1. Evaluation of the Proximity between the Mandibular Third Molar and the Mandibular Canal Using Panoramic and CT Images Joung JI 1, Park SH 1, Choi BR 1, Huh KH 2, Yi WJ 3, Choi SC 2 Though partial overlaps between mandibular third molars and mandibular canals are detected in panoramic radiograph, there may be many cases of encroachment of the canal. Therefore, to define a more accurate relationship between the two, we require CBCT or CT images. The results of this study may lead to guidelines for oral surgeons evaluating whether to obtain an axial CT scan for further investigation. Table 1. Relationship between the root of lower third molar and mandibular canal in panoramic view Table 2. Relationship between the root of lower third molar and mandibular canal in CT images Table 3. Relationship between the root of lower third molar and mandibular canal according to the mandibular canal position Fig 1. Classification of the relationship between the root of lower third molar and mandibular canal in panoramic radiograph. Fig 2. Classification of the relationship between the root of lower third molar and mandibular canal in CT image type point contact superimposit ion partial overlap interruption of upper border diversion of the MC narrowing of the MC case531151742895 %13.829.945.37.32.31.3 no contact between inner and outer wall blurred inner wall narrowing of the MC encroaching the MC total point contact27 (50.9)17 (32.1)4 (7.5)2 (3.8)3 (5.7)53 superimposition10 (8.7)16 (13.9) 57 (49.6)16 (13.9)115 partial overlap31 (17.8)32 (18.4)31 (17.8)41 (23.6)39 (22.4)174 interruption of upper border 1 (3.6)8 (28.6)9 (32.1)3 (23.6)7 (25)28 diversion of the MC001 (11.1)3 (33.3)5 (55.6)9 narrowing of the MC 002 (40) 1 (20)5 total69 (18.0)73 (19.0)63 (16.4)108 (28.1)71 (18.5)384 no contact between inner and outer wall blurred inner wall narrowing of the MC encroaching the MC total buccal39 (32.0)31 (25.4)20 (16.4)16 (13.1) 122 lingual02 (2.3)8 (9.1)59 (67.0)19 (25.7)88 inferior21 (18.3)31 (27.0)24 (20.9)15 (13.0)24 (20.8)115 between the roots 005 (29.4)8 (47.1)4 (23.5)17 total60 (17.5)64 (18.7)57 (16.7)98 (28.7)63 (18.4)342 1) point contact with canal 2) superimposition 3) partially overlapped 4) interruption of the border 5) diversion of mandibular canal 6) narrowing of mandibular canal 1) no contact 2) between inner wall and outer wall of mandibular canal 3) blurred inner wall 4) narrowing of the mandibular canal 5) encroaching the mandibular canal * MC: mandibular canal, ( ): % Introduction The extraction of an impacted mandibular third molar can cause neurological complications due to the damage in the inferior alveolar nerve. It is known that the risk increases markedly when there is direct contact between the nerve and the tooth root. Panoramic radiographs are the most commonly used for assessing the relationship between these two structures preoperatively. But it is restrictively useful for predicting the physical contact. The panoramic [Orthopantomograph op100 (Instrumentarium Corp., Tuusula, Finland)] and CT [Somatom Sensation 10 (Siemens AG, Forchheim, Germany) ] images of 385 impacted mandibular third molar which were obtained from 235 patients (male: 113, female: 125, average age: 28.6) were evaluated. The proximity between the root and the mandibular canal were classified as follows; 1) point contact, 2) superimposition, 3) partial overlap, 4) interruption of upper border, 5) diversion of mandibular canal, 6) narrowing of mandibular canal. The actual relationship between the two structures was assessed using CT images. Also the location of the mandibular canal relative to the mandibular third molar was investigated. In the case of roots' being superimposed on the mandibular canal in panoramic radiograph, 49.6% and 13.9% of the samples exhibited narrowing and encroachment of the canal in CT image respectively. On the other hand, when roots were partially overlapped with the mandibular canal, 23.6% and 22.4% of the samples exhibited narrowing and encroachment of the canal respectively. Considering the position of mandibular canal, 35.7% of the samples were buccal, 25.7% were lingual and 33.6% were inferior. When the position of the mandibular canal was lingual, narrowing of the canal appeared much more frequently than in other cases (67.0%). * MC: mandibular canal, ( ): % 1 Department of Oral and Maxillofacial Radiology, School of Dentistry, Seoul National University, Seoul, South Korea, 2 Department of Oral and Maxillofacial Radiology, Dental Research Institute, School of Dentistry, Seoul National University, Seoul, South Korea, 3 Department of Oral and Maxillofacial Radiology, Dental Research Institute and BK21, School of Dentistry, Seoul National University, Seoul, South Korea. The purpose of this study was to evaluate the diagnostic accuracy of panoramic radiograph in assessing the proximity between the root of mandibular third molar and the mandibular canal. Objective Materials & Method Results Conclusion & discussion