|Year : 2014 | Volume
| Issue : 1 | Page : 15-20
Buccal-lingual localization of the mandibular canal in relationship with the third molar using the lateral oblique technique
Gainer Raul Jasa1, Mariana Boessio Vizzotto2, Priscila Fernanda da Silveira2, Heloisa Emilia Dias da Silveira2, Heraldo Luis Dias da Silveira2, Leticia Ruhland Correa2, Tabare Raveca1
1 Oral Radiology Division, Universidad de La República Uruguay, Montevideo, Uruguay
2 Department of Surgery and Orthopedics, Oral Radiology Division, Dental School, Federal University of Rio Grande do Sul, Porto Alegre, Brazil
|Date of Web Publication||2-Jun-2014|
Mariana Boessio Vizzotto
Rua Ramiro Barcelos 2492 - 5th floor, CEP 90035 - 000, Porto Alegre, Rio Grande do Sul
Source of Support: None, Conflict of Interest: None
Aim: The aim of this study was to evaluate the use of lateral oblique radiography (LOR) at two different incidence angles for the bucco-lingual topographic localization of the mandibular canal with respect to the lower third molars. Materials And Method: A total of 24 dry jaws bearing at least one third molar were subject to LOR at vertical incidence angles of 0° and -30°. A trained and calibrated examiner measured the distance between the top of the mandibular canal to the most apical point of the third molar, using a digital calliper and individual light box for the radiographs. Based on the analysis of the two measurements (incidence angles of 0° and -30°) and considering the buccal object rule, the observer estimated the location of the mandibular canal, which was classified as lingual, central or buccal to the corresponding third molar. Results were compared with the computerized tomography images (gold standard). Results: The statistical analysis included sensitivity, specificity and accuracy tests. These results showed that LOR (0° e -30°) could be used to determine the bucco-lingual location of the mandibular canal with respect to the third molar. Conclusion: In spite of the magnification, LOR images demonstrated that the technique could be used for this study proposal.
Keywords: Computerized tomography, lateral oblique radiography, mandibular canal
|How to cite this article:|
Jasa GR, Vizzotto MB, da Silveira PF, da Silveira HD, da Silveira HD, Correa LR, Raveca T. Buccal-lingual localization of the mandibular canal in relationship with the third molar using the lateral oblique technique. J Oral Maxillofac Radiol 2014;2:15-20
|How to cite this URL:|
Jasa GR, Vizzotto MB, da Silveira PF, da Silveira HD, da Silveira HD, Correa LR, Raveca T. Buccal-lingual localization of the mandibular canal in relationship with the third molar using the lateral oblique technique. J Oral Maxillofac Radiol [serial online] 2014 [cited 2019 Feb 19];2:15-20. Available from: http://www.joomr.org/text.asp?2014/2/1/15/133557
| Introduction|| |
Surgical removal of lower third molar is a common procedure in clinical dental practice ,,, and could be associated with post-operative complications related to inferior alveolar nerve injuries. Permanent nerve injury amounts between 0.2% and 1% of surgeries, while the temporary injury is between 3.3% and 13%, ,,,, and increases around 30% when third molar root is in direct contact with the inferior dental nerve.  Consequently, a specific evaluation of the mandibular canal and the proximate molars is essential during pre-operatory planning.
Considering different positions of the lower third molar (LTM), and because its relative position in respect of the mandibular canal (MC) differs according to the patient, several imaging methods could be used for the diagnosis. Panoramic radiograph is usually used as radiographic method of examination for third molar removal treatment planning, due to its wide availability, low cost and relatively low exposure dose. ,,,, Periapical technique could be used for pre-surgical evaluation of lower third molars, , however film position could be uncomfortable and compromise the diagnosis.  It should be observed that bucco-lingual aspect couldn't be visualized using panoramic and periapical techniques. A limitation associated with these techniques is that they provide a two-dimensional image.  By using the vertical tube shift method, the clinician who uses two radiographs taken at different vertical angulations may be able to clarify some of the diagnostic uncertainties that the panoramic radiograph or the periapical radiograph alone cannot solve. 
Cross-sectional or conventional computed tomography was used in the dental practice before the introduction of cone-beam computed tomography (CBCT).  Due to the recent development of CBCT, three-dimensional images are becoming more easily available in dentistry, allowing extra investigation of MC and surrounding molars.  This technique provides non-superimposed full-size images on the three spatial planes. ,,, Some disadvantages of CBCT are related to the high radiation dose compared with the conventional radiography, the high cost of equipment and the limited accessibility. ,,,
Lateral oblique radiography (LOR) is an extra-oral technique referred to as lateral oblique mandibular view. In some situations LOR is the favored technique in view of the low cost and the low patient radiation dose; this radiography technique could be use by the vertical tube shift method.
LOR radiographs as other techniques show some distortion in consequence of the divergent trajectory of X-ray photons; , and distortion increases when using the vertical tube shift method due to the change of the vertical angulation of the x-ray beam. As a result, the surgeon must be well acquainted with this magnifying effect. It should be noted that the dimensional reliability of pre-surgical radiographic tests has been reported to be the primary determinant of the post-surgery success of the overall dental procedure. 
In view of the necessity to establish the dental position and its relation with mandibular canal, some authors, based on the ALARA principle, recommended the use of radiographic localization methods. ,, Thus, this study aimed to evaluate a LOR, based on the vertical tube displacement technique (VTDT) using two different incidence angles to determine the position of the mandibular canal and lower third molar and moreover, to evaluate the linear measures distortions, using CT images as the gold standard.
| Materials and Methods|| |
This cross-sectional study was conducted with a total of 24 jaws and 37 third molars selected from the Anatomy Museum of UdelaR School of Dentistry. This research was approved by the Ethics Committee of UdelaR's School of Dentistry.
Two lateral oblique radiographs were obtained of each third molar with a distinct vertical angle (0° and -30°, respectively) [Figure 1]. The X-rays beam was directed to the retro mandibular space  located at the intersection of the posterior margin of the mandibular ramus and a horizontal line extended posteriorly from the basal mandibular bone.  The jaws were placed in a standard device and the image receptor in parallel position and direct contact with the ramus and mandibular body under study. LORs were acquired on a Kodak 2200 intra-oral system (exposure values of 70 Kv, 7 mA and 0.01 s). An 18 × 24 cm Kodak radiographic film was used. The exposed film was manually processed. Axial tomograms (SOMATOM Siemens AG Medical Solutions, Erlangen, Germany, 64-channel, 120 Kv and 90 mA) were obtained of each of the jaws in a standard position, with a slide distance of 0.5 mm. These images accounted the gold standard. The examiner had a calibration run up.
|Figure 1: Two lateral oblique radiographs obtained of each third molar with a changed vertical angle (0° and – 30°, respectively)|
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Radiographic and tomographic evaluation
A trained and calibrated examiner (Kappa > 0.8) made the measures, two times with an interval of 15 days. The 0° LOR was firstly evaluated followed by -30°, measuring the distance from the most apical point of the third molar to the most superior point of the mandibular canal. The evaluations were made on a light box using a digital calliper. Based on the radiographic localization method, the relationship between the mandibular canal and the third lower molar was classified as lingual, central or buccal position, established by the value found: Decrease, unchanged or increase. The minimum unit considered was 0.2 mm, based on the resolution capacity of the human eye.  The analyses were repeated with a 15-day time interval.
Osirix free software (Geneva, Switzerland) was used to evaluate three-dimensional analysis and establish the gold standard. Coronal plane was considered to be the most appropriate to analyze the images and determinate the mandibular canal position. 
To establish the linear measures distortion, marks were made on the radiographs and tomograms, showing the crown equator and the crown-radicular length of third molars (tooth length). The distance between the distal alveolar crest of the third molar, determined vertically until the mandibular basis and horizontally until to the posterior margin of the mandibular ramus [Figure 2]. If the distal crest of the third molar could not be considered due to intra-osseous insertion, the distal alveolar crest of the lower second molar was used. Four linear measures were made on all radiographs with a digital calliper on a light box, totaling 12 measurements. The gold standard was defined by the tomograms using Osirix software tools.
|Figure 2: The lateral oblique radiographs and tomogram showing the crown equator, the crown-radicular length of third molars (tooth length), the distance between distal alveolar crest of the third molar until mandibular base (vertical) and until posterior margin of the mandibular ramus (horizontal)|
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R Software (version 2.15.3) was used to run statistical analysis. Sensitivity, specificity, positive predictive values, negative predictive values and accuracy values were calculated based on gold standard. The intra-observer reliability was assessed by kappa values.
Radiographic distortion was evaluated using the paired t-Student test, with P ≥ 0.05; P < 0.05( * ); and P < 0.01( ** ).
| Results|| |
Two of the 37 third molars were not evaluated because the incapability to observe the mandibular canal. The distribution of the mandibular canal location, determined by the tomographic images (gold standard) was: Central = 9 (25.7%), lingual = 3 (8.6 %) and buccal = 23 (65.7 %).
[Table 1] and [Table 2] show sensitivity and specificity, positive and negative predictive values and accuracy for the two LOR evaluations. Accuracy of intra-observer agreement was between 0.943 and 0.971. A high degree of intra-observer agreement was found between the first and second evaluations, with kappa = 0.832.
|Table 1: Sensitivity, specificity (in parentheses) and accuracy for the third lower molar localization in the first and second LOR evaluation|
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|Table 2: Positive and negative (in parentheses) predictive values for the third lower molar localization in the first and in the second LOR evaluation|
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Sensitivity and specificity, as well as positive and negative predictive values of intra-observer agreement are displayed in [Table 3]. As in [Table 4], a comparison of the -30° and 0° LOR shows a higher distortion in vertical measurements. Considering that measurements of tooth length and body are vertical and that those of crown and ramus are horizontal, a higher degree of distortion by magnification was observed in vertical measurements, as shown in [Table 5].
|Table 3: Sensitivity, specificity, positive and negative predictive values of intra-observer agreement|
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|Table 4: Distortion (percentage) for the two lateral oblique radiographs (– 30° and 0°)|
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|Table 5: Distortion of the measurements made on the lateral oblique radiographs in comparison with computed tomography (CT) results|
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| Discussion|| |
Third molar extraction is the surgical procedure most frequently conducted by dentists and dental surgeons. An imaging exam is indicated prior to surgery to assess the relation of the LTM with the MC, aiming to avoid any damage to the inferior alveolar nerve. ,,, Panoramic radiography is the chosen exam, ,,,,, followed by intra-oral periapical radiography. , Although those exams allow an evaluation of tooth position and an estimation of its proximity to the MC, a bucco-lingual appreciation of the MC and the identification of direct contact between structures are not possible.
In this situation, some authors ,, recommended the use of CBCT for a deep assessment of the relation between ITM and the MC. In spite of the reduced radiation dose when compared to the fan beam CT, , its radiation is higher than a radiographic exam.  Besides, the availability of CBCT units is still limited in some places. Therefore, this study aimed to test a low radiation exam available for a population that do not have access to panoramic or CBCT units. Also, a variation in the LOR technique allowed an evaluation of the bucco-lingual position of the MC.
No previous studies have reported on the use of the parallax principle on the vertical plane for establishing the bucco-lingual relationship of the MC with respect to the LTM. The results from this study demonstrated that the LOR-proposed technique is highly effective to classify the MC as lingual, central or buccal in relation to the LTM. Ghaeminia et al. observed that lingual positioning of the MC is significantly linked with injuries to the IAN, showing the importance of this assessment before surgery.
Kositbowornchai et al. suggested the use of CBCT if a panoramic radiograph combined with periapical technique with vertical tube shift method does not provide sufficient information, or when it is not possible to conduct an intra-oral exam. According to the results from this study, the LOR does not cause patient discomfort, and may be considered prior to the CBCT indication.
One disadvantage of the use of LOR, compared with CBCT, is associated with image distortion or magnification, since CBCT provides non-superimposed real-size images on the three spatial planes. ,,,, However, compared with panoramic radiography - reported magnification values between 20% and 30% for the posterior mandible region ,,, - the distortion values found in this study - in order of 15% and 26.5% when angulations of 0° and -30° were used, respectively - suggest that LOR can be used successfully, with LOR at 0° resulting in a smaller degree of distortion than panoramic radiography.
Kositbowornchai et al. compared the ability of two radiographic methods: The panoramic radiograph in combination with a 20-degree negative angle periapical radiograph versus two periapical radiographs 0° and -20°, in evaluating the closeness of the lower third molar root and the mandibular canal. The present study obtained specificity and sensibility values much higher than Kositbowornchai et al. study.
Because the distance between the MC and the ITM is small, and occasionally both are superimposed, it is necessary to change the vertical angle to a minimum of -30° in the second acquisition in order to observe the apparent movement of the MC in the radiographic image. However, LOR at −30° resulted in appreciable distortion, amounting to up to 26.5% of the tooth length. Thus, those images should be interpreted with extreme care based on understanding of the particular image acquisition principles.
Neugebauer et al. compared the diagnostic value of conventional radiologic procedures using a panoramic radiograph and symmetrical PA cephalometric radiograph convened with that of a CBCT device for identifying the position of the root tip in relation to the alveolar nerve. The difference between the diagnostic information for the horizontal dimension was highly significant (P = .000), with an advantage for the CBCT. In our study, the diagnostic information for the horizontal dimension showed no significant difference between convened LOR and CT, with a highly significant accuracy (P = 0.0000752).
On the other hand, 9.0% of the MC could not exactly be determined in the conventional radiographic group and 2.8% could not be determined exactly at CBCT in the Neugebauer et al. study.
In the study by conducted by Suomalainen et al.,  in cross-sectional tomography, the MC was graded as invisible or the evaluation unreliable in 41% (reader 1) and 28% (reader 2) of the cases.
In the present study, in 5, 4% of the cases the MC could not be exactly identified showing that LOR is an imaging method that provides precise location of the MC. The results of this study allowed the assessment of the ITM with a low cost, good image quality and, more important, low radiation dose technique. Therefore, LOR at incidence angles of 0° and -30° may be successfully used to determine the bucco-lingual relationship between the mandibular canal and the lower third molar.
| Acknowledgments|| |
The authors thank the authorities of UdelaR and UFRGS for an agreement signed between both institutions that made this study possible.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]