Bull Tokyo Dent Coll (2015) 56(1): 1–8
Original Article
Characteristic Findings on Panoramic Radiography and Cone-beam CT to Predict Paresthesia after Extraction of Impacted Third Molar Nana Harada1), Beloor Vasudeva Subash1), Yukiko Matsuda1), Kenji Seki1), Rishabh Kapila1), Noboru Ishikawa2), Tomohiro Okano1) and Tsukasa Sano1) Division of Radiology, Department of Oral Diagnostic Sciences, Showa University School of Dentistry, 2-1-1 Kitasenzoku, Ota-ku, Tokyo 145-8515, Japan 2) Department of Forensic Anthropology, Tokyo Dental College, 2-9-7 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-0062, Japan 1)
Received 31 January, 2014/Accepted for publication 25 August, 2014
Abstract The purpose of this study was to compare findings on the relationship between impacted molar roots and the mandibular canal in panoramic and three-dimensional cone-beam CT (CBCT) images to identify those that indicated risk of postoperative paresthesia. The relationship between impacted molars and the mandibular canal was first classified using panoramic images. Only patients in whom the molar roots were either in contact with or superimposed on the canal were evaluated using CBCT. Of 466 patients examined using both panoramic and CBCT images, 280 underwent surgical extraction of an impacted molar, and 15 of these (5%) reported postoperative paresthesia. The spatial relationship between the impacted third molar root and the mandibular canal was determined by examining para-sagittal sections (lingual, buccal, inter-radicular, inferior, and combinations) obtained from the canal to the molar root and establishing the proximity of the canal to the molar root (in contact with or without loss of the cortical border and separate). The results revealed that darkening of the roots with interruption of the mandibular canal on panoramic radiographs and the inter-radicular position of the canal in CBCT images were characteristic findings indicative of risk of postoperative paresthesia. These results suggest that careful surgical intervention is required in patients with the above characteristics. Key words:
Impacted third molar — Paresthesia — Inferior alveolar nerve — Panoramic radiography — Cone-beam CT
Introduction
third molars if postoperative complications, including paresthesia, are to be avoided. This information will include the distance from the root apex to the mandibular canal; the
There is certain important information that the dentist requires in dealing with impacted 1
2
Harada N et al.
inclination of the tooth root(s) to the buccal or lingual cortical plate; and the course of the mandibular canal in relation to the roots2). Preoperative radiographic assessment of impacted third molars helps the surgeon to obtain this information. Panoramic radiographs provide information on impaction status, any associated pathologies, and the relationship of the impacted third molar to the adjacent tooth. They also provide clues about the relationship of the third molar to the mandibular canal. Using panoramic radiographs, Rood and Shehab identified seven radiographic signs that indicate a close relationship between the third molar root and the mandibular canal and its distance from the buccal or lingual cortical plate9). Three-dimensional information is also useful in clarifying the relationship of the third molar to the mandibular canal. Such information is not available with panoramic images, however. Cone-beam CT (CBCT) is extensively employed by dentists to obtain three-dimensional information, and this imaging modality has been reported to have several advantages over panoramic radiography5,6,12). The following guideline was recommended: “Where conventional radiographs suggested a direct inter-relationship between a mandibular third molar and the mandibular canal, and the decision to perform surgical removal has been made, CBCT may be indicated”4). In routine practice, however, many oral surgeons still evaluate the status of impacted third molars based on panoramic images alone. Information obtained from correlative studies of panoramic and three-dimensional images obtained using CBCT could help surgeons interpret panoramic images from a three- dimensional perspective. The relationships among panoramic radiographic signs, the incidence of neurovascular bundle exposure, and inferior alveolar nerve injury have been studied, and the results suggest that one or more panoramic findings, including darkening of the third molar root, interruption of the cortical white line, narrowing of the tooth root, and diversion of the canal, are
associated with an increased risk of nerve injury1,3,11). Therefore, the aim of this study was to compare findings on the relationship between impacted molar roots and the mandibular canal in panoramic and three-dimensional CBCT images to identify those indicative of risk of postoperative paresthesia.
Materials and Methods The patients included in this study were referred to the Radiology Department at Showa University Dental Hospital, Tokyo, Japan, for surgical extraction of impacted third molars. All underwent preoperative panoramic radiography to determine the spatial relationship between the impacted tooth and the mandibular canal. The panoramic images obtained were then analyzed and only patients in whom the roots were either in contact with or superimposed on the canal were further referred for CBCT. Informed consent was obtained from all patients for inclusion in the study. A total of 466 patients, including 203 men and 263 women with a mean age of 36.0 years (range, 17 to 82 years) underwent both panoramic radiography and CBCT. Panoramic images were acquired using the Hyper-XF (Asahi Roentgen Company Ltd., Kyoto, Japan), with exposure at 78 kV and 10 mA and the patient positioned according to the manufacturer’s instructions. The CBCT images were acquired using the 3D Accuitomo ( J. Morita, Kyoto, Japan), with exposure at 90 kV and 4 mA and a cylindrical field of view with a height of 4 cm and diameter of 4 cm. The relationship between the third molar root and the mandibular canal in the panoramic radiographs was classified as follows using the criteria reported by Rood and Shehab9): darkening of the root (Type A); deflection of the root (Type B); narrowing of the root (Type C); dark or bifid root (Type D); interruption of the mandibular canal white line (Type E); diversion of the mandibular canal (Type F); or narrowing of the mandibular canal (Type
3
Panoramic Signs to Predict Paresthesia
Table 1 Distribution of impacted third molar and mandibular canal results of panoramic radiography 1-A
1-B Patients Patients Patients with with nowith paresthesia paresthesia extraction
Panoramic findings on impacted molar and mandibular canal (Rood and Shehab 1990)
Patients examined
Patients with extraction
Type A: Darkening of root
171 (.37)
94 (.34)
8
10
18
Type B: Deflection of root
7 (.02)
3 (.01)
7*
255
262
Type C: Narrowing of root
2 (.00)
2 (.01)
15
265
280
Type D: Dark/Bifid apex of root
6 (.01)
3 (.01)
Type E: Interruption of cortical border of canal
226 (.48)
144 (.51)
Type F: Diversion canal
10 (.02)
6 (.02)
Type G: Narrowing canal
20 (.04)
10 (.04)
Type A/E: Darkening and interruption
24 (.05)
18 (.06)
Total
466 (1)
280 (1)
Significant difference in distribution, p
Original Article
Characteristic Findings on Panoramic Radiography and Cone-beam CT to Predict Paresthesia after Extraction of Impacted Third Molar Nana Harada1), Beloor Vasudeva Subash1), Yukiko Matsuda1), Kenji Seki1), Rishabh Kapila1), Noboru Ishikawa2), Tomohiro Okano1) and Tsukasa Sano1) Division of Radiology, Department of Oral Diagnostic Sciences, Showa University School of Dentistry, 2-1-1 Kitasenzoku, Ota-ku, Tokyo 145-8515, Japan 2) Department of Forensic Anthropology, Tokyo Dental College, 2-9-7 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-0062, Japan 1)
Received 31 January, 2014/Accepted for publication 25 August, 2014
Abstract The purpose of this study was to compare findings on the relationship between impacted molar roots and the mandibular canal in panoramic and three-dimensional cone-beam CT (CBCT) images to identify those that indicated risk of postoperative paresthesia. The relationship between impacted molars and the mandibular canal was first classified using panoramic images. Only patients in whom the molar roots were either in contact with or superimposed on the canal were evaluated using CBCT. Of 466 patients examined using both panoramic and CBCT images, 280 underwent surgical extraction of an impacted molar, and 15 of these (5%) reported postoperative paresthesia. The spatial relationship between the impacted third molar root and the mandibular canal was determined by examining para-sagittal sections (lingual, buccal, inter-radicular, inferior, and combinations) obtained from the canal to the molar root and establishing the proximity of the canal to the molar root (in contact with or without loss of the cortical border and separate). The results revealed that darkening of the roots with interruption of the mandibular canal on panoramic radiographs and the inter-radicular position of the canal in CBCT images were characteristic findings indicative of risk of postoperative paresthesia. These results suggest that careful surgical intervention is required in patients with the above characteristics. Key words:
Impacted third molar — Paresthesia — Inferior alveolar nerve — Panoramic radiography — Cone-beam CT
Introduction
third molars if postoperative complications, including paresthesia, are to be avoided. This information will include the distance from the root apex to the mandibular canal; the
There is certain important information that the dentist requires in dealing with impacted 1
2
Harada N et al.
inclination of the tooth root(s) to the buccal or lingual cortical plate; and the course of the mandibular canal in relation to the roots2). Preoperative radiographic assessment of impacted third molars helps the surgeon to obtain this information. Panoramic radiographs provide information on impaction status, any associated pathologies, and the relationship of the impacted third molar to the adjacent tooth. They also provide clues about the relationship of the third molar to the mandibular canal. Using panoramic radiographs, Rood and Shehab identified seven radiographic signs that indicate a close relationship between the third molar root and the mandibular canal and its distance from the buccal or lingual cortical plate9). Three-dimensional information is also useful in clarifying the relationship of the third molar to the mandibular canal. Such information is not available with panoramic images, however. Cone-beam CT (CBCT) is extensively employed by dentists to obtain three-dimensional information, and this imaging modality has been reported to have several advantages over panoramic radiography5,6,12). The following guideline was recommended: “Where conventional radiographs suggested a direct inter-relationship between a mandibular third molar and the mandibular canal, and the decision to perform surgical removal has been made, CBCT may be indicated”4). In routine practice, however, many oral surgeons still evaluate the status of impacted third molars based on panoramic images alone. Information obtained from correlative studies of panoramic and three-dimensional images obtained using CBCT could help surgeons interpret panoramic images from a three- dimensional perspective. The relationships among panoramic radiographic signs, the incidence of neurovascular bundle exposure, and inferior alveolar nerve injury have been studied, and the results suggest that one or more panoramic findings, including darkening of the third molar root, interruption of the cortical white line, narrowing of the tooth root, and diversion of the canal, are
associated with an increased risk of nerve injury1,3,11). Therefore, the aim of this study was to compare findings on the relationship between impacted molar roots and the mandibular canal in panoramic and three-dimensional CBCT images to identify those indicative of risk of postoperative paresthesia.
Materials and Methods The patients included in this study were referred to the Radiology Department at Showa University Dental Hospital, Tokyo, Japan, for surgical extraction of impacted third molars. All underwent preoperative panoramic radiography to determine the spatial relationship between the impacted tooth and the mandibular canal. The panoramic images obtained were then analyzed and only patients in whom the roots were either in contact with or superimposed on the canal were further referred for CBCT. Informed consent was obtained from all patients for inclusion in the study. A total of 466 patients, including 203 men and 263 women with a mean age of 36.0 years (range, 17 to 82 years) underwent both panoramic radiography and CBCT. Panoramic images were acquired using the Hyper-XF (Asahi Roentgen Company Ltd., Kyoto, Japan), with exposure at 78 kV and 10 mA and the patient positioned according to the manufacturer’s instructions. The CBCT images were acquired using the 3D Accuitomo ( J. Morita, Kyoto, Japan), with exposure at 90 kV and 4 mA and a cylindrical field of view with a height of 4 cm and diameter of 4 cm. The relationship between the third molar root and the mandibular canal in the panoramic radiographs was classified as follows using the criteria reported by Rood and Shehab9): darkening of the root (Type A); deflection of the root (Type B); narrowing of the root (Type C); dark or bifid root (Type D); interruption of the mandibular canal white line (Type E); diversion of the mandibular canal (Type F); or narrowing of the mandibular canal (Type
3
Panoramic Signs to Predict Paresthesia
Table 1 Distribution of impacted third molar and mandibular canal results of panoramic radiography 1-A
1-B Patients Patients Patients with with nowith paresthesia paresthesia extraction
Panoramic findings on impacted molar and mandibular canal (Rood and Shehab 1990)
Patients examined
Patients with extraction
Type A: Darkening of root
171 (.37)
94 (.34)
8
10
18
Type B: Deflection of root
7 (.02)
3 (.01)
7*
255
262
Type C: Narrowing of root
2 (.00)
2 (.01)
15
265
280
Type D: Dark/Bifid apex of root
6 (.01)
3 (.01)
Type E: Interruption of cortical border of canal
226 (.48)
144 (.51)
Type F: Diversion canal
10 (.02)
6 (.02)
Type G: Narrowing canal
20 (.04)
10 (.04)
Type A/E: Darkening and interruption
24 (.05)
18 (.06)
Total
466 (1)
280 (1)
Significant difference in distribution, p
