advantageous to use panoramic radiographs in localizing impacted maxillary canines as it is the most commonly recommended screening radiograph, delivers relatively less radiation, easy to perform, cost-effective and readily available. ,,
This study was designed to evaluate the reliability of panoramic radiograph in localization of impacted permanent maxillary canine by applying the criteria suggested by Chaushu, et al.  and by comparing it with Clark's rule. 
The criteria for localization of impacted maxillary canine as suggested by Chaushu, et al.  include the vertical restriction parameter and magnification index. According to the vertical restriction parameter, the position of the crown of the impacted canine in relation to the root surface of the adjacent erupted central incisor can be either at the apical, middle or at coronal root third level on the panoramic radiograph. The authors state that impacted canines found in the coronal zone are most likely to be buccally located whereas those in the middle zone have a strong likelihood of palatal placement. The canines located in the apical zone can be either buccally or palatally located.
To apply magnification index, the widest mesio-distal dimension of the impacted canines to that of the ipsilateral erupted central incisor and contra lateral erupted canine are measured and their values are recorded as Canine Incisor Index (CII) and Canine-Canine Index (CCI) respectively. Chaushu, et al.  established a cut-off point of 1.15, as they found that regardless of the vertical position on the panoramic radiograph all the buccally located canines had a value less than 1.15 whereas the value of palatally located canines was more than 1.15.
Materials and Methods
The study subjects were selected from outpatients visiting Department of Oral Medicine and Radiology during the study period. The study group included 114 patients in the age group of 13-30 years of both the genders. Only patients with clinically missing and impacted corresponding maxillary permanent canines, either unilateral or bilateral and with completely erupted ipsilateral central incisors were included in the study. The final study sample accounted to 114 patients with 150 impacted canines.
A written informed consent was obtained from all the study subjects, A copy of it was submitted to the institutional ethics review board and approval was obtained.
A single panoramic radiograph (conventional panoramic machine- Rotograph Eur-243, Villa, Italy with a magnification factor of 1.5) for application of Chaushu, et al.  criteria and two IOPAR's for each impacted canine using bisecting angle technique for Clark's rule  were made on each study subject.
Panoramic radiographs showing impacted canines whose placement would not be possible to locate using the parameters employed in the study were planned, for exclusion, but none of the selected cases showed such placement. However, panoramic radiographs showing more than five per cent unequal magnification were repeated. To ensure equal horizontal magnification, the widest mesio-distal dimension of the mandibular first molars on both sides were measured and compared. Mandibular second molar was considered for the above measurement in cases where first mandibular molar was missing. All the radiographic interpretations were performed by the third investigator, an oral radiologist.
The position of the impacted canines from the IOPAR's was determined as follows by applying Clark's rule.  The position of the crown of the impacted maxillary canine from the first IOPAR, taken with ideal angulation, was noted in relation with the crown or the root of the adjacent tooth or its pulpal canal. This was then compared with the second radiograph taken with a distal angulation. The impacted canine was interpreted as lingually placed when it appeared to have moved in the same direction as the shift of the tube head (distal) on the second radiograph. Conversely, it was interpreted as buccally placed when the impacted canine seen on the second radiograph appeared to have moved in the direction opposite to the shift of the tube head (mesial). 
Later, a corresponding panoramic radiograph was taken for determination of the labio-palatal position of impacted maxillary canine by applying the magnification index and vertical restriction criteria as suggested by Chaushu, et al. 
The following measurements were then recorded from the panoramic radiographs.
The widest mesio-distal (MD) dimension of the impacted canine measured on a line perpendicular to its long axis.The widest mesio-distal dimension of the ipsilateral central incisor measured on a line perpendicular to its long axis.In each case, when the contra lateral canine is in correct position (unilateral canine impaction cases), its widest mesio-distal dimension were also measured.Canine Incisor Index [CII] was calculated using the formula[INLINE:1]In cases with unilaterally impacted canine, Canine Canine Index [CCI] was calculated using the formula.[INLINE:2]The measurements determined were recorded as the magnification index.Vertical restriction criteria
The root length of the ipsilateral central incisor was measured and divided into three equal zones perpendicular to its vertical axis by marking two horizontal lines with a marker pen as mentioned below [Figure 1].
The apical zone - the apical third of the rootThe middle zone - the middle third of the rootThe coronal zone - the remainder of the root
The position of the crown of the impacted canine in relation to these zones was determined as its vertical position.
The positions of the impacted maxillary canines on the panoramic radiographs were determined in the following manner:
The IOPAR's of buccally and palatally placed canines and its corresponding panoramic radiographs were divided into two different groups.To apply the vertical restriction criteria as suggested by Chaushu, et al.  the panoramic radiograph of both the groups were further sub-divided based on the three different zones as stated earlier.To apply the magnification criteria, the CII and CCI values were measured from all the panoramic radiographs.When the CII and CCI values were less than 1.15, the impacted canines was considered to be buccally placed and when more than 1.15, they were considered as palatally placed, based on the cut of point as suggested by Chaushu S, et al.  This was based on the fact that for a given focal spot-film distance, objects placed palatal to the image layer appears excessively magnified in the horizontal plane, while buccally located objects appear proportionally diminished.
The bucco-palatal positions of the impacted canines as determined by the criteria put forth by Chaushu, et al.  and by Clark's rule  which was considered as standard were compared and their reliability estimated.
A similar procedure was adopted for interpretation of all the radiographs. All the above mentioned measurements and interpretations were repeated after a period of two weeks by the same investigator and the mean was used in cases where discrepancies were found.
The data obtained were tabulated and subjected to statistical analysis. The following statistical methods were adopted utilizing the statistical package for social sciences (SPSS) software:
The distribution of bucco-lingual position of canines determined by IOPAR to that of panoramic radiographs were evaluated.The range, mean and standard deviation of CII and CCI ratio were estimated with their P values.The 'P' values were derived by adopting the independent t-test.The significance was provided at P less than 0.05 or P less than 0.01.
Based on the Clark's rule, of the 150 impacted permanent maxillary canines, 84 (56%) were buccally placed and 66 (44%) were palatally placed.
Based on the vertical position on the panoramic radiographs, of the 150 impacted permanent maxillary canines, 48 (32%) were positioned in the apical zone, 59 (39.3%) in the middle zone and 43 (28.7%) in the coronal zone. When the 84 (56%) buccally impacted canines were categorized in the vertical position, 36 (42.9%) were located in the apical zone, 20 (23.8%) in the middle zone and 28 (33.3%) in the coronal zone. Twelve (18.2%) canines were located in the apical zone, 39 (59.1%) in the middle zone and 15 (22.7%) in the coronal zone when the 66 (44%) palatally impacted canines were categorized in the vertical position [Table 1].
Based on the magnification index, for 84 (56%) of the 150 impacted permanent maxillary canines, the CII values ranged from 0.78-1.42. For the 66 (44%) palatally impacted canines, the CII value ranged from 0.75-1.60. There were 77 (51%) unilaterally impacted permanent maxillary canines of which 42 (54%) were buccally impacted and their CCI values ranged from 1.00-1.66. For the 35 (46%) palatally impacted canines it ranged from 1.00-1.60 [Table 2] and [Table 3].
Determination of the bucco-palatal position from panoramic radiograph by applying vertical restriction and magnification index (with the cut-off point 1.15) depicted that localization in bucco-palatal position was possible in 96 out of 102 cases placed in the middle and coronal zones. Localization was not possible for six canines (three in the middle zone and three in the coronal zone) as they showed overlapping in their CII and CCI range. By excluding them, the overall agreement for the 102 impacted canines worked out to be 94.11%. The remaining 48 canines that lied in the apical zone were not amenable to bucco-palatal localization as they showed overlapping in their CII and CCI ranges [Table 2],[Table 3] and [Figure 2].
Permanent maxillary canines are the third most common tooth to be impacted next to mandibular and maxillary third molars. , Position of canine is of clinical significance since it is regarded as the corner stone of the dental arch and its role in occlusion during mandibular lateral excursion is equally well known. ,
Treatment options for the impacted canine include observation, extraction, auto transplantation and orthodontic pulling. Early localization of the impacted maxillary canine is important as interceptive treatment, such that extraction of the deciduous predecessor can allow spontaneous correction in many cases. Such treatment decisions are aided by determination of its position in three dimensional planes. This is aided by combination of clinical and radiographic findings. 
Impacted permanent maxillary canines are most commonly seen on the palatal side. Reports suggest that the percentage of palatal placement ranges from 40%-75% ,,, and it varies depending on the number of cases and technique of localization applied. In the present study 44% of the canines were palatally placed, this is in accordance with Marzouk et al. 
Clinical evaluation of the exact location of the impacted canine is often difficult. The clinician should therefore rely entirely on the radiographic evidence alone.  Several radiographic techniques for determining the position of the unerupted maxillary canines have been advocated in the past either in single or in combinations, with every effort taken towards minimizing the radiation dose and cost while maximizing the information.
In 1909, Clark  introduced the horizontal tube shift technique using two IOPARs and later on in 1952 Richards  introduced the concept of vertical tube shift. The above method is also called 'parallax method' and is the radiographic technique of choice of many diagnosticians till date. Over the years, various radiographic combinations were utilized to localize the impacted canines by parallax method namely combination of occlusal and peri-apical radiographs, redundant images from panorex units, combination of occlusal radiographs, combination of panoramic and occlusal radiographs using vertical or horizontal tube shift. ,,,
The parallax method had a disadvantage of not orienting the impacted tooth in three dimensions. Hence, combinations of radiographs taken right angle to each other were used and this technique was called as 'right angle technique'. The combination of radiographs, taken at right angles to each other, included peri-apical, occlusal, orthopantomograph, lateral and postero anterior cephalometric radiographs. ,
The concept of using single radiograph in localizing impacted canines began in 1934 when Bosworth , introduced multiple exposures in a single peri-apical radiograph and interpreted them by applying parallax method. The disadvantages include multiple exposures and overlapping of structures. For a while vertex occlusal radiograph was used applying the millimeter rule.  According to this rule, a line is drawn along the midpoint of the arch and another two lines of 1mm each are drawn anterior and posterior to it. If an impacted canine is found within these three lines they are said to be lying within the arch and if they are found lying outside these lines they are interpreted as buccally or palatally placed. However, the radiation exposure and superimposition of other anatomical structures with this method proved disadvantageous. 
Later on, panoramic radiograph was considered for localization of impacted canines for a period of time. Regardless of the method applied the conventional radiographs does not show the exact appearance of the impacted tooth in its longitudinal axis and the relationship with the neighboring bony structures.  Of late computerized tomography (CT) and cone-beam computed tomography (CBCT) have been proposed as an important alternative. A recent CBCT study claims accurate examination of the impacted canine is possible in both vertical and horizontal planes along with its effect on adjacent structures.  Despite the more detailed information yielded by these techniques, the comparable higher radiation dose and cost outweigh their relative advantages. ,
The idea of utilizing single panoramic radiograph in localization was introduced by Wolf JE and Matilla K in 1979. , Accordingly, the object placed closer to the film (i.e., farther from the X-ray source) throws a smaller shadow than the object localized at a greater distance from the film and closer to the X-ray source. Thus, if the unerupted tooth is closer to the X-ray tube on one side than the corresponding tooth on the other side, it will appear larger on the panoramic radiograph.
Unfortunately, the reliability of such a system was found to be low because it did not take into consideration the distance between the radiation source and the film and its influence on the vertical location of the object on the panoramic radiograph. The vertical position of the object should be taken into consideration because as the central ray in the panoramic radiograph is directed at a negative angulation the palatally located teeth will be projected higher than the labially located teeth even though they may be at the same height above the occlusal plane. As a result, the height of the image of the tooth on the panoramic film will be exaggerated by its bucco-palatal displacement and by its vertical height above the occlusal plane.  This was evaluated by Chaushu, et al.  and they therefore suggested that expression of the vertical factor was necessary to achieve a valid magnification index.  However, the vertical position only suggests the likelihood of the placement of the impacted canine (i.e. palatal canine in the middle zone and buccal canine in the coronal zone) and hence as evident from the present study, that there is a possibility for both buccally and palatally located canines to lie in the same zone. Therefore, the magnification factor was also included in this study as suggested by Chaushu, et al.  to determine the bucco-palatal position of the impacted canine.
In the present study, when magnification index was also considered, localization in bucco-palatal position was possible in 96 out of 102 canines located in the middle and coronal zones. Localization was not possible in the remaining six canines (three in the middle and three in the coronal zones) as they showed overlapping in their CII and CCI range. By excluding them, the overall agreement in the 102 canines worked out to be 94.11%. This is in accordance with the study conducted by Hebbale et al.  in 2006 among 15 patients with impacted maxillary canines. The authors found by applying Chaushu, et al. criteria's exact location of the canines were possible in 14 out of 15 cases (93.3%).
The remaining 48 (32%) canines that lied in the apical zone were not amenable for bucco-palatal localization as they showed overlapping in their CII and CCI ranges (0.83-1.60). This is because neither the buccal plate nor the incisors are perpendicular to the palatal plane (i.e. incisor-palatal plane is 112° -118° ). As a result, apically located labial teeth may be on the same antero-posterior plane as more coronally located teeth and therefore will enlarge to a similar degree on the panoramic film [Table 2],[Table 3] and [Figure 2].
A single panoramic radiograph can serve as a reliable indicator for determining the bucco-palatal position of the impacted permanent maxillary canines when they lie in the middle and coronal zones with respect to the ipsilateral central incisor. It is recommended to explore their presence with other conventional or advanced imaging modalities when they lie in the apical zone. Further studies utilizing similar methods of localization of impacted permanent maxillary canines and confirmation with surgical exploration or advanced imaging techniques like CT or CBCT are recommended for better authentication of the results.
The authors thank Dr. Prabhakar, Department of Community Medicine, JSS Medical College and Hospital, Mysore for statistical guidance.
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