|Year : 2019 | Volume
| Issue : 1 | Page : 93-98
Comparison of conventional techniques and higher imaging modalities in the evaluation of relation between the third molar and inferior alveolar nerve canal: A pilot study
Vathsala Patil1, Keerthilatha M Pai1, R Vineetha1, KV Rajagopal2, Winniecia Dkhar3
1 Department of Oral Medicine and Radiology, Manipal College of Dental Sciences, Manipal, Karnataka, India
2 Department of Radio-Diagnosis, Kasturba Medical College, Manipal, Karnataka, India
3 Department of Medical Imaging, School of Allied Health Sciences, Kasturba Medical College, Manipal Academy of Higher Education, Manipal, Karnataka, India
|Date of Web Publication||17-Dec-2019|
Dr. Keerthilatha M Pai
Department of Oral Medicine and Radiology, Manipal College of Dental Sciences, Manipal Academy of Higher Education, Manipal - 576 104, Karnataka
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Context: Mandibular third molars are the most commonly impacted teeth, and their surgical removal can be associated with inferior alveolar nerve (IAN) injury. To avoid the deleterious complication of nerve injury on patients, a thorough visualization of IAN and its localization are essential. Aims and Objectives: The aims and objectives of this study were to evaluate the efficacy of two conventional localization techniques in determining the relationship of mandibular third molars to IAN and to assess its reliability in comparison with computed tomography (CT). Settings and Design: Panoramic radiograph (PR) was taken using Kodak 8000C Digital Panoramic and Cephalometric system. Intraoral periapical radiographs (IOPAs) were taken using Kodak 2200 Intraoral X-ray machine. CT scan images were taken using multidetector CT scans. Materials and Methods: Two IOPAs (0° and −20° vertical angulation) and PR and CT scan images of thirty mandibular third molars were taken. Two combinations were used (i) a combination of two IOPAs and (ii) a combination of PR and IOPA (−20°). Tube-shift localization technique was applied to both these combinations to derive the relation between third molar and IAN canal as “in contact,” “separate,” “buccal,” “lingual,” and “in line with the apex” and the results were compared with CT images. Statistical Analysis: Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were calculated using SPSS software version 15.0. Results: The combination of PR and IOPA radiographs showed 14 teeth to be in contact with IAN. This gave a sensitivity of 100%, specificity of 94.1%, PPV of 92.9%, and a NPV of 100% in determining the relation as “in contact” or “separate.” 78.3%, 85.7%, 94.7%, and 54.5% were the sensitivity, specificity, PPV, and NPV in localizing it as “buccal,” “lingual,” or “in line with apex.” These results were better than that of the combination of the two IOPAs. Conclusions: Localization using PR and IOPA could better deduce the relation between IAN and mandibular third molar.
Keywords: Localization, mandibular nerve, mandibular third molar, panoramic radiography
|How to cite this article:|
Patil V, Pai KM, Vineetha R, Rajagopal K V, Dkhar W. Comparison of conventional techniques and higher imaging modalities in the evaluation of relation between the third molar and inferior alveolar nerve canal: A pilot study. Contemp Clin Dent 2019;10:93-8
|How to cite this URL:|
Patil V, Pai KM, Vineetha R, Rajagopal K V, Dkhar W. Comparison of conventional techniques and higher imaging modalities in the evaluation of relation between the third molar and inferior alveolar nerve canal: A pilot study. Contemp Clin Dent [serial online] 2019 [cited 2020 Apr 10];10:93-8. Available from: http://www.contempclindent.org/text.asp?2019/10/1/93/273156
| Introduction|| |
Mandibular third molars are the most commonly impacted teeth with a frequency of 20%–30%. Their surgical removal can be associated with various postprocedural complications; one among them is the inferior alveolar nerve (IAN) injury. The risk of IAN damage increases dramatically by 30%, when there is contact or a close relation between the tooth and the nerve. Therefore, to avoid the deleterious complication of nerve injury on patients, a thorough visualization of IAN and its localization are essential not only for third molar extraction, but also for implant placement and sagittal split osteotomy procedures.
Intraoral periapical radiographs (IOPAs) and panoramic radiographs (PRs) were the most common conventional two-dimensional (2D) imaging techniques used for localization of IAN canal. However, with the advent of three-dimensional (3D) imaging such as computed tomography (CT) and cone-beam CT (CBCT), these modalities have become the primary choice of imaging for surgeons. However, is it justified to use higher imaging modalities, exposing patients to higher radiation exposure and high cost for simple cases with no absolute indication, is a debatable issue of the hour.
Previous studies comparing conventional and advanced imaging have shown different results. When authors like Klinge et al., Lindh et al., Ylikontiola et al., and Sonick et al. have concluded that 3D imaging is very essential for IAN visualization, studies by Pawelzik et al. and Nakagawa et al. showed conventional imaging to be as good as 3D advanced imaging. Since IOPA and PR are routinely used in our setup, we conducted this study with an aim to evaluate the efficacy of two conventional localization techniques in determining the relationship of mandibular third molars to IAN and to assess its reliability in comparison with CT images as gold standard. Only two studies have been done in the past, using vertical tube-shift technique; hence, a need for confirming this unique and simple localization technique as a replacement for advanced imaging modality was identified.,,
| Materials and Methods|| |
This study was conducted for 6 months after obtaining approval from the Institutional Ethical Committee. Twenty dry human mandibles, in good condition and intact lower border, having a total of thirty third molars (unilateral or bilateral), were selected. Mandibles with irregular lower border where stabilization was not possible, missing third molars, molars with periapical lesions revealed on radiographic images, and unaccepted quality of radiographic images were all excluded from the sample size.
Mandibles were given a code from 1 to 20 for identification and underwent the following radiographic examinations:
- Digital PR using Kodak 8000C Digital Panoramic and Cephalometric system at exposure parameters of 66 kVp, 12 mA, and 14 s. The mandibles were positioned on the chin rest of the machine using thermocol base and adhesive tapes, simulating the position of the patient [Figure 1]. Central beam and canine beam were oriented to the midline and canine regions, respectively
- IOPA using Kodak 2200 Intraoral X-ray machine. Two radiographs were taken of each mandibular third molars, one with 0° vertical angulation (0° IOPA) taken in paralleling technique and second with −20° vertical angulation (−20° IOPA) using E speed film. The mandibles were stabilized on the same thermocol base used for PR [Figure 2]. The exposure parameters were 60 kVp, 7 mA, and 0.25 s, and the exposed films were processed using an automatic processor
- CT imaging in a Philips 64 slice Multidetector CT scanner (Philips medical systems, The Netherlands). Each specimen was placed on a custom-made thermocol stand in a way that the lower border of the mandible was perpendicular to the floor. High-resolution, 1-mm-thick slices with 1-mm/s table feed (5-mm reconstruction); 120 kVp and 160 mA tube current; and field of view 12 cm with a 512 × 512 matrix was all constituted the scanning protocol. The data were transferred for postprocessing using Dental CT reformation software (Philips medical systems, The Netherlands).
|Figure 2: Stabilization of the mandible while taking intraoral periapical radiographs|
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Radiographic techniques used for localization
- Localization technique 1 (LT 1) – Combination of two IOPAs with 0° and −20° vertical angulation
- Localization technique 2 (LT 2) – Combination of PR with −20° vertical angulation.
All the images were subjectively evaluated by two trained observers considering the tip of the mandibular third molar root as the reference point. The images were viewed in a room with reduced ambient light wherein the peripheral light from the view box was masked. Using the two techniques and applying Richards buccal object rule of localization, the relation between the IAN and third molar root was interpreted as follows: (a) in contact or separate and (b) central, buccal, or lingual.
Interpretation of localization techniques applying Richards buccal object rule
Richards buccal object rule states that “When two radiographs are made of a pair of objects, the image of buccal object moves, relative to the image of lingual object, in the same direction as that of the X-ray beam.” In LT 1, if the IAN canal appeared to move in the upward direction in −20° IOPA, in comparison to 0° IOPA, applying Richards buccal object rule, as canal moved along the direction of the beam, its relationship with respect to the mandibular third molar was localized to be “buccally” placed. If the canal moved downward (i.e., in the opposite direction of the beam), then it was localized to be “lingually” placed. If the canal showed no movement on the radiographs, it was localized to be in the “central” position or in the same plane as the third molar.
In LT 2, the projection of the X-ray beam in PR is from the lingual aspect; for ease of interpretation, it was translated to be from the buccal aspect, which yields a positive +8° as illustrated in [Figure 3]. Thus, interpretation was done in the similar way as LT1 considering two different projection angles of +8° and −20°.
|Figure 3: The interpretation of panoramic radiograph, the X-ray beam considered to be from the buccal aspect with positive vertical angulation|
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- The results of LT1 and LT 2 were compared with the gold standard – CT images, and their sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were calculated
- Statistical Package for the Social Sciences SPSS 15.0, (IBM SPSS Statistics software, Chicago, USA) was used for statistical evaluation.
| Results|| |
Out of the twenty mandibles, thirty third molars were considered for the study. Two trained observers, with good interobserver agreement (Kappa value for LT 1 is 0.92 and for LT 2 is 0.95), evaluated all the images. The recorded relation was compared with the findings of gold standard CT images.
Findings showing the relationship between IAN canal and mandibular third molar, detected from CT images and the two localization techniques, are presented in [Table 1]. [Table 2] and [Table 3] show comparison between both the techniques and gold standard CT in detecting the relation between the canal and tooth. The mean sensitivity of LT1 and LT 2 in detecting the relation as “contact” and “separate” was 92.3% and 100%, respectively. The mean specificity of LT 1 and LT 2 in detecting the relation as separate was 88.2% and 94.1%, respectively. The mean sensitivity of LT 1 and LT 2 in detecting the relation as “buccal,” “lingual,” and “in line of apex” was 69.6% and 78.3%, respectively. The mean specificity of LT1 and LT 2 in detecting the relation as “buccal,” “lingual,” and “in line of apex was 57.2% and 85.7%, respectively.
|Table 1: Localization of inferior alveolar nerve canal as “separate,” “in contact,” “central,” “buccal,” and “lingual”|
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|Table 2: Comparison between localization technique 1 and localization technique 2 and gold standard in determining contact between third molar and inferior alveolar canal|
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|Table 3: Comparison between localization technique 1 and localization technique 2 and gold standard in determining relation between third molar and inferior alveolar canal as “central,” “buccal,” or “lingual”|
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| Discussion|| |
IAN injury is a common and deleterious complication of third molar extraction which can be avoided by understanding the IAN nerve-to-tooth relation. IOPA and Panoramic Radiographs (PRs) are the conventional imaging techniques used for evaluating the nerve-to-tooth relation. However, as these provide images in two dimensions, surgeons often choose 3D imaging techniques such as CT and CBCT. CBCT, since the time of its introduction, has become the indispensable third eye of dentistry. Even though CBCTs and CTs are more accurate in localization, they pose high radiation risk to the individual. The relative exposure of CBCT is about 4–42 times than single PR and CT which accounts to 25–800 times higher relative exposure. Therefore, their hyped and injudicious use subjects individuals to unnecessary radiation risk. Henceforth, a shift from as low as reasonably achievable to as low as diagnostically acceptable is very important. Studies by Klinge et al., Lindh et al., Ylikontiola et al., and Sonick et al. have compared conventional radiographic techniques with higher imaging modalities such as CT, CBCT, and high-resolution CT in the visualization of IAN canal and have found the higher imaging modalities to be more accurate. Sonick et al. have found periapical radiographs to give better visualization of inferior alveolar canal compared to PRs. However, Neugebauer et al., Ghaeminia et al., and Pawelzik et al. have considered the diagnostic quality of PR images equal to that of CT and CBCT and have dissented the regular use of the higher imaging techniques such as CT and CBCT prior to all the third molar surgeries. Localization principle in dentistry helps us to deduce a 3D information from the two-dimensional imaging modalities. This principle which is frequently used to localize the position of impacted teeth can be used for assessing IAN-to-tooth relation. Till date, only three studies have evaluated the use of localization technique, out of which only two studies evaluated the vertical tube-shift technique.,, Hence, this study was conducted to evaluate the efficacy of conventional imaging modality in comparison with higher imaging modality in deriving the relation between IAN canal and third molar using localization principle.
Out of the thirty third molars evaluated, IAN canals were clearly visualized bilaterally on all the mandibular CT images and IOPAs. Only one PR failed to show distinctly the upper cortical outline of the inferior alveolar canal; however, the band of radiolucency was considered as the nerve canal in this case for interpretation. CT images revealed 43.3% of teeth to be in contact with the IAN canal and 56.7% of teeth to be separate. Nakagawa et al. reported 76.7% of the teeth to be in contact with the nerve and Kositbowornchai et al. reported 68.6% of teeth to be in contact with the third molar.
LT 1, which used a combination of two IOPAs, revealed 14 teeth to be in contact with IAN, while 16 teeth were found to be separate. When compared with gold standard, the sensitivity was 92.3%, specificity was 88.2%, PPV was 85.75%, and NPV was 93.38%. The study by Kositbowornchai et al. also used the combination of two IOPAs for localization and showed a sensitivity of 84.8% and a specificity of 44.4%, a PPVof 78.3%, and a NPV of 78.3%.
LT 2, which used a combination of PR and IOPA, showed 14 teeth to be in contact with IAN, while 16 teeth were found to be separate. This gave a sensitivity of 100%, a specificity of 94.1%, a PPV of 93.8%, and a NPV of 100%. The study by Kositbowornchai et al. reported a sensitivity of 97.9% and a specificity of 100%. When the two techniques of localization used in our study were compared with the study done by Kositbowornchai et al., our study showed both the techniques to have an excellent ability to identify the true negatives and therefore, less chance for mistakenly reading the relationship between mandibular third molar and IAN as “in contact” when it should be “separate.”
Lubbers et al. in their study also observed the course of IAN to be situated buccally in 52.8%, lingually in 37.3%, and inter- or intra-root in 10%. In our study, 76.6% of teeth on CT images showed inferior alveolar canal to be in line with the apex and the remaining teeth of 23.4% to be buccally placed, and none of the teeth showed a lingually placed IAN. The difference between our study results pertaining to the course of IAN could be due to the difference in the sample size of mandibular teeth being evaluated.
The sensitivity of LT 1 in localizing the position of the inferior alveolar canal as “buccal” or “central or in the same plane” with respect to third molars was 69.6%. The specificity, PPV, and NPV were 57.1%, 84.2%, and 36.4%, respectively. Kositbowornchai et al. evaluated the sensitivity for each position (buccal, lingual, and in line with the apex) separately using a combination of two IOPAs. They found a sensitivity of 85.7% and a specificity of 38.9% in identifying the relation as buccal, a sensitivity of 50% and a specificity of 100% in identifying the relation as lingual, and a sensitivity of 31.3% and a specificity of 81.3% in identifying the position as in line with the apex. Their mean sensitivity was 55.6% and specificity was 73.4%. Our results showed better sensitivity but a slightly low specificity when compared to those of Kositbowornchai et al.
When LT 2 was compared with the gold standard in localization of the position of IAN canal as “buccal” or “central or in the same plane,” the sensitivity, specificity, PPV, and NPV were 78.3%, 85.7%, 94.7%, and 54.5%, respectively. The average sensitivity and specificity reported by Kositbowornchai et al. for a combination of PR and IOPA were 52.83% and 69.2%, respectively. Our results exhibited excellent sensitivity and specificity compared to the previous study.
Images of tube-shift technique depend on various factors such as the distance between the third molar root and inferior alveolar canal and tube movement. Greater shift of the inferior alveolar canal is seen if the distance between the third molar and inferior alveolar canal is more. If there is no movement of the canal, the inferior alveolar canal is considered to be in contact with the third molar root. Similarly, if the tube movement is larger, shift of the image also is more. Hence, tube movement between PR and −20° periapical radiograph had greater difference in incidence angle compared to two different angled periapical radiographs and showed different results.
In our study, we found LT 2, a combination of PR and negative 20° vertical angulation, to have better sensitivity, specificity, PPV, and NPV when compared to that of LT 1. This could be attributed to the following reasons:
- In LT 2, digital panoramic images of all the mandibles were obtained, which added advantage by providing better images with optimum density and contrast and less processing errors
- As the images here were digital, they could be magnified to clearly view the region of interest; hence, better visualization was possible
- Difference in the incidence angle of the X-ray beam was more when PR and –20° periapical radiograph were considered, as compared to the incidence angles used in taking two periapical radiographs. Hence, even minor movement in the IAN canal could have been clearly visualized and correctly interpreted.
Thus, we believe that conventional imaging with localization techniques has to be essentially used to assess the relation of third molar to nerve prior to advising for any higher imaging modalities with high radiation exposure.
This was an experimental in vitro study conducted on human mandibles. Extrapolating the results of this study to real-life clinical situations will need consideration of patient positioning. Patient positioning while taking PR plays a vital role. During PR, the structures that lie outside the focal trough have poor definition. Change in the vertical head position may depict variation in the relationship between the inferior alveolar canal and the third molar root due to change in the path of X-rays. Hence, a good knowledge and understanding of direction of the beam and image formation is required for correct interpretation. According to Stromotas et al., vertical tilting of head up to 10° has no effect on the linear and angular measurements, beyond which there can be distortion.
Limitations of this pilot study were the comparison of two different localization techniques and judgment of the movement of the IAN canal was made subjectively. Objective measurement of the distance between the root tip and IAN would be more accurate. Furthermore, this was an in vitro pilot study; further studies on a large number of symptomatic patients, using optimum negative angulations to validate the reliability of these techniques, should be done.
| Conclusion|| |
Combination of Panoramic Radiograph and –200 periapical radiograph showed more accurate results in localizing the relation between the inferior alveolar nerve and the mandibular third molar in comparison to CT images. Hence IAN canal imaging with conventional techniques should be a priority before advising higher imaging modalities, with higher radiation exposure like CT, CBCT.
We would like to acknowledge the Department of Radiodiagnosis, KMC Manipal, and Department of Medical Imaging Technology, SOAHS, Manipal, for their technical support. We are also grateful to Dr. Kalyan C. Pentapati, Associate Professor, Department of Public Health Dentistry, MCODS, Manipal, for the statistical help rendered during this study.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3]