tomography depicting mandibular neurovascular canal structures
Munetaka Naitoh, DDS, PhD,aKino Nakahara, DDS,bYutaka Suenaga, DDS,b Kenichi Gotoh, RT,cShintaro Kondo, DDS, PhD,dand Eiichiro Ariji, DDS, PhD,e Nagoya, Japan
AICHI-GAKUIN UNIVERSITY
Objective. The most common diagnostic imaging modalities for cross-sectional imaging in dental implant planning are currently cone-beam computed tomography (CBCT) and multislice CT (MSCT). However, clinical differences between CBCT and MSCT in this task have not been fully clarified. In this investigation, the detection of fine anatomical structures in the mandible was assessed and compared between CBCT and MSCT images.
Study design. The sample consisted of 28 patients who had undergone CBCT and MSCT. The bifid mandibular canal in the mandibular ramus, accessory mental and buccal foramina, and median and lateral lingual bony canals were observed in 2-D images, and the findings were compared between CBCT and MSCT.
Results. Four of 19 canals observed in CBCT were not observed in MSCT images. Three accessory mental foramina in 2 patients and 28 lateral lingual bony canals in 18 patients were observed consistently using the two methods.
Conclusion. Depiction of fine anatomic features in the mandible associated with neurovascular structures is consistent between CBCT and MSCT images. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2010;109:e25-e31)
The most common diagnostic imaging modalities for cross-sectional imaging in dental implant planning are currently cone-beam computed tomography (CBCT) and multislice CT (MSCT).1-6 The normal anatomic structures in the oral and maxillofacial region and cer- vical soft tissue have been compared using CBCT and MSCT images.7-10Hashimoto et al.7reported that the image quality of CBCT images using the 3DX unit (J.
MORITA Mfg. Corp., Kyoto, Japan) was better than that of MSCT images for all of the following: cortical bone, cancellous bone, enamel, dentin, the pulp cavity, lamina dura, and periodontal ligament space. Misch- kowski et al.9and Dreiseidler et al.10reported that the mandibular foramen, mandibular canal, mental fora- men, and incisive foramen could be observed and the
diagnostic quality was the same between CBCT and MSCT.
The location and course of various neurovascular bony canals, such as the bifid mandibular canal, acces- sory mental and buccal foramina, and median and lat- eral lingual bony canals in the mandible, are important for dental implant fixture insertion and implant-related bone grafting.11-17 However, the relative detection of these anatomic structures has not been fully clarified.
Therefore, the purpose of this study was to compare the detection of fine mandibular structures, such as the bifid mandibular canal, accessory mental and buccal foramina, and median and lateral lingual bony canals, was assessed and compared between CBCT and MSCT images.
MATERIALS AND METHODS Subjects
Since April 2007 CBCT has been performed for diagnostic imaging in dental implant planning, instead of MSCT, in our hospital. Twenty-eight (6 males and 22 females) of 342 patients undergoing CBCT imaging up until March 2009 were previously imaged using MSCT imaging. All patients were sufficiently informed regarding MSCT and CBCT, and gave their informed consent to participate. The reason for CBCT imaging was to assess bone grafting in 5 patients, for additional implant fixture insertion in 11 patients, and for the follow-up observation of inserted fixtures in 12 pa-
aAssociate Professor, Department of Oral and Maxillofacial Radiol- ogy, School of Dentistry, Aichi-Gakuin University, Nagoya, Japan.
bGraduate student, Department of Oral and Maxillofacial Radiology, School of Dentistry, Aichi-Gakuin University, Nagoya, Japan.
cRadiologic Technician, Division of Radiology, Dental Hospital, Aichi-Gakuin University, Nagoya, Japan.
dAssociate Professor, Department of Anatomy, School of Dentistry, Aichi-Gakuin University, Nagoya, Japan.
eProfessor and Chairman, Department of Oral and Maxillofacial Radiology, School of Dentistry, Aichi-Gakuin University, Nagoya, Japan.
Received for publication Jun 5, 2009; returned for revision Jul 17, 2009; accepted for publication Aug 14, 2009.
1079-2104/$ - see front matter
© 2010 Published by Mosby, Inc.
doi:10.1016/j.tripleo.2009.08.027
e25
tients. The mean age was 54.5 years (range: 21-74, SD ⫾10.9) at the time of CBCT imaging. The mean time between MSCT and CBCT imaging was 30.1 months (range: 6.7-58.8, SD⫾15.0).
Imaging
The Alphard VEGA (Asahi Roentgen, Kyoto, Japan) CBCT unit with a flat-panel detector was used. The exposure volume was set at 102 mm in diameter and 102 mm in height (I-mode), and the voxel size was 0.2⫻ 0.2 ⫻ 0.2 mm. The scan was set at 80 kV and 5 mA, as recommended by the manufacturer. The DICOM files of the axial images were saved to a portable hard disk (HD).
MSCT imaging was performed using a HiSpeed NX/i Pro (GE Yokogawa Medical Systems, Tokyo, Japan) unit. The helical scan was set at 120 kV, 200 mA, with 0.5-mm-thick slices, and a 1.5 table pitch.
The axial images were reconstructed using 0.5-mm- thick slices with 0.25-mm intervals, and the field of view (FOV) in axial images was set at 160 mm in diameter. The pixel size of axial images was 0.31 ⫻ 0.31 mm. A series of axial images in DICOM files were saved on a portable HD.
Observation of mandibular anatomical structures Two oral and maxillofacial radiologists (M.N. and K.N.) reconstructed and interpreted CBCT and MSCT images simultaneously. The presence of bifid mandib- ular canal in the mandibular ramus, accessory mental and buccal foramina, and middle and lateral lingual bony canals was recored in axially, cross-, and longi- tudinally sectioned 2-dimensional (2-D) images using a computer (Macintosh G4, Apple Computer, Cuper- tino, CA) and 3-D visualization software (OsiriX Imaging Software, the OsiriX Foundation, Geneva, Switzerland),18 and the findings were compared be- tween CBCT and MSCT images.
The course and bifurcation of the mandibular canal were assessed, and the length of the bifurcated canal was measured. The presence of a bifid mandibular canal was recorded when the length was 5 mm or greater. When a secondary bifurcation of the bifid canal
was observed, both secondary canals were measured.
Bifid mandibular canals were classified into 4 types:
retromolar, dental, forward, and bucco-lingual canals.11 Because 16 sides that underwent bone block harvests from the retromolar region and 2 sides that underwent sagittal split ramus osteotomy were excluded from bifid mandibular canal assessment, a total of 38 sides were analyzed.
An accessory mental foramen was defined as a buc- cal foramen showing continuity with the mandibular canal, excluding the mental foramen.12 A buccal fora- men was defined as a canal penetrating the buccal cortical bone from the buccal bone surface not showing continuity with the mandibular canal, the so-called nu- trient foramen.13 The 56 sides of the 28 patients were analyzed for their presence.
The superior and inferior genial spinal bony ca- nals,14,15other canals in the median mandible, and the lateral lingual bony canal in the premolar region16,17 were observed in cross-sectional images, and they were analyzed in all 28 patients.
Statistical analysis
The differences between CBCT and MSCT in the depiction of the bifid mandibular canal, accessory men- tal foramen, buccal foramen, median lingual bony ca- nal, and lateral lingual bony canal in the premolar region were evaluated using chi-square statistics. Dif- ferences were considered significant at P less than .01.
RESULTS
A comparison of the visualization of mandibular anatomical structures between CBCT and MSCT im- ages is presented inTable I.
Bifid mandibular canal
In CBCT images, a bifid mandibular canal was ob- served on 18 of 38 sides. A secondary bifurcation was noted on one side, and a total of 19 bifid mandibular canals were observed. A retromolar canal was pre- sented in 3 canals, and a forward canal in 16 canals. In MSCT images, 15 bifid canals including 1 secondary canal were observed on 14 sides. The retromolar canal
was presented in 3 canals, and a forward canal in 12 canals. Thirteen bifid mandibular canals with 3 retro- molar and 10 forward canals were clearly noted in both CBCT and MSCT images. Four forward canals ob- served in CBCT images were not identified in MSCT images (Fig. 1). Moreover, 2 forward bifid canals in an MSCT image were observed to be longer than in a CBCT image (Fig. 2).
Accessory mental foramen
Three accessory mental foramina were clearly ob- served in both CBCT and MSCT images (Fig. 3).
Buccal foramen
Twenty-seven buccal foramina in 1 median region and on 22 sides were observed in CBCT images, and 27 buccal foramina in 1 median region and on 21 sides were noted in MSCT images (Fig. 4). Two buccal foramina were observed in either of the 2 CT images.
Median lingual bony canal
In total, 53 median lingual bony canals in 28 patients were clearly identified in both CBCT and MSCT im- ages (Fig. 5), and only 1 superior genial spinal bony canal was observed in CBCT images. Using CBCT images, a superior genial spinal bony canal was noted in 5 patients; inferior canal in 2 patients; superior and inferior canals in 14 patients; superior and man- dibular inferior border canals in 1 patient; and superior, inferior, and mandibular inferior border canals in 6 patients.
Lateral lingual bony canal in the premolar region A lateral lingual bony canal on 28 sides was ob- served in both CBCT and MSCT images (Fig. 6).
There were no significant differences between CBCT and MSCT regarding the depiction of the bifid man- dibular canal, accessory mental foramen, buccal fora- Fig. 1. Bifid mandibular canal on the left side of a 47-year-old man. A bifid mandibular canal was observed in the CBCT image (A). It courses forward at first and superiorly after the crook. It was not observed in the MSCT image (B), and a metal artifact was superimposed on the retromolar region.
Fig. 2. Bifid mandibular canal on the left side of a 49-year-old woman. The bifid mandibular canal (white arrowhead) observed in the MSCT image (B) was longer than that in the CBCT (A) image.
men, median lingual bony canal, and lateral lingual bony canal in the premolar region.
DISCUSSION
Presently, CBCT and MSCT have been recom- mended as appropriate cross-sectional diagnostic imag- ing modalities for dental implant assessment1-6; how- ever, their use has not been described in the Japanese guidelines for such diagnostic imaging.19The accuracy of CBCT and MSCT images is reportedly high in linear measurement.1,2,4,5Also, Mischkowski et al.9and Dre- iseidler et al.10 reported that various mandibular ana- tomical structures could be observed, and the diagnos- tic quality was the same between CBCT and MSCT
images. Our study confirms the results of these previ- ous authors in that both modalities are equally capable of detecting the presence of fine mandibular structures, such as the bifid mandibular canal, accessory mental and buccal foramina, and median and lateral lingual bony canals. Although the mean time between CBCT and MSCT imaging was approximately 30.1 months, we considered that the mandibular structures did not markedly change during this period.
Within the retromolar canal, which is one type of bifid mandibular canal, the artery branched from the inferior alveolar artery, and nerves derived from the inferior alveolar nerve trunk were observed.20 Also, the retromolar nerves branched off to the buccal mu- Fig. 3. Accessory mental foramen on the left side of a 46-year-old woman. An accessory mental foramen was clearly observed in both CBCT (A) and MSCT (B) images. White arrowhead, accessory mental foramen; black arrowhead, mental foramen.
Fig. 4. Buccal foramen on the left side of a 62-year-old man. A buccal foramen (white arrowhead) was clearly observed in both CBCT (A) and MSCT images (B).
cosa and the buccal gingiva of the mandibular premolar and molar regions in one Japanese cadaver.20 Toh et al.21observed the accessory mental nerve extending to the mucous membrane and the skin of the corner of the mouth, as well as the mucous membrane of the median labial region. Also, the accessory mental nerve com- municated with branches of the facial and buccal nerves. The buccal foramina is considered to be the so-called nutrient foramen.13Ichikawa22reported that a nutrient foramen was formed in a prenatal stage, and the submental, lower lip, and buccal arteries and direct branches of the facial artery distributed from the buccal foramen into mandibular cancellous bone. Jacobs et al.14 reported that the superior genial spinal foramen contained a branch of the lingual artery and vein and
lingual nerve. Also, a branch of the mylohyoid nerve together with branches or anastomoses of the sublin- gual and/or submental artery and vein were identified upon entering the inferior genial spinal foramen. Yo- shida et al.17observed a branch of the inferior alveolar artery in the lateral lingual foramen of the mandibular premolar region. Moreover, it was indicated that poten- tial risks might also be related to the presence of the lingual foramen and anatomic variations, such as an anterior looping of the mental nerve.23
We have previously reported that the presence of the bifid mandibular canal in the mandibular ramus region is more often observed on CBCT images (65%), com- pared with panoramic images (Range: 0.08 to 0.95%).11 Four of 19 bifid canals observed in CBCT images were Fig. 5. Superior and inferior genial spinal bony canals in the median region of a 62-year-old man. Superior (white arrowhead) and inferior (black arrowhead) genial spinal bony canals were clearly observed in both CBCT (A) and MSCT images (B).
Fig. 6. Lateral lingual bony canal in the premolar region of a 49-year-old woman. A lateral lingual bony canal (white arrowhead) was observed in both CBCT (A) and MSCT images (B).
almost identical for CBCT and MSCT images. The long axis of the accessory mental foramen was reported to range from 1.1 to 2.9 mm in CBCT images.12The mean long axis of the accessory mental foramina in CBCT images was 2.7 mm in the study, and it was comparatively large in the accessory mental foramina.
The buccal foramen, reported in 44% of patients by Naitoh et al.,13was observed in 57% of patients using both CBCT and MSCT images. A superior and/or in- ferior genial spinal bony canal was observed in 100%
of patients. Kawai et al.15 reported that a superior or inferior genial spinal bony canal was presented in 97.1% of dry mandibles.
A lateral lingual bony canal was observed on 28 sides (50.0%) in 18 patients (64.3%) using CBCT. In a previous study, it was observed on 43.7% of sides of dry skulls and on 14.8% of sides of cadavers.17These results using CBCT and MSCT were similar to those using dry skulls.
CBCT presents with some major advantages com- pared with MSCT. First, the radiation exposure dose of the patients is relatively low.24,25 Second, the CBCT machine can be used effectively in a dental clinic, but MSCT machine availability is usually limited to hos- pitals. Third, the level of resolution in CBCT images was reportedly higher than that in MSCT images.2In the present investigation, no large differences between CBCT and MSCT images were observed regarding the depiction of fine anatomical structures in the mandible, which included the accessory mental and buccal foram- ina and median and lateral lingual bony canals. How- ever, the additional effectiveness of CBCT images might be shown by observing the bifid mandibular canal in the mandibular ramus region.
The quality of CBCT images may be influenced by the type of x-ray detector (image intensifier versus flat panel), and the diameter of the exposure field. Also, the quality of MSCT images may be influenced by the multidetector, slice thickness, and pixel size. Further studies involving anatomical structures are necessary to compare CBCT and MSCT images in multiple facilities with various CT machines.
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Reprint requests:
Munetaka Naitoh, DDS, PhD
Department of Oral and Maxillofacial Radiology School of Dentistry
Aichi-Gakuin University 2-11, Suemori-Dori, Chikusa-Ku Nagoya 464-8651, Japan mune@dpc.aichi-gakuin.ac.jp
