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 Table of Contents  
ORIGINAL ARTICLE
Year : 2017  |  Volume : 29  |  Issue : 2  |  Page : 100-105

Objectivity and reliability of panoramic radiographic signs and cone-beam computed tomography in the assessment of a superimposed relationship between the impacted mandibular third molars and mandibular nerve: A comparative study


1 Department of Oral Medicine and Radiology, Mamata Dental College and Hospital, Khammam, Telangana, India
2 Department of Oral and Maxillofacial Pathology, Mamata Dental College and Hospital, Khammam, Telangana, India

Date of Submission02-Nov-2016
Date of Acceptance23-Oct-2017
Date of Web Publication9-Nov-2017

Correspondence Address:
Kotya Naik Maloth
Department of Oral Medicine and Radiology, Mamata Dental College and Hospital, Giriprasad Nagar, Khammam - 507 002, Telangana
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jiaomr.JIAOMR_133_16

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   Abstract 

Aim: To evaluate the relationship between panoramic radiographic signs and cone-beam computed tomography (CBCT) in the assessment of a superimposed relationship of the impacted mandibular third molars and mandibular canal. Materials and Methods: Panoramic and CBCT images were evaluated independently to assess the relationship between the mandibular canal and the impacted mandibular third molar roots by two oral and maxillofacial radiologists. The results were tabulated and the association of panoramic radiographic and CBCT findings was analyzed using Chi-square test and Fisher's exact test. All of the analyses were carried out with PASW Statistics 18.0. Results: Panoramic radiographic findings were statistically significant with CBCT findings (P < 0.01). Cases of darkening roots without interruption and lingual cortical perforation suggested more frequent buccal placement of mandibular canals. Cases of darkening roots with interruption and complete lingual cortex perforation suggested more frequent lingual placement of mandibular canals. Conclusion: The results of the present study suggest that, although panoramic radiography is an effective method for preoperative evaluation prior to mandibular third molar extraction, its predictability is low with regards to the emergence of nerve lesions. Therefore, it is mandatory to know the true three-dimensional imaging relationship between the mandibular canal and impacted mandibular third molars. Thus, CBCT is the best method for risk assessment and planning prior to surgical procedures to prevent inferior alveolar nerve injury.

Keywords: Cone-beam computed tomography, mandibular nerve, panoramic radiographic sign, third molar


How to cite this article:
Reddy Kundoor VK, Maloth KN, Patimeedi A, Thakur M, Nomula R, Sunitha K. Objectivity and reliability of panoramic radiographic signs and cone-beam computed tomography in the assessment of a superimposed relationship between the impacted mandibular third molars and mandibular nerve: A comparative study. J Indian Acad Oral Med Radiol 2017;29:100-5

How to cite this URL:
Reddy Kundoor VK, Maloth KN, Patimeedi A, Thakur M, Nomula R, Sunitha K. Objectivity and reliability of panoramic radiographic signs and cone-beam computed tomography in the assessment of a superimposed relationship between the impacted mandibular third molars and mandibular nerve: A comparative study. J Indian Acad Oral Med Radiol [serial online] 2017 [cited 2020 Dec 5];29:100-5. Available from: https://www.jiaomr.in/text.asp?2017/29/2/100/217907


   Introduction Top


The surgical extraction of impacted third molars is one of most common and frequently performed procedures in oral surgery and results in several post-extraction complications, such as surgical extraction of an impacted mandibular third molar (IMTM) causes permanent damage to the inferior alveolar nerve (IAN) and results in sensory deficiency on the affected side.[1] Few studies have reported the incidence of IAN injury ranging from 0.5–8%.[2] There is high incidence of several conditions such as pericoronitis, caries on the distal surface of the second molar, external root resorption and odontogenic cysts, or tumors associated with impacted third molars.[3] Accurate preoperative evaluation of the relationship between the IMTM and the inferior alveolar canal (IAC) before surgery is necessary to avoid IAN injury and possibly avoid sensory impairment.[4] Radiographical closeness between the IMTM and IAC results in higher risk for IAN injury than otherwise.[5]

Panoramic radiography is frequently used as the diagnostic imaging method for its role in clinical practice. The main drawbacks of this technique is that it is a two-dimensional imaging modality with poor resolution and does not provide any information about the buccolingual direction of IAN. However, Rood and Shehab [6] identified seven radiographic signs on panoramic radiographs in their study including superimposition of the tooth roots on the canal, narrowing of the canal, interruption of the radiopaque borders of the canal, deviation of the canal, darkening of the roots, as well as deviation of the tooth roots and the bifid apex. This indicates a close relationship between the IMTM and the mandibular canal and its closeness to the buccal or lingual cortical plate. However, varying opinions have been expressed in predicting IAN injury with respect to the abovementioned radiographic signs. Many studies have suggested the risk of IAN injury with panoramic radiographic findings [4],[6],[7] with wide range of sensitivity (14.6–75%), specificity (39–97%), and positive (3–24%), and negative (97–99%) predictive values.[2],[8] In accordance with the abovementioned studies and to overcome the drawbacks of panoramic radiography, a three-dimensional (3D) imaging with cone-beam computed tomography (CBCT) is recommended for cases in which IMTM and IAC are in close proximity, so as to evaluate the bucco-lingual direction of IAN.[9]

CBCT is becoming more readily available for use in dentistry. It provides better image quality of the teeth and their surrounding structures compared to panoramic radiography.[10] Moreover, it reduces the radiation dose compared with other 3D imaging techniques and offers high spatial resolution.[11] Thus, it appears that the relationship between the IMTM to the mandibular canal is assessed more accurately with CBCT imaging. The aim of the present study was to evaluate the relationship between CBCT and panoramic radiographic signs in the assessment of a superimposed relationship of the impacted mandibular third molars and mandibular canal.


   Materials and Methods Top


A comparative study was carried out after obtaining ethical committee clearance using the panoramic radiographs which showed IMTM. The study samples consisted of 60 IMTM from 40 patients (16 males and 24 females) with a mean age of 24 years who showed a superimposed relationship of the mandibular canal and IMTM on panoramic radiograph and were referred to CBCT examination centre prior to IMTM extraction. Individuals with radiological evidence of intraosseous pathologies (e.g., cysts and tumors) associated with the IMTM were excluded from the study. All the panoramic radiographs were taken with an Orthophos XG Sirona, operating at 66 kVp, 8 mA, 14 s. CBCT scans were acquired with NewTom Cone Beam 3D imaging, operating at 120 kVp, 8 mA with a 0.25 mm voxel size and a field of view of 8 cm.

On panoramic radiographs, the relationship between IMTM and mandibular canal was evaluated according to the criteria established by Rood and Saheb.[6] In the present study, we examined three panoramic signs such as darkening of the root, interruption of the mandibular canal, and contact of canal to root: The darkening of the root indicates the increased radiolucency of the root of the IMTM where the mandibular canal crossed it [Figure 1]; the interruption of the radiopaque lines of mandibular canal wall, where it crossed the third molar [Figure 2]a; and the presence or absence of contact of mandibular canal to root [Figure 3]. The diversion and narrowing of the canal were not evaluated because they were rarely observed in a superimposed relationship between the third molar and the mandibular canal. The CBCT images were evaluated in all three dimensions to assess the position of mandibular canal, i.e., whether it is buccal, lingual, or inter-radicular relative to the IMTM [Figure 2]b and [Figure 2]c and the lingual cortical bone loss or perforated lingual plate [Figure 4]a and [Figure 4]b.
Figure 1: Cropped panoramic image showing darkening of the root where the mandibular canal crosses over root of the mandibular third molar

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Figure 2: Panoramic radiograph showing interruption of mandibular canal in relation to roots of impacted mandibular third molars on right and left side (a). CBCT showing buccally positioned mandibular canal on the left side (b) and lingually positioned on right side in relation to impacted third molars (c)

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Figure 3: Cropped panoramic image showing mandibular canal contact with the tooth (a) and noncontact with tooth (b)

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Figure 4: The lingual cortical bone loss was scored as complete lingual plate (a) or perforated lingual plate (b)

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Evaluation of images

The panoramic and CBCT images were evaluated independently to assess the relationship between the mandibular canal and IMTM by two oral and maxillofacial radiologists. When disagreement existed between the two observers, consensus was reached by discussion and sent for statistical analysis.

Statistical analysis

Intraobserver and Interobserver agreements were evaluated using kappa statistics. A k value of <0.40 was considered poor agreement, 0.40–0.59 was fair agreement, 0.60–0.74 was good agreement, and 0.75–1.00 was excellent agreement. Each panoramic radiographic finding was reported. Fisher's exact test was used to compare panoramic radiographic signs with CBCT findings. The association of panoramic radiographic and CBCT findings was analyzed using Chi-square test and Fisher's exact test. All of the analyses were carried out with PASW Statistics 18.0 (SPSS Inc., Chicago, IL, USA).


   Results Top


Panoramic radiographic signs were statistically associated with the buccolingual position of the mandibular canal relative to the IMTM roots on CBCT (P< 0.01). On panoramic radiographs, the relationship between the IMTM and mandibular canal was evaluated according to the criteria established by Rood and Saheb.[6] Darkening with no interruption indicated buccally positioned canals. Majority of cases with interruption and nondarkening indicated lingually positioned canals [Table 1].
Table 1: The relationship between panoramic radiographic signs and anatomic location of canal relative to third molar on CBCT

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The relationships between panoramic radiographic signs and the proximity of the roots to the mandibular canal were insignificant (P > 0.01) [Table 2]. Contact with the canal was more frequently observed when the interruption of the mandibular canal and darkening was seen on the panoramic radiographs. 'Separate from canals' were more frequently observed in cases of darkening without interruption. Fifteen cases showing contact with canals were lingually positioned relative to the IMTM, and 21 cases of separate from canals were buccally positioned which was statically significant (P< 0.01) [Table 3].
Table 2: The relationship between panoramic radiographic signs and the proximity of the roots to the mandibular canal on CBCT

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Table 3: The relationship between the buccolingual position and proximity of canal

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Perforation of the lingual cortex was more frequently observed in the cases of darkening without interruption of the cortical line. Complete lingual cortices were more frequently found in the cases with interruption and without darkening which was significant (P< 0.01) [Table 4]. Lingual cortical loss was more frequent in buccally positioned canals than in lingually positioned canals which was significant (P< 0.01) [Table 5].
Table 4: The relationship between panoramic radiograph signs and lingual cortical bone loss on CBCT

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Table 5: The relationship between the buccolingual position of mandibular canal and lingual cortical loss

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   Discussion Top


In dentistry, surgical removal of IMTM is one of routinely performed surgical procedures in young adults after 20 years of age. Due to the considerable variety in the relationship between the mandibular canal to an IMTM, preoperative radiographic assessment is required prior to surgical extraction to prevent IAN injury that can result in neurological complications.[2] The incidence of these neurological complications ranges from 0.2 to 1% for a permanent injury and from 3.3 to 13% for a temporary injury.[12] There is 30% incidence of damage to IAN when the third molar and the mandibular canal are in close relationship radiographically.[13] The risk of IAN injury is effectively and routinely evaluated by oral clinicians using panoramic radiography. Various limitations of panoramic imaging in assessing the position of mandibular canal in relation to IMTM are: two-dimensional imaging, absence of the cortical bone of the mandibular canal may not be clearly evident, and difficulty to determine whether its course is buccal or lingual to the roots or between the roots.[12] Multiple studies showed the negativity of sensitivity and specificity of various panoramic radiographic signs that predict IAN injury during mandibular third molar extraction; their results were inconsistent and concluded that panoramic images did not possess predictive ability to determine the relation between IAN and mandibular third molar.[14],[15] Hence, additional and more advanced 3D imaging techniques such as CBCT and CT scans, are required to clarify the accurate anatomical relationships between IAN and mandibular third molar prior to surgical extraction and there by prevent IAN injury.[12]

The IAN damage occurs more frequently during extraction of mandibular third molar when mandibular canal is positioned lingually to the third molar than buccally.[16] Thus, every oral surgeon should know the exact position of IAN prior to extraction to prevent injury.[17] In the present study, lingually positioned canals were more frequently observed in cases with the interruption of the mandibular canal, and contact with canals were more frequent in cases of lingually positioned canals than in cases of buccally positioned canals. It has been reported that nerve exposure is seen in cases with interruption of the mandibular canal wall.[18] The results of the present study were consistent with those of Jung et al.,[1] Nakagawa et al.,[19] de Melo Albert et al.,[20] and Atieh.[7] de Melo Albert et al.[20] and Atieh [7] analyzed that panoramic imaging features have shown that darkening of the third molar root where mandibular canal crosses over the root, it is strongly suggestive of a close relationship between the root and nerve causing nerve damage following third molar extraction.

In the present study, the mandibular canal was most often positioned lingually to the third molar (42%) than buccally. This is in accordance with the results of Ohman et al.[13] and de Melo Albert [20] and in contrast with the results of Maegawa et al.[21] The interrupted mandibular canal on panoramic radiographic findings showed that lingually positioned canals were more frequent, increasing risk of IAN exposure, which is in agreement with the results of Sekerci et al.[22]

An interradicular course is difficult to determine with conventional methods. However, Maegawa et al.[21] who used CT, found an interradicular course in only 4% of their cases. Tammisalo [23] used stereographic views (scanograms) and found an interradicular course in 3% of the cases. In this study, an interradicular course in 5% of cases were found.

In some cases, darkening of the roots could be associated with perforation or thinning of the lingual cortex by the tooth roots, instead of being related to a “true contact” relationship between the mandibular canal and tooth roots.[24] In this study, darkening with mandibular canal interruption showed more perforated lingual cortex than nondarkening interruption. Monaco et al.[25] evaluated the reliability of panoramic imaging in assessing the relationship between the mandibular canal and roots of the mandibular third molar based on CT images. According to the authors, the 3D examination should be carried out when darkening of roots, narrowing of the mandibular canal, and interruption of white line is observed on panoramic radiograph. In the present study, diversion and narrowing of the canal were not evaluated because they were rarely observed in a superimposed relationship between the third molar and the mandibular canal. It has been observed that only 3D examinations, that is CT [12] and magnetic resonance imaging,[26] are effective in determining the exact relation between the tooth roots and the mandibular canal. However, in view of the socioeconomic status, the high cost, and the radiation dose (for CT only), the use of panoramic radiography in preoperative evaluation in the third molar surgery is clearly justified, even though it has low predictability in judging emergence of nerve lesions during the procedure.


   Conclusion Top


Panoramic radiography is an effective method for the preoperative assessment of IMTM. Darkening of roots and interruption of canal can be observed on panoramic radiographs, however, exact buccolingual position of canal to the tooth roots cannot be assessed by panoramic radiography. CBCT is the best method to determine the true 3D imaging relationship between the mandibular canal and impacted mandibular third molars. Thus, it can be used for risk assessment and planning prior to surgical procedures to prevent IAN injury.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
   References Top

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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]



 

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