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Authors : Dr. Suraj Agarwal.

ABSTRACT

BACKGROUND AND OBJECTIVE: To pre-evaluate position of Inferior alveolar nerve to impacted mandibular third molar on Digital OPG & CBCT.

METHODS: Sample consisted of 34 individuals with 43 impacted mandibular third molars who underwent pre-operative radiographic evaluation before extraction of impacted mandibular third molars. Individuals who showed close proximity of impacted mandibular third molars to inferior alveolar canal underwent CBCT. On CBCT, cortical integrity, canal calibre, position of nerve, in relation to impacted mandibular third molars were evaluated.

RESULTS: Darkening of root, Interruption of white line of canal, Narrowing of canal & Diversion of canal were associated with the canal compression, absence of corticalization between the mandibular third molar and mandibular canal on CBCT images. Also significant difference(p<0.05) was found between digital OPG & CBCT for evaluation of position of impacted mandibular third molar, number of roots and presence/absence of dilacerations of roots.

CONCLUSION: Darkening of roots, interruption of white line of canal & narrowing of canal observed on panoramic radiographs, both as isolated findings and in association, were effective in determining the risk relationship between the tooth roots & the mandibular canal, requiring three dimensional evaluation of cases.

KEYWORDS: Cone Beam Computed Tomography, Inferior Alveolar Nerve, Mandibular Third Molar, Panoramic Radiography, Radiological signs. Manuscript

ACKNOWLEDGEMENT

I would like to thank Dr. Achint Garg, Head of Department, Oral Medicine & Radiology, ITS Dental College, Hospital & Research Centre, Greater Noida, Dr. Upasana Sethi Ahuja, Reader, Oral Medicine & Radiology, ITS Dental College, Hospital & Research Centre, Greater Noida, Dr. Siddharth Gupta, Reader, Oral Medicine & Radiology, ITS Dental College, Hospital & Research Centre, Greater Noida & Dr. Samta Goel Mittal, Senior Lecturer, Oral Medicine & Radiology, ITS Dental College, Hospital & Research Centre, Greater Noida for helping me to carry out this research work.

INTRODUCTION

Extraction of third molars is a routine procedure in maxillofacial surgery, whether for prophylactic or for orthodontic reasons. Usually there is little risk to adjacent structures, although in some cases there may be complications owing to the intimate relationship between the roots of the third molars and the mandibular canal and/or the mandibular lingual cortex. Third molars have a high incidence of impaction associated with many conditions such as pericoronitis, caries on the distal surface of the second molar, pain, external root resorption and odontogenic cysts or tumors. Difficulties in the eruption of the third molars, particularly in the mandible, are attributed to a lack of space caused by late formation and the phylogeny of the mandible.1,2

The inferior alveolar nerve runs in a canal within the mandible near the apices of the lower third molar. During surgical removal of mandibular third molar, the inferior alveolar nerve is damaged occasionally.3 Damage to the inferior alveolar nerve manifests itself as a sensory disturbance of the lower lip & chin upto the midline. It is therefore important to predict & assess the risk of nerve damage.4

The reported incidence of the inferior alveolar nerve injury after the surgical removal of impacted mandibular third molar (IMTM) ranges from 0.4% to 8.4%.5 Clinically, neurosensory disorders related to inferior alveolar nerve (IAN) can be manifested as pain, anesthesia, paresthesia, or a combination of these conditions.6

An imaging exam is undoubtedly an essential tool for diagnosis and surgical management because it provides valuable information about the tooth position, the number/morphology of the roots and, especially, the relationship of the tooth to adjacent structures. The panoramic radiograph is routinely used as an auxiliary examination for treatment planning of lower third molar removal, due to its wide availability, low cost and relatively low exposure doses.2

Studies suggest that seven specific signs observed on panoramic radiograph (darkening of roots; deflection of roots; narrowing of roots; bifid root apex; diversion of canal; narrowing of canal; interruption in the white line of the canal) are reliable ways to assess the relationship between the third molar and the mandibular canal.7,8 Rood and Shebab9 and others have suggested that 3 of the 7 signs more significantly associated with inferior alveolar nerve injury are:

1) Darkening of the root, which has previously been explained by a reduction of bulk of root substance due to the inferior alveolar canal or nerve grooving the root9, 2)Interruption of the white line of the inferior alveolar canal, which has been attributed to the deep grooving or perforation of the root or a loss of the cortical margin of the canal so the root is in contact with the nerve,103) Diversion of the inferior alveolar canal, which has been interpreted as indicating that the canal had perforated the root and ‘been dragged’ upwards during subsequent tooth eruption, or the root during development has displaced the nerve so that a change in directionappears.11

Another traditionally accepted criteria for estimations of difficulty and risk during lower third molar removal is the evaluation of the impacted tooth according to the classification of Pell & Gregory (PG) and Winter (Figure 1 & 2).12PG classification distributes impacted molars in three categories according to their vertical positioning (related to the occlusal and cervical plane of adjacent molars)and three horizontal categories (related to the mandibular ascending ramus). Winter classification is divided in four categories based on tilting of the impacted molar in relation to its longitudinal axis.
 
FIGURE 1: PELL-GREGORY CLASSIFICATION FOR IMPACTED MANDIBULAR THIRD MOLAR FIGURE 2: ANGULATION OF IMPACTED MANDIBULAR THIRD MOLAR BY WINTER’S CLASSIFICATION 1) MESIOANGULAR 2) DISTOANGULAR 3) VERTICAL 4) HORIZONTAL 5) BUCCOANGULAR 6) LINGUOANGULAR 7) INVERTED.


Assessment of the buccolingual direction is very important for cases in which the IMTM and the IAC are in closeproximity.13,14 Since, panoramic radiography is a Two Dimensional (2D) imaging modality it provides limited information about buccolingual relationship between the mandibular canal & mandibular third molar, cortication of the mandibular canal and desired anatomy of the third molar.

Three-dimensional (3D) imaging with conventional computed tomography and cone-beam computed tomography (CBCT) is recommended in these cases to detect the exact relationship.13 Cone beam CT (CBCT) is a radiographic method that has been used in several areas of dentistry because it shows three-dimensional (3D) images of dental structures in addition to providing clear structural images with high contrast. It is being used increasingly in many dental specialties, including orthodontics,15 orthognathic surgery,16 and implant dentistry.17

Increasingly, CBCT is replacing medical CT because it provides adequate image quality associated with a lower exposure dose. Other advantages of CBCT are the low cost of the examination compared with computed tomography (CT), fast scanning time, lower number of artefacts and real-time image analysis.18,19 Tantanapornkul et al20 concluded that CBCT was significantly superior to panoramic images in predicting neurovascular bundle exposure during extraction of impacted mandibular third molar.

Although CBCT allows such evaluation, panoramic radiography is still often the first imaging method requested for the investigation of third molars.2 Moreover, ALARA Principle should be a concern among professionals, seeking to extract maximum information from an imaging modality, avoiding further exposure.21 Thus the aim of the study was, Pre-Operative Radiographic Evaluation of Inferior Alveolar Nerve, Radiographic Sign & Position of Impacted Mandibular Third Molar on Digital OPG & CBCT.

Materials & Methodology

Materials used were, Diagnostic instruments (Probe, Mouth mirror, Tweezer), Digital panoramic radiographs will be taken with PlanmecaRomexisProline XC 2.1.0.R, Cone Beam Computed Tomography images are assessed through KODAK dental imaging software 3dv2.2 (kdis). Inclusion Criteria for the study was, Individuals between 2nd to 4th decade of life, Clinically, mandibular third molar should be partially erupted or should not be visible in the oral cavity &Patient willing to undergo further radiographic evaluation by Cone Beam Computed Tomography.

Exclusion Criteria included, Patient not willing for further radiographic evaluation by Cone Beam Computed Tomography, Patients who are having any systemic disease causing change in bone morphology such as diabetes mellitus, uncontrolled hypertension, hyperthyroidism, multiple sclerosis etc. or change in canal course such as neurofibromatosis, hemangioma etc. , Patient with radiological evidence of a cyst or tumor or any other lesion, Radiographic absence of tooth bud of mandibular third molar &Pregnant patients.

Methodology, this study was a cross sectional study conducted between the period from November 2012 - July 2014. 34 patients who reported to the Department of Oral Medicine & Radiology in I.T.S –Dental College Hospital & Research Centre, Greater Noida aged between 2nd and 4th decade were included in the study. Clinical examination regarding position of impacted mandibular third molars was done (partially erupted or absent) with a record of demographic details like patient’s age, sex and after examination, patient was advised digital OPG.

A close relationship with the inferior alveolar canal were evaluated on DIGITAL OPG, according to the radiographic signs i.e. Darkening of the roots, Island – shaped apex, Narrowing of the mandibular canal, Deflection of the apexes, Narrowing of the apexes, Dark and bifid apexes, Deviation of the mandibular canal.

Images were evaluated by using PlanmecaRomexis Software and cases with impacted third molar with a sign of close relationship to mandibular canal was then subjected to Cone Beam Computed Tomography (CBCT) with slice thickness of 1mm and field of view 5x5cm. The images were obtained in axial, sagittal and coronal planes to determine the true relationship. Demographic data was maintained (containing information on the patient’s gender and age), DIGITAL OPG findings & CBCT radiological findings was evaluated for each case.

All the patients were informed with regard to the purpose of the study and effects of radiation. After the consent of patient and case history, relative findings were recorded using a pre-structured performa.

RESULTS

34 patients who reported to the Department of Oral Medicine and Radiology, I.T.S Dental College Hospital and Research Centre, Greater Noida participated in this study. 34 patients (P= number of patients) with 43 impacted mandibular third (N= number of teeth) molars showed 50 radiographic signs of proximity of mandibular third molar to inferior alveolar nerve on Digital Panoramic Radiographs for which Cone Beam Computed Tomography was done.

DEMOGRAPHIC DATA

The age of the patients involved in the study ranged from 20-40 years. Number of patients in age range 20-25 years – 19 (55.8% of cases), 26-30 years – 7 (20.5% of cases ), 31-35 years - 5 (14.7% of cases ), 36-40 years - 3 (8.8% of cases ). The mean age was 27.7 years. Of the 34 patients 27 were male and 7 female patients. Of the 43 impacted teeth in 34 patients, 24 teeth (55.8%) are on right side and 19 teeth (44.1%) are on left side. Total number of bilaterally impacted teeth were 9(20.9%). (Table1) On clinical examination, 13 teeth were partially erupted and 30 teeth were completely embedded. 15 patients presented with pain, 8 patients presented with pericoronitis with partially erupted or completely embedded third molars.
 
TABLE 1: AGE ,SEX AND SIDE OF IMPACTION OF IMPACTED THIRD MOLARS DISTRIBUTION AMONG PATIENTS DISTRIBUTION OF PATIENTS.


DIGITAL ORTHOPANTOMOGRAM FINDINGS

Of the 43 impacted teeth, position of impacted teeth according to Pell-Gregory classification: class I were seen in 3 patients (6.9%), class II were seen in 34 patients (79%), class III were seen in 6 patients (13.9%). Depth of impacted teeth according to Pell-Gregory Classification: Depth B were seen in 10 patients (23.2%), Depth C were seen in 33 patients (76.7%), Depth A impacted teeth were not found in the study. Of the 43 impacted teeth, Angulation of impacted teeth according to Winter’s classification: horizontal impactions were seen in 13 (30.2%) cases, vertical impactions in 4 (9.3%), mesioangular impactions in 26 (60.4%) cases and distoangular impactions in 1(2.3%). (Table 2)
 
TABLE 2: POSITION, DEPTH AND ANGULATION OF IMPACTED MANDIBULAR THIRD MOLARS ON DIGITAL OPG.


Of the 43 impacted teeth, radiographic sign of proximity of mandibular third molar to inferior alveolar nerve, in 28 teeth (65.11%) darkening of root were seen, in 13 teeth interruption of white line of canal was seen (30.2%), in 6 teeth (11.6%) narrowing of canal was seen and in 1 teeth (2.3%) diversion of canal was seen.(Table 3, Graph 1)
 
TABLE 3: DISTRIBUTION OF SIGNS PRESENT ON N=43 TEETH EXAMINED
 
GRAPH 1: RADIOLOGICAL SIGNS OF PROXIMITY OF MANDIBULAR THIRD MOLAR TO IAN


CONE BEAM COMPUTED TOMOGRAPHY FINDINGS

Relation to inferior alveolar nerve - cortical plate thinning/resorption on CBCT, buccal cortical plate in 2 teeth (4.65%), lingual cortical plate in 36 teeth (83.7%), both in 1 teeth (2.3%) and intact in 4 teeth (9.3%). Relation to inferior alveolar nerve – canal calibre on CBCT, intact in 26 teeth (60.4%) and reduced or compressed in 17 teeth (39.5%). Relation to inferior alveolar nerve – position of inferior alveolar nerve on CBCT, buccal in 14 teeth (32.5%), lingual in 12 teeth (27.9%) and inferior or inter-radicular in 17 teeth (39.5%). Out of 43 impacted teeth, only 1 teeth showed bifid inferior alveolar canal or accessory inferior alveolar canal branch. (Table 4, Figure 7)
 
TABLE 4: RELATION TO INFERIOR ALVEOLAR CANAL- CORTICAL INTEGRITY, CANAL CALIBRE, CANAL POSITION & ACCESSORY IAN BRANCH


ON EVALUATION OF DIGITAL OPG AND CBCT FINDINGS

On digital OPG, Darkening of root was seen in 30 teeth. Out of these 30 teeth, 1 teeth (3.3%) showed thinning of cortical plate of buccal aspect, 26 teeth (86.6%) showed thinning of lingual aspect and 3 teeth (10%) showed intact cortical plate. Out of these 30 teeth, 14 teeth (46.6%) showed reduced canal calibre and 16 teeth (53.3%) showed intact canal calibre. Out of these 30 teeth, 12 teeth (40%) showed inferior alveolar nerve canal on buccal aspect, 6 teeth (20%) on lingual aspect and 12 teeth (40%) inferior or inter-radicular region.(Table 5).
 
TABLE 5: CORRELATION OF OPG AND CBCT FINDINGS: DARKENING OF ROOTS


On digital OPG, Interruption of white line of canal was seen in 13 teeth. Out of these 13 teeth, 2 teeth (15.3%) showed thinning of cortical plate of buccal aspect, 9 teeth (69.2%) showed thinning of lingual aspect, both in 1 teeth (7.69%) and 1 teeth (7.69%) showed intact cortical plate. Out of these 13 teeth, 5 teeth (38.46%) showed reduced canal calibre and 8 teeth (61.5%) showed intact canal calibre. Out of these 13 teeth, 1 teeth (7.69%) showed inferior alveolar nerve canal on buccal aspect, 6 teeth (46.1%) on lingual aspect and 6 teeth (46.1%) inferior or inter-radicular region. (Table 6)
 
TABLE 6: CORRELATION OF OPG AND CBCT FINDINGS- INTERRUPTION OF WHITE LINE OF CANAL


Narrowing of canal was seen in 6 teeth. Out of these 6 teeth, 1 teeth (16.6%) showed thinning of cortical plate of buccal aspect, 4 teeth (66.6%) showed thinning of lingual aspect and both in 1 teeth (16.6%). Out of these 6 teeth, 4 teeth (66.6%) showed reduced canal calibre and 2 teeth (33.3%) showed intact canal calibre. Out of these 6 teeth, 1 teeth (16.6%) showed inferior alveolar nerve canal on buccal aspect, 2 teeth (33.3%) on lingual aspect and 2 teeth (33.3%) inferior or inter-radicular region. (Table 7)
 
TABLE 7: CORRELATION OF OPG AND CBCT FINDINGS- NARROWING OF CANAL


Diversion of canal was seen in 1 teeth, with thinning of lingual cortex, reduced canal calibre and position of nerve/canal lingually. (Table 8)
 
TABLE 8: CORRELATION OF OPG AND CBCT FINDINGS: DIVERSION OF CANAL


DISCUSSION

Accurate pre-operative prediction of neurovascular bundle position is very useful while extracting impacted mandibular third molars, for warning patients of the potential risk of post-operative dysesthesia and obtaining informed consent. Radiological assessment is essential in evaluating the topographic relationship between the mandibular canal and the impacted third molar, and panoramic images are most commonly used for this purpose.

Although panoramic images cannot provide three dimensional information, numerous clinical studies have been performed to determine panoramic signs suggestive of intraoperative neurovascular bundle exposure or post-operative dysesthesia. Various radiographic signs on panoramic radiographs, which suggest a close relationship of mandibular third molar to mandibular canal are: darkening of root, interruption of the canal wall, diversion of canal, narrowing of root, deflected root, narrowing of canal, and dark and bifid root. Renton et al22 (2005) described a ‘new’radiological feature: the juxta-apical area and suggested that it was predictive of an increased risk of nerve injury.

Rood and Shehabet al7 (1990) analysed panoramic images of 1560 mandibular third molars and reported that the first 3 features were significantly correlated with the occurrence of post-operative dysesthesia. Rud11(1983) and Kipp et al23 (1980) also reported similar finding. Sedaghatfar et al24 (2005) reported a retrospective study showing that the first 4 features were significantly associated with inferior alveolar nerve exposure at extraction and that the sensitivity and specificity of these features ranged from 42% to 75% and 66% to 91%, respectively.

However they did not determine the optimal diagnostic criteria for panoramic images in predicting exposure. Bell et al25 (2003) reported that the sensitivity and specificity of panoramic images in prediciting exposure were 66% and 74% on average respectively. They also reported that these values varied widely among observers and emphasized the need for further standardization of diagnostic criteria.

Due to the recent development and acceptance of CBCT, three dimensional images are becoming more easily available in dentistry. CBCT is proving to be increasingly beneficial in determining the precise relationship between these two structures in those individuals where the panoramic radiographs suggests the relationship to be close. The CBCT images can be reformatted with minimal distortion allowing the canal and tooth to be viewed in all dimensions.

Its use results in patients receiving a greater radiation dose compared to standard radiography; therefore it is not appropriate for CBCT to be used as the first routine imaging technique and should be applied when the benefits of the additional exposure are likely to be considerable. Hashimoto et al26 (2003) has reported that CBCT is significantly superior to conventional CT. The CBCT appearance of the mandibular canal usually is a well defined radiolucent zone, lined by radiopaque borders.

The radiographic density of this lucent structure is variable, with the presence of a radiopaque outline being dependent on the canal’s cortication. As a result, in few young patients, the mandibular canal is not well visualized. Carter27 (1970) had earlier reported that radiologically invisible IAN canal may occur because the IAN bundles are not always surrounded by an ossified canal. Stella28 (1990) had previously reported of the reliability and accuracy of conventional tomography as part of the preimplant evaluation of posterior mandibular sites to the visibility of the IAN canal.

The present study was designed to correlate digital panoramic radiographic findings with CBCT to determine the proximity of mandibular third molar to inferior alveolar nerve and to predict precise anatomical relationship of third molar to IAN in all the dimension.

Several studies have demonstrated, the presence of two or more signs on a panoramic radiograph indicates an increased risk of IAN exposure29,30,31,32 or injury.8 In the present study, darkening of roots, interruption in white line, narrowing of canal and diversion of canal have been associated with the absence of corticalization between the mandibular third molar and the mandibular canal in CBCT images were statistically significant, as both isolated findings and in association with each other.

In the study by Gomes et al33 (2008) , no statistically significant association was observed between the presence of the seven panoramic radiographic signs and IAN paraesthesia after third molar extractions. However, Ghaeminiaet al34 (2009) observed that three panoramic radiographic signs (interruption of white line, darkening of roots and diversion of the mandibular canal) were significantly associated with IAN exposure.

Clinical studies have demonstrated that the absence of corticalization between the tooth roots and the mandibular canal on spiral CT images and IAN exposure are significantly associated only with some panoramic radiographic signs—in particular, darkening of roots and interruption of white line.29Szalma et al35 (2009) identified three signs on panoramic radiograph that were significantly associated with IAN paraesthesia (interruption of white line, diversion of the mandibular canal and darkening of roots). Monaco et al36 (2004) determined the reliability of panoramic radiograph in evaluating the relationship between the mandibular canal and the roots of the third molar based on multidetector CT images.

According to the authors, the 3D exam should be carried out when darkening of roots, narrowing of the mandibular canal and interruption of white line are observed on panoramic radiograph. FS Neves et al37 (2012) found that the narrowing of the mandibular canal was not associated with higher risk of contact between the tooth roots and the mandibular canal, either as an isolated finding or in association with other panoramic radiographic signs, based on CBCT images.

In our results we found that darkening of root, interruption of white line of canal, narrowing of canal and diversion of canal are associated with higher risk of contact between the tooth roots and the mandibular canal both on digital OPG and CBCT. In our study of panoramic findings, darkening of roots had the highest frequency (69.5%), interruption of white line of canal (30.2%), narrowing of canal (13.9%) while deviation of canal had the lowest (2.1%).(Figure 3) These findings are according to the observations of Monaco et al36 (2004) and Tantanapornkul et al20 (2007). In these studies, panoramic signs of the darkening of the roots and the interruption of the radiopaque border of the canal were the most frequent, while panoramic signs of the deviation of the canal and narrowing of the canal were the least frequent, respectively.

Tooth contact with the cortex was observed in 90.6% of the impacted molars (39 teeth) evaluated. (Figure 4) This contact with the lingual cortex was found in 83.7% of the third molars and concurs with the result of the Ohmanet al38 (2006) study (86%).Surgeons awareness of the thinning or perforation of the cortex may decrease the risk of lingual nerve injury or displacement of bone or tooth fragments to the adjacent structure. Surgeon’s knowledge about the location of the IAN is of paramonut importance in the preoperative evaluation of impacted third molars to guide the elevator and luxate the involved tooth. IAN injuries commonly occur during third molar removal because of compression and traction on the nerve through movements of the tooth roots.9

IAN injury may occur during elevation of mesioangular impacted third molars because the roots may move apically and may compress the nerve.39 Also, movements of the third molar root in the buccolingual direction can cause compression of the IAN. The surgical approach is generally initiated from the buccal side of the impacted third molar in cases in which the surgeon lacks information about the buccolingual course of the IAN before surgery. However, the IAN may experience undesirable forces if it is positioned lingually and IAN injury has been reported in such cases.

CBCT images allow the clinician to perform comprehensive treatment planning and surgical method selection during preoperative assessment.39Ghaeminia et al39 (2011), Mahasantipiya et al40 (2005), Ohman et al38 (2006) have reported that the IAC is most frequently positioned on the lingual side of impacted third molars and the contact between the IAC and the impacted teeth was generally observed in these cases. In the present study, the IAC was most frequently located on the inferior/inter-radicular (39.5%), followed by (32.5%) and lingual (27.9%) of the IMTM and they were commonly in contact/compressed/canal calibre reduced(41.8%). (Figure 5)
 
FIGURE 3: RADIOGRAPHIC SIGN OBSERVED ON DIGITAL OPG : A – NARROWING OF CANAL, B – DIVERSION OF CANAL, C – DARKENING OF ROOT, D – INTERRUPTION OF WHITE LINE OF CANAL


Surgeons must know the type and/or angle of the impacted third molar before surgery to prevent perforation and fracture of the mandible, and to select appropriate operation procedures.41 Previous studies have classified the IMTM as vertical, horizontal or angular, based on its orientation to the mandible.42Tantanapornkul et al20 (2007) reported that the horizontal type was the most frequent (52%), followed by angular (32%) and vertical (16%). Momin et al42 (2013) reported similar results, with 42% horizontal, 37% angular and 21% vertical.
 
FIGURE 4: CORTICAL PLATE RESORPTION OBSERVED ON CBCT: A – BUCCAL, B – LINGUAL, C - INTACT FIGURE 5: POSITION OF INFERIOR ALVEOLAR CANAL ON CBCT: A – BUCCAL, B – INFERIOR/INTERRADICULAR, C - LINGUAL


Msagati et al43 (2013) and Syed et al44 (2013) found that the mesioangular type was the most common (76% in Msagati’s study and 50.75% in Syed’s study). Lubbers et al15 (2011) reported that mesially angulated (40.2%) and vertical (29%) were the most common types. In the present study, the most frequent type was found to be mesioangular (60.4%), then horizontal (30.2%), followed by vertical (9.3%). This finding was in agreement with the results of Lubbers et al15 (2011). Differences between studies may arise because of different study samples. (Figure 6)

Various types of bifid mandibular canals have been described and classified in the literature according to anatomical location and configuration, by using panoramic radiographs.45However, few studies have used computerized tomography for this purpose.46,47According to Rouas et al,47(2007) panoramic radiographs can only suggest the presence of bifid mandibular canals, but cannot confirm them. According to the authors, only a tridimensional image exam, such as the cone beam computed tomography (CBCT), can show the presence and morphology of the bifurcation path of the mandibular canal precisely. In present study, 1 teeth with accessory IAC branch was found which was not precisely visible on DPR but CBCT revealed accessory IAN branch which was retromolar to 48. (Figure 7)
 
FIGURE 6:ANGULATION OF IMPACTED MANDIBULAR THIRD MOLAR ON DIGITAL OPG A – MESIOANGULAR, B – HORIZONTAL, C- VERTICAL FIGURE 7: ACCESSORY INFERIOR ALVEOLAR NERVE BRANCH OBSERVED ON CBCT


CONCLUSION

CBCT has significantly improved our understanding of the relationship between mandibular third molars and the inferior alveolar canal previously described by panoramic radiography. We have demonstrated that darkening of the root correlates to thinning of lingual cortical plate, Interruption of white lines of canal indicates that the canal and hence its contents are in contact with tooth.

Narrowing of the canal correlates to the course of the nerve being altered as it contacts and passes the roots due to space restriction in the mandible. Of the predictive signs observed on panoramic radiographs, darkening of root, interruption of white line of canal, narrowing of canal are highly suggestive of nerve/root contact. All three signs reflect a risk relationship between tooth and nerve which is confirmed by CBCT.

Planning the surgical removal of lower third molars can be effectively and precisely enhanced with the use of CBCT, which provides not only an accurate understanding of the position of the nerve in relation to the third molar, thereby facilitating a risk reducing surgical approach or treatment, but also other potential complication, for example, risk of herniation of tooth fragments into the lingual fossa when the lingual cortical plate, is thinned substantially.

Thus, preoperative surgical predictability and understanding of the anatomy depicting the relationship between impacted mandibular third molar and associated structures can be enhanced using CBCT. A larger sample sized longitudinal studies are required to prescribe CBCT as benchmark for third molar surgical extractions.

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More References Are Available On Request

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