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 Table of Contents  
ORIGINAL ARTICLE
Year : 2018  |  Volume : 15  |  Issue : 1  |  Page : 33-38

Assessment of Roods and Shehab criteria if one or more radiological signs are present in orthopantomogram and position of the mandibular canal in relation to the third molar apices using cone beam computed tomography: a radiographic study


1 ITS Centre for Dental Studies and Research, Muradnagar, Uttar Pradesh, India
2 Sri Ramachandra University, Faculty of Dental Sciences, Chennai, Tamil Nadu, India
3 ITS Centre for Dental Studies and Research, Greater Noida, Uttar Pradesh, India
4 Panineeya Institute of Dental Sciences and Research Centre, Hyderabad, Telangana, India

Date of Submission09-Oct-2017
Date of Acceptance10-Jan-2018
Date of Web Publication4-Apr-2018

Correspondence Address:
Rajeev Pandey
Department of Oral and Maxillofacial Surgery, ITS Centre for Dental Studies and Research, Muradnagar, Uttar Pradesh
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/tdj.tdj_53_17

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  Abstract 

Aim
The aim was to access Roods and Shehab criteria if one or more radiological signs are present in orthopantomogram and position of the mandibular canal in relation to the third molar apices using cone beam computed tomography (CBCT).
Materials and methods
A total of 25 orthopantomogram radiographs exhibiting close relationship between mandibular third molar apices and mandibular canal according to Roods and Shehab criteria were accessed for cortical integrity along with position of the canal using CBCT.
Results
CBCT images showed that about 63.8% of the teeth were in contact (loss of cortical integrity) with mandibular canal. All Teeth with two or more radiological signs showed contact. The position of the canal was buccal in 61.7% of cases followed by inferior placement in 23.4% of the cases.
Conclusion
Risk of injury to inferior alveolar nerve increases if two or more radiological signs are present. In our study buccally placed inferior alveolar nerve was seen in more often therefore operator should not gutter the bone below the middle third of the root and mesial point of application for elevation should be used in cases with radiological signs of close association between the nerve and the root apex.

Keywords: cone beam computed tomography, inferior alveolar nerve, orthopantomogram, third molar


How to cite this article:
Pandey R, Ravindran C, Pandiyan D, Gupta A, Aggarwal A, Aryasri S. Assessment of Roods and Shehab criteria if one or more radiological signs are present in orthopantomogram and position of the mandibular canal in relation to the third molar apices using cone beam computed tomography: a radiographic study. Tanta Dent J 2018;15:33-8

How to cite this URL:
Pandey R, Ravindran C, Pandiyan D, Gupta A, Aggarwal A, Aryasri S. Assessment of Roods and Shehab criteria if one or more radiological signs are present in orthopantomogram and position of the mandibular canal in relation to the third molar apices using cone beam computed tomography: a radiographic study. Tanta Dent J [serial online] 2018 [cited 2018 Jun 21];15:33-8. Available from: http://www.tmj.eg.net/text.asp?2018/15/1/33/229247


  Introduction Top


Damage to inferior alveolar nerve (IAN) can manifest as transient sensory disturbances such as paresthesia, hypoesthesia, dysaesthesia, and sometimes prolonged anesthesia [1],[2],[3],[4]. Incidence of transient sensory disturbance ranges from 0.4 to 6% and 0.2 to 1% for permanent damage [1],[2]. Injury to the nerve can occur directly by surgery if the nerve is placed buccally or high up in deeply impacted teeth [5]. Nerve can get injured indirectly, during unfavorable movements of the third molar roots during luxation of the tooth in apical, buccal or lingual directions [6]. Sometimes there is direct grooving of the root by the nerve which increases the nerve injury if the tooth is removed. Therefore the risk increases when there is close relation between the nerve and the root of the tooth [2],[7].

The topographic relationship of the third molar root apices and mandibular canal should be evaluated to reduce IAN injury. The topographic relation is evaluated using different imaging techniques. Orthopantomogram (OPG) is one of the widely used techniques. According to Roods and Shehab various radiographic markers are present in OPG indicating close relationship between the third molar and the mandibular canal, for example darkening of root, deflection of root, narrowing of root, bifid root apex, diversion of canal, narrowing of canal, and interruption of white line [8],[9]. It is a common consensus that OPG provides limited information. The buccolingual relationship between the inferior alveolar canal and the third molar cannot be evaluated [10]. It has limited accuracy in determining the number of roots and root morphology. Conventional computed tomography (CT) has also been used to verify the relationship between the third molar root apices and the mandibular canal [11],[12],[13],[14]. The drawbacks of CT are higher radiation dose and increased financial costs [12],[13],[14],[15].

Cone beam computed tomography (CBCT) has recently been introduced as a valuable diagnostic method [6],[16]. It has been suggested for examination of the mandibular third molars as it provides detailed information about the position and course of the mandibular canal [6],[16]. Compared to conventional CT, CBCT presents short scanning time and radiation dose up to 15 times lower [17]. In this study assessment of Roods and Shehab criteria was done with CBCT to assess the reliability of the signs if one sign is present and if more than one sign is present and course of the IAN was evaluated in relation to the root apex of third molar.


  Materials and Methods Top


Selection

This prospective radiographic study was conducted in Department of Oral and Maxillofacial Surgery during the year 2011–2012. Patients with close relationship between the IAN and mandibular third molars root apex, diagnosed from their panoramic radiographs were included in the study (Roods and Shehab criteria). This included a total of 25 patients of which 16 were males and nine were females. The study was approved by Ethics Committee of the institute and written informed consent was obtained from all the patients. Signs of close relationship included in this study were: darkening of root, deflection of root, narrowing of root, dark and bifid apex of root, interruption of white line of canal, diversion of canal, narrowing of canal.

Evaluation of panoramic images

Digital OPG radiographs were evaluated. The presence or absence of the following radiographic signs was evaluated according to the criteria established by Rood and Shehab: (a) darkening of root, (b) deflection of root, (c) narrowing of root, (d) dark and bifid root, (e) interruption of white line of canal, (f) diversion of canal, (g) narrowing of canal [9].

Presence of single [Figure 1] or two radiographic signs was also evaluated [Figure 2].
Figure 1: Cropped OPG showing only one sign: darkening of root.

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Figure 2: Cropped OPG showing 2 signs: darkening of root and narrowing of canal.

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CBCT scan was done using Planmeca Romexis device (Planmeca System, Helsinki, Finland) operated at 90 kV, 10 mA and exposure time of 15 s. Acquired images were evaluated with a slice width of 400 μm in sagittal sections to determine cortical layer integrity of the mandibular canal in relation to the root apex of third molar. The position of the canal was also assessed whether placed buccal, lingual, between the roots, or inferiorly at the point of closest contact with the third molar root apex along with presence or absence of cortication in the mandibular canal.

Contact

Direct relation between the IAN and third molar apex without any intervening bone [Figure 3].
Figure 3: Sagittal view in CBCT with contact between root apex of third molar and IANC.

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No contact

Presence of bone between IAN and third molar root apex [Figure 4].
Figure 4: Sagittal view in CBCT with no contact between root apex of third molar and IANC.

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Buccal, lingual, between the roots and inferior: the position of the IAN with respect to the third molar root apex at the point of nearest contact [Figure 5] and [Figure 6].
Figure 5: Schematic diagram showing position of third molar root apex and IANC (L=Lingual, B=Buccal), (From left to right, Buccal, Inferior, Lingual and Between the roots placed IANC in respect to third molar root apex).

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Figure 6: Sagittal Cropped images of CBCT showing position of third molar root apices and IANC (From left to right, Buccal, Inferior, Between the roots and Lingual placed IANC in respect to third molar root apex).

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Two investigators evaluated the OPG images and CBCT and a common conclusion was made with discussion.


  Results Top


A total of 47 mandibular third molars were assessed according to Roods and Shehab criteria. Single radiographic sign was seen in 81% of the cases and two or more signs were present in 19% of the cases. The most commonly seen signs were darkening of root followed by interruption of white line of canal and deflection of root.

[Table 1] shows the distribution of the signs according to Roods and Shehab criteria and its assessment with CBCT. Overall in 63.8% of the cases there was disruption of cortical integrity.
Table 1: Assessment of orthopantomogram findings with cone beam computed tomography

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The position of the IAN when assessed using CBCT in relation to root apex of third molar was found buccal in 61.7% of the cases followed by inferior in 23.4% of the cases ([Table 2]).
Table 2: Position of the nerve in respect to third molar root apex

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  Discussion Top


Injury to IAN is uncommon. But the risk may increase from 19 to 30% when there is direct contact between the root and the nerve [18],[19]. Many factors have been suggested as predisposing to IAN injury including age, more deeply impacted teeth, less-experienced surgeons and use of burs to remove bone. Therefore to protect the nerve from mechanical damage during surgery and to clearly assess the relative positions of the nerve and the third molar root tip preoperatively, it is important to evaluate the topographic relationship between the mandibular canal and impacted third molar teeth. This helps in decision making, guiding the treatment plan and informing the patient about the likelihood of nerve damage during removal.

OPG is commonly used to evaluate third molars for impaction surgeries. Numerous clinical studies on basis of OPG have suggested various signs of risk factors for nerve injury. According to those studies the following panoramic features were reported to indicate a close relationship between the third molar root and IAN: darkening of the root, interruption of the canal wall, diversion of the canal, narrowing of the root, deflected root, narrowing of the canal, and dark and bifid root. Rood et al. [9] reported that three panoramic signs which are significantly related to nerve injury are diversion of inferior alveolar canal; darkening of the root, interruption of white line and further two clinically important signs were narrowing of root and deflection of the canal. Similarly Blaeser et al. [20] reported that diversion of canal, darkening of third molar root, and interruption of the cortical white line were associated with IAN injury and absence of these radiographic findings had a strong negative (>99%) predictive value. Monaco et al. [17] reported that increased radiolucency (darker zone where the anatomy of both the root and the mandibular canal are less defined), narrowing and interruption of the radiopaque border of the canal, as well as the concomitant presence of two or more radiographic markers on the panoramic radiograph were highly predictive of contact between the third molar and the mandibular canal. According to Sedaghatfar et al. [21] darkening of the tooth root, narrowing of the tooth root, interruption of the white lines of the mandibular canal, and diversion of the canal were associated with increased IAN exposure following third molar extraction. De Melo Albert et al. [15] evaluated the orthopantomograph for signs of close relationship between the mandibular third molar and IAN: darkening of the roots, island-shaped apex, narrowing of the mandibular canal, reflection of the apexes, narrowing of the root apexes, dark and bifid root apexes, and deviation of the mandibular canal. The most common relationship criterion of potential damage was darkening of the roots (45.2%). A true relationship was confirmed on the tomograph in 92.1% of these cases. Forty seven, third molar teeth were included in this study, darkening of root and interruption of white line was most commonly seen as a single sign. In 19% of the cases more than one radiographic sign was present.

A positive radiographic sign on OPG may indicate a true relationship between the nerve and the root but such a statement cannot be considered very reliable. These signs have poor diagnostic accuracy because impacted third molars are frequently outside the center of rotation of the detector and radiologic source leading to incorrect visualization. Bell et al. [10] reported that only 51% cases had intimate relation between the nerve and the tooth when darkening and only 11% when interruption of white line was present. Other studies have also pointed out limitations of OPG [2],[15]. Similarly Park et al. [22] pointed out that main drawback of panoramic radiography is limited three-dimensional visualization of the positional relationship between the IAN and mandibular third molars. Conventional CT has also been used to evaluate third molar and IAN with drawbacks. Resolution in CT depends on slice thickness and hence requires a high radiation dose. Other minor disadvantages included were such as increased cost, space, and lack of standard parameters for predicting the likelihood of nerve exposure [23]. Maegawa et al. [24] correlated CT findings with surgical results and concluded that medical CT is not very accurate in predicting nerve exposure.

Diagnostic radiology has undergone changes in the last 10 years. Development of hardware and software has allowed applications of new methods for dentomaxillofacial diagnosis and treatment planning. CBCT is an important development in the dental radiology and introduced in oral diagnosis in 1997. The advantages of CBCT-based systems include uniform magnification, a high-contrast image with a well defined image layer free of blurring, multi planar views, three-dimensional reconstructions and the availability of software for image analysis [25]. The displayed reconstructed images can be measured directly on the screen or on a true sized printed copy to determine the anatomical dimensions. CBCT offers several advantages in comparison to conventional CT in depiction of the maxillofacial region, in terms of accuracy, scan time and dose reduction [10],[26]. Dalili et al. [27] pointed that CBCT is a more precise tool to determine the relationship of impacted third molars to the canal. According to Ghaeminia et al. [5] CBCT contributes to better risk assessment and adequate surgical planning as compared with panoramic radiography.

In the present study we used CBCT to evaluate the panoramic findings in cases where the third molar root apices were in close proximity to mandibular canal with high probability of IAN injury. Overall cortical disruption was present in 63.8% of the cases which shows that risk of nerve injury is higher with OPG assessment similar to other previous studies. Cortical integrity of mandibular canal is an important predictor of nerve injury. Studies based on CT and CBCT has shown increased paresthesia in cases with cortical disruption. In our study if two or more signs were present all were associated with disruption of cortical integrity in CBCT images. Similar findings were also reported by Monaco et al. [17] when more than one sign was present in OPG assessed using CT.

The nerve found to be placed more buccally and inferiorly. These findings were similar to findings of Maegawa et al. [24] and Miller et al. [28] but they had used CT for evaluation. Position of mandibular canal in respect to the apex of the third molar has significant clinical importance as pointed by Ghaeminia et al. [6]. It plays a very important role in removal of buccal bone, tooth sectioning, and placement of elevator and direction of tooth removal. Some studies have also revealed that the nerve may be positioned inferiorly, than buccally or lingually. These findings show that only three-dimensional examination can accurately determine the nerve root relation and a better treatment planning. The present study shows that three-dimensional examination in form of CBCT is recommended in cases OPG showing two or more radiological signs.


  Conclusion Top


The results of this study show that CBCT has advantages of visualizing the exact topographic relationship of the mandibular canal to the tooth structure. This helps in planning the surgical procedure and will allow planned guttering of the bone and odontotomy to facilitate tooth removal without causing pressure damage or transection of the IAN. We also strongly recommend CBCT for all cases showing two or more signs in OPG radiographs.

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], [Figure 5], [Figure 6]
 
 
    Tables

  [Table 1], [Table 2]



 

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