J. Lumbini. Med. Coll. Vol 8, No 1, Jan-June 2020 Licensed under CC BY 4.0 International License which permits use, distribution and reproduction in any medium, provided the original work is properly cited. ___________________________________________________________________________________ Submitted: 22 April, 2020 Accepted: 25 May, 2020 Published: 15 June, 2020 a- Lecturer, Department of Oral Medicine and Radiology, b- Associate Professor, Department of Oral and Maxillofacial Surgery, c- Assistant Professor, Department of Periodontology and Oral Implantology, d- Lecturer, Department of Community Dentistry, e- Lecturer, Department of Conservative Dentistry and Endodontics, f- Associate Professor, Department of Prosthodontics, g-Dhulikhel Hospital, KUSMS, Nepal h-Universal College of Medical Sciences-College of Dental Surgery, Bhairhawa, Nepal. i-B.P. Koirala Institute of Health Sciences, Dharan, Nepal. Corresponding Author: Harleen Bali e-mail: harleenbali.hb@gmail.com ORCID: https://orcid.org/0000-0001-8647-9582 _______________________________________________________ ABSTRACT Introduction: Third molar extractions are one of the most common reasons of injury to mandibular nerve and post-operative complications. Pre-operative assessment of pending doom is a must. In order to study the relations between change in Inferior Alveolar Canal (IAC) and Type, Class, and Level of impaction with radiographic root change of impacted third mandibular molar, we designed a study to assess the relationship of the mandibular canal to the roots of impacted third molar in reference to changes in roots and factors affecting it. Methods: This was a retrospective cross-sectional study where in the panoramic radiographic records of subjects with impacted third molar were assessed for change in root and its correlation with change in IAC, Type, Class and Level of impacted mandibular third molar. Results: Roots of impacted third molar when in contact with IAC presented most often in our study subjects with the Darkening of roots in both sides {right side (16.79%) and left side (11.29%)} and both genders {males (right-14.29%, left-8.75%) and females (right-19.39%, left-13.94%)}. They were statistically significantly associated with interruption of white line of IAC, vertically impacted third molars and Pell and Gregory Class II, Level A of impaction. Conclusion: There is a need to properly identify radiographic risk predictor signs to avoid any surprises at the time of extraction and post-operative complications following it. Keywords: Impacted tooth, Mandibular nerve, Panoramic radiography Original Research Articlehttps://doi.org/10.22502/jlmc.v8i1.303 Harleen Bali,a,g Deepak Yadav,b,h Khushbu Adhikari,c,i Swagat Kumar Mahanta,d,g Rupam Tripathi,e,h Binam Sapkota f,g The Relationship of The Mandibular Canal to The Roots of Impacted Third Molars- The Root Factor: A Panoramic Radiographic Study. How to cite this article:How to cite this article: Bali H, Yadav D, Adhikari K, Mahanta SK, Tripathi R, Sapkota B. The Relationship of the Mandibular Canal to the Roots of Impacted Third Molars- The Root factor: A Panoramic Radiographic Study. Journal of Lumbini Medical College. 2020;8(1):8 pages DOI: https:// doi.org/10.22502/jlmc.v8i1.303 Epub: 2020 June 15. INTRODUCTION: Impacted teeth have been associated with pathologies such as cysts, tumors, infections, inflammations of jaws as well as displacement and resorption of adjacent teeth. The mandibular third molars are among the most frequent to be impacted.[1] Their extraction can cause direct injury to Inferior Alveolar Nerve (IAN) or hematoma formation following extraction putting pressure over the nerve leading to neurosensory disturbances.[2,3] Studies have reported that the prevalence of IAN paraesthesia following third molar surgery ranges approximately from 0.4% to 8.4%.[4] In order to avoid such untoward incidents pre-operative investigations are required to plan the protocol best suiting the scenario. Among 2D imaging, surgeons prefer panoramic radiographs than intraoral periapical radiographs for planning third molar extraction. Though 3D imaging modalities promise clearer picture, their reduced accessibility and high cost have restricted their use J. Lumbini. Med. Coll. Vol 8, No 1, Jan-June 2020 Bali H et al. The Relationship of the Mandibular Canal to the Roots of Impacted Third Molars- The Root factor: A Panoramic Radiographic Study. jlmc.edu.np in developing countries. Studies are available on prevalence of root changes[5] seen in mandibular third molar when in contact with Inferior Alveolar Canal (IAC) but the relation of change in root with factors like change in IAC, type, level and class of impaction is less explored and none so in Nepal to the best of our knowledge. Therefore, the aim of our study was to assess the root changes seen in mandibular third molar when in contact with IAC and factors affecting it. METHODS: This descriptive cross-sectional study was conducted in Universal College of Medical Sciences- College of Dental Surgery, Bhairahawa. The radiographic records of patients with impacted third molar were selected in a retrospective manner. The records from January 2016 were selected as starting point and all preoperative orthopentomograms (OPGs) till February 2018 were selected for the present study. Ethical clearance was obtained from the Institutional Ethical Committee prior to conducting the study. More than 2000 panoramic radiographs were scanned, of which 673 were included in this study. All radiographs had been taken using Vatech digital X-ray system, model: PCH-2500 (power input: AC 100-120/200-240 V, 50/60 Hz, 2.0 kVA Max. 170 VA Normal; output- 90 kV, 10 mA and Focal Spot 0.5x0.5 mm). All OPGs were shot at 73kVp, 10.0mA and scan time13.5 seconds in standard mode. The inclusion criterion was individuals’ OPG presenting with bilateral impacted mandibular third molars with root completion and presence of mandibular second molars. The exclusion criteria were individuals with: (1) trauma/surgery to the mandibular site of study, (2) developmental anomalies affecting the jaws, and (3) radiographic evidence of pathologies of the impacted mandibular third molar teeth of mandible which could obscure the visualization of the periapical region or IAC. The radiographs were observed and read by an oral and maxillofacial surgeon, well trained and experienced in reading radiographs. The type of impaction of mandibular third molars was identified by the method adapted by Winter.[6] Subsequently, they were categorized as mesioangular, distoangular, vertical or horizontal impactions. The Pell–Gregory classification[7] in relation to ramus of the mandible (Class I, II and III) and Pell–Gregory classification[7] in relation to depth/level of mandibular third molar in relation to occlusal surface of second molar (A, B and C) was also identified and recorded. Digital panoramic radiographs were then interpreted cautiously for the following: The presence of each of the following sign in root of mandibular third molar and Inferior Alveolar Canal changes (Rood and Shehab).[5] Changes in root: a. Darkening of the root: Loss of root density in a tooth that is impinged upon by the canal. b. Deflection of the root: An abrupt deviation of roots near the canal. c. Dark and bifid root apex: A loss of root density in a tooth that is impinged upon by the canal with bifid apex of the root. d. Narrowing of the root: Narrowing of the tooth roots where the canal crosses. Changes in IAC: a. Interruption of the white line: Discontinuity of the superior radio-opaque line that constitutes the superior border of the inferior alveolar canal. b. Diversion of the canal: A change in the direction of the canal while crossing the mandibular third molar. c. Narrowing of the canal: An abrupt decrease in the width of the canal while it crosses the root apices. Data was entered in MS Excel sheet and analyzed using Statistical Package for Social Sciences (SPSSTM) software version 20. Statistical analysis was done to evaluate the change in roots of impacted third molar caused by contact/superimposition of IAC a. with respect to right or left side of mandible b. with respect to gender c. Its relation to the Type of impaction, Pell– J. Lumbini. Med. Coll. Vol 8, No 1, Jan-June 2020 Bali H et al. The Relationship of the Mandibular Canal to the Roots of Impacted Third Molars- The Root factor: A Panoramic Radiographic Study. jlmc.edu.np Gregory Class and Level of Impaction of mandibular third molar. Descriptive statistics and Chi-Square, post hoc test was done. P value <0.01 was considered significant. RESULTS: The tabulated results were analyzed. Of the selected 673 radiographs, 330 (49.03%) were of females and 343 (50.96%) were of males. The age group ranged from 21 to 65 years (Mean+ SD=31.63+11.98). Radiographic risk predictor signs in roots of impacted mandibular third molar were seen in 176 (26.15%) subjects on the right side and 133(19.76%) on the left side (Figure 1). Fig. 1. Overall change in roots in our study. Roots of impacted third molar when in contact with IAC presented most often in our study subjects with the darkening of roots in both sides {figure1-right side (16.79%) and left side (11.29%)} and both genders {table 1: Males (right-14.29%, left- 8.75%) and Females (right-19.39%, left-13.94%)}. Darkening along with other changes was also seen and grouped under others. Change in roots of impacted third molar when correlated with changes noticed in IAC, showed interruption of white line (table 2a: right side-55.90%, left side-56.98%) as the most common effect. The results were statistically highly significant (p<0.001). Post hoc test after chi square was done to know which group was statistically significant among them. It showed that interruption of white line (right and left side of mandible), while diversion of IAC on left side were statistically highly significant (see table 2b). An analysis of Winter’s Classification of Type of impaction correlation with darkening of roots revealed vertical impaction (Table 3: right side-62.99%, left side-52.33%), followed by mesioangular impaction (right side-27.56%, left side- 36.05%). The results were statistically significant (p<0.01) on right side and statistically highly significant (p<0.001) on left side. Pell and Gregory Category for depth/Level of mandibular third molar impaction when correlated with the change in roots i.e. Darkening of roots showed position A (Table 4: right side-58.27%, left side-47.67%) followed by position B (right side-26.77%, left side- 30.23%) as most related. Fig. 2. No. of roots of mandibular third molar with respect to right and left side. Pell and Gregory Class defining space Table 1. Change in root of mandibular third molar as per gender. Change in root Male (Frequency, %) Female (Frequency, %) Right Left Right Left No Change 266 (77.55%) 288(83.97%) 231 (70.00%) 252 (76.36%) Darkening of Root 49 (14.29%) 30 (8.75%) 64 (19.39%) 46 (13.94%) Deflected 17 (4.96%) 19 (5.54%) 20 (6.06%) 23 (6.97%) Dark and Bifid 1 (0.29%) 1 (0.29%) 2 (0.61%) 0 (0.0%) Narrowing of Roots 2 (0.58%) 1 (0.29%) 7 (2.12%) 3 (0.91%) Others 8 (2.33%) 4 (1.16%) 6 (1.82%) 6 (1.82%) Total 343 343 330 330 J. Lumbini. Med. Coll. Vol 8, No 1, Jan-June 2020 Bali H et al. The Relationship of the Mandibular Canal to the Roots of Impacted Third Molars- The Root factor: A Panoramic Radiographic Study. jlmc.edu.np Table 2a. Darkening of roots of mandibular third molar on right and left side of mandible with respect to change in IAC seen on the same side. Change in IAC Right Left No Change 41 (32.28%) X2 (6,127)= 165.116, p value < 0.001* 21 (24.42%) X2(6, 86)=134.185, p value < 0.001*Interruption of white line 71 (55.90%) 49 (56.98%) Diversion of IAC 5 (3.94%) 6 (6.98%) Narrowing of IAC 5 (3.94%) 5 (5.81%) Others 5 (3.94%) 5 (5.81%) Total 127 86 Table 2b. Darkening of roots of mandibular third molar on right and left side of mandible with respect to change in IAC seen on the same side. Change in IAC p-value Right side Left side Right side Left side No Change 41 21 <0.001 < 0.001 Interruption of white line 71 49 <0.001 <0.001 Diversion of IAC 5 6 .10358 .00065 Narrowing of IAC 5 5 .2096 .5407 Others 5 5 .011 <0.001 Table 3: Darkening of roots in respect to Winter’s Classification of type of impaction of mandibular third molar. Winter’s Classification Right Left Mesioangular 35 (27.56%) X2(3, 127)=13.490, p value < 0.01* 31 (36.05%) X2 (4,86)=24.347, p value< 0.001*Distoangular 5 (3.94%) 5 (5.81%) Vertical 80 (62.99%) 45 (52.33%) Horizontal 7 (5.51%) 5 (5.81%) Total 127 86 Table 4: Darkening of roots in respect to Pell and Gregory Depth/Level of Impaction of mandibular third molar. Pell and Gregory Level of Impaction Right Left A 74 (58.27%) X2 (3, 127)=27.426 p value <0.001* 41 (47.67%) X2 (3,86)=46.638 p value <0.001*B 34 (26.77%) 26 (30.23%) C 19 (14.96%) 19 (22.1%) Total 127 86 Table 5: Darkening of roots in respect to Pell and Gregory Class of Impaction of mandibular third molar. Pell and Gregory Class of Impaction Right Left I 52 (40.94%) X2 (3, 127)=33.175, p value <0.001* 27 (31.4%) X2 (3, 86)=38.6 p value <0.001*II 61 (48.03%) 48 (55.81%) III 14 (11.02%) 11 (12.79%) Total 127 86 * denotes satistitically significant. J. Lumbini. Med. Coll. Vol 8, No 1, Jan-June 2020 Bali H et al. The Relationship of the Mandibular Canal to the Roots of Impacted Third Molars- The Root factor: A Panoramic Radiographic Study. jlmc.edu.np available between the anterior border of the ascending ramus and the distal aspect of the second molar when correlated with the Darkening of roots showed class II (Table 5: right side-48.03%, left side-55.81%) followed by class I (right side-40.94%, left side- 31.4%) as most related. The results were statistically highly significant (p<0.001). DISCUSSION: One of the complications of extraction of impacted mandibular third molars is dysaesthesia due to injury to the IAN either directly or following hematoma formation. Rood and Shebab[5] studied and recognized various radiographic risk predictor signs. With the coming of new and advanced 3 D imaging modalities, investigations for pre-operative decision making have become an indispensable tool. Still panoramic radiographs hold their own significance when coming to pre-operative investigation for impacted tooth extraction as they are easily accessible and more affordable for the patients in developing countries. Males constituted more than females in our study sample in accordance with Gupta et al.,[8] and Deshpande.[1] In contrast, studies by Jerjes,[3] Knutsson et al.,[9] and Szalma et al.,[10] observed a female preponderance. Previous studies on panoramic radiograph reported that the darkening of the third molar root was strongly suggestive of an intimate relationship between the root and nerve, or nerve injury following third molar extraction.[4,5,11,12,13,14,15,16,17,18] Our study showed that darkening of roots was most common phenomenon (with respect to gender and right and left side; table 1 and graph 1) noted on panoramic radiograph under change in roots of mandibular third molars when in contact/ superimposed by IAC and that it was associated with interruption of white line of IAC in majority of cases (Table 2). This could be attributed to the researches reporting that darkening or dark band across the roots when in contact with the IAC is due to loss of dentine caused by grooving of the root by the canal[14,19,20] or that darkening of the root may indicate thinning of the cortical plate rather than grooving of the root as observed by Mahasantipiya et al.[21] Our study findings were in accordance with Peker et al.,[22] who reported a significant correlation between darkening of the roots and interruption of the white line on panoramic radiography and the presence of contact on Cone Beam Computed Tomography (CBCT) images. Study by Neves et al.,[23] also concluded that darkening of roots and interruption of white line observed on panoramic radiographs, both as isolated findings and in association, were effective in determining the risk relationship between the tooth roots and the IAC. Our study reported that darkening of roots was most frequently associated with vertical impactions, followed by mesioangular impactions among our subjects (Table 3). This was in contrast with Miloro and DaBell[24] who reported that mesioangular impactions followed by vertical impactions were closer to the inferior alveolar canal. Deshpande et al.,[1] also reported mesioangular impactions to be associated with radiographic risk predictor signs followed by horizontal impactions, but stated it to be statistically insignificant similar to study concluded by Blaeser et al.[25] Monaco G et al.,[12], Hashemipour MA et al.[26] and Obiechina AE et al.[27] reported that the level of impaction assessed based on the Pell and Gregory classification showed that Level A of impaction was the most common when considering both upper and lower third molars. In our study Level A of impaction for mandibular third molars was most associated with darkening of roots (Table 4). Haung et al.,[28] in their study found that majority of impacted mandibular third molars were in Pell and Gregory Class II. Our results showed impaction was in Class II in majority cases in respect to darkening of roots (Table 5). Our study was limited to the use of panoramic radiograph whereas more sophisticated imaging modalities such as CBCT are available today. Panoramic radiograph can be used as preliminary investigation to assess the relationship of IAC and mandibular third molars. If it shows proximity between the two structures further investigations using 3 D imaging, though expensive and not as accessible as panoramic, should be considered. Though this was a panoramic study, meta- analysis by Atieh in 2010,[29] done to determine the diagnostic accuracy of panoramic radiographic markers in detecting the relationship between J. Lumbini. Med. Coll. Vol 8, No 1, Jan-June 2020 Bali H et al. The Relationship of the Mandibular Canal to the Roots of Impacted Third Molars- The Root factor: A Panoramic Radiographic Study. jlmc.edu.np impacted mandibular third molar roots and the inferior alveolar canal suggested a reasonable diagnostic accuracy for panoramic radiography for the same. CONCLUSION: Our study showed darkening of root as the most common radiographic risk predictor sign seen on panoramic radiographs when change in roots of mandibular third molar was studied. They were statistically significantly associated with interruption of white line of IAC, vertically impacted third molars and Pell and Gregory Class II, Level A of impaction. We conclude that there is a need to properly identify radiographic risk predictor signs to avoid any surprises at the time of extraction and post operation complications following it. Conflict of interest: The authors declare that no competing interests exist. Financial disclosure: No funds were available for the study. J. Lumbini. Med. 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