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Diagnostic imaging with newly developed ortho cubic super-high resolution computed tomography (Ortho-CT) Masaaki Terakado, DDS, PhD,a Koji Hashimoto, DDS, PhD,b Yoshinori Arai, DDS, PhD,c Masahiko Honda, DDS, PhD,d Tadanobu Sekiwa, DDS, PhD,d and Hiroshi Sato, DDS, PhD,e Tokyo, Japan NIHON UNIVERSITY Objective. Ortho cubic super-high resolution computed tomography (Ortho-CT), which we have developed, is characterized by the small size of the unit and the ability to produce 3-dimensional images of high resolution with low-radiation doses. The purpose of this study was to investigate the clinical usefulness of Ortho-CT for the diagnosis of diseases in the oral and maxillofacial region. Study design. Ortho-CT has been used for the imaging diagnosis of a radicular cyst of the upper first molar, mesiodense, tooth fractures in the upper anterior region, a fracture of the condylar process, or presurgical evaluation for a dental implant. The usefulness of 3-dimensional images obtained by Ortho-CT was investigated in this study. Results. Ortho-CT produced images of high resolution, enabling identification of the extent of the lesions and the fracture line, the condition of the impacted tooth, and the relationship with the maxillary sinus, mandibular canal, and adjacent teeth. Conclusion. Because Ortho-CT can take high-resolution 3-dimensional images at any tomographic layer with only 1 exposure, it is useful for the diagnosis of diseases in the oral and maxillofacial region. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2000;89:509-18) Accurate examination of the oral and maxillofacial regions by means of conventional radiography is often difficult because of the complex 3-dimensional anatomic structures in these regions.1,2 Thus, magnetic resonance imaging (MRI) and x-ray computed tomography (CT) are widely used for 3-dimensional imaging diagnosis.3-7 However, because these methods were developed mainly for the diagnosis of diseases involving a larger part of the human body (such as malignant tumors), minute changes of small lesions found in dental diseases are often overlooked by these methods, which have insufficient resolution. Therefore, the techniques are not always effective.8-10 These methods are also unfavorable because the apparatus is large, radiation dose to the patient is high for conventional x-ray CT, and the cost is prohibitive. Therefore, to resolve these problems, the development of ortho cubic super-high resolution CT (Ortho-CT) optimized for dental diseases was started in 1992 in the Department of Radiology at Nihon University School of aAssociate Professor, Department of Oral and Maxillofacial Surgery, School of Dentistry. bAssociate Professor, Department of Radiology, School of Dentistry. cInstructor, Department of Radiology, School of Dentistry. dInstructor, Department of Oral and Maxillofacial Surgery, School of Dentistry. eProfessor and Chairman, Department of Oral and Maxillofacial Surgery, School of Dentistry. Received for publication July 20, 1999; returned for revision Sept 19, 1999; accepted for publication Oct 18, 1999. Copyright © 2000 by Mosby, Inc. 1079-2104/2000/$12.00 + 0 7/16/104217 doi:10.1067/moe.2000.104217 Fig 1. Overview of Ortho-CT equipment. I.I.; imaging intensifier. Dentistry. Development was completed in 1997, and its clinical application has already been reported.11-14 In this study, we used Ortho-CT for the diagnosis of various conditions in the region of oral and maxillofa509 510 Terakado et al ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY April 2000 Fig 2. Three-dimensional sectional images by Ortho-CT. Range of reconstruction is a rectangular parallelepiped with height of 32 mm and width of 38 mm. Minimal unit that constitutes image (voxel) is a cube with a side measurement of 0.136 mm. Fig 3. Case 1: intraoral radiograph of radicular cyst. Radiolucent lesion with corticated border is observed in apical region of right upper first molar. Continuity of floor of maxillary sinus cannot be confirmed. cial surgery to confirm the usefulness of this method in the diagnosis. APPARATUS AND METHODS A dental multifunctional tomographic unit (Scanora, Soredex, Orion Co, Helsinki, Finland) was altered by equipping it with an imaging intensifier in the portion of the unit that holds the film (Fig 1). The exposure time is 17 seconds, and the radiograph is taken at 85 kV and 10 mA by using an attached filter of 1 mm copper.11,12 Reconstruction time of 3-dimensional images is about 10 minutes when a personal computer (Pentium II, 400 MHz) is used, and it takes about 30 minutes until the registration in the database is completed and images are printed out. The range of reconstruction takes the form of a cylinder with a height of 32 mm and a diameter of 38 mm, which is a body of rotation of a rectangular parallelepiped with a height of 32 mm and a width of 38 mm. The minimal unit that constitutes an image (voxel) is a cube with a side measurement of 0.136 mm. ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY Volume 89, Number 4 Terakado et al 511 Fig 4. Cross section focused on palatal root by Ortho-CT. Radicular cyst is observed in relation to palatal root of first molar. Continuity of floor of maxillary sinus can be confirmed. This sectional image was reconstructed from stored data from only one exposure. The minimal resolution of images is about 0.25 mm.11,12 The radiation doses are about 1⁄30 of those of conventional x-ray CT and are about the same as those of rotational panoramic radiography.12,13 Sectional images can be obtained in any direction, at any tomographic layer, and at any interval within the range of the cylinder. Sections parallel to the dental arch (parallel sections), perpendicular to the dental arch (cross sections), and horizontal sections are produced with a slice width of 1 mm at an interval of 1 mm.11,12 The representative images can be registered in a database and printed out (Fig 2). This imaging system was used for the diagnosis of diseases that occurred in the oral and maxillofacial region. RESULTS Some representative cases showing the usefulness of 3-dimensional images by Ortho-CT are presented. Case 1: Radicular cyst near the floor of the maxillary sinus The patient was a 44-year-old woman who had swelling and pain in the palatal gingiva of the maxillary first molar on the right side. The intraoral radiograph (Fig 3) and rotational panoramic radiograph revealed a radiolucent lesion in the apical region of the right maxillary first molar. The continuity of the floor of the maxillary sinus was not confirmed with either of these radiographs. Ortho-CT revealed a low density lesion around the apex of the palatal root of this tooth, Fig 5. Case 2: intraoral radiograph. Horizontal fracture line (white arrow) is observed in middle third of root of left maxillary central incisor. and the continuity of the floor of the maxillary sinus was observed clearly (Fig 4). During surgery it was confirmed that there was a layer of bone between the cyst and the maxillary sinus without perforation of the 512 Terakado et al ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY April 2000 A B Fig 6. Parallel sectional images by Ortho-CT. A, Fracture line is observed only in labial side of root of left maxillary central incisor. B, Widening of periodontal ligament space in labial side of root of right maxillary central incisor is seen clearly. maxillary sinus and that the cyst was attached to the palatal root of the tooth. Case 2: Trauma of the anterior region in the maxilla (root fracture and dislocation of teeth) The patient was a 21-year-old woman who fainted on the street because of anemia. Her face was hit hard on impact. Oral examination revealed that the right maxillary lateral and left maxillary central incisors were displaced toward the palatal side. Intraoral radiography revealed a radiolucent line indicating a horizontal fracture in the left maxillary central incisor in the middle third of the root (Fig 5). Successional Ortho-CT images with an interval of 1 mm revealed that the fracture line was present only on the labial side of the root of the left maxillary central incisor (Fig 6, A), and there was widening of the periodontal ligament space of the right maxillary central and lateral incisors caused by dislocation (Fig 6, B). After the incisors were repositioned, the teeth were fixed with a splint for 4 weeks to allow natural healing. The left maxillary central incisor did not show any response to electrical pulp test. However, because the fracture line was present only on the labial surface (confirmed with successional Ortho-CT images), and because there were no other symptoms (such as discoloration and widening of the periodontal ligament ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY Volume 89, Number 4 Terakado et al 513 Fig 7. Case 3: rotational panoramic radiograph (enlarged). Fracture line may be seen at base of left mandibular neck, although displacement of fracture is not confirmed. Fig 8. Cross sectional image of mandibular head by Ortho-CT. Detachment of left mandibular head from mandibular body and displacement to lateral side are observed. space), the patient was simply observed. The electrical pulp test became positive 3 months after injury. Case 3: Fracture of the mandibular head The patient was a 30-year-old woman who sustained injury to her face from falling. The patient complained of discomfort in the temporomandibular joints on closing the mouth. On physical examination, the midline of the mandible was found to be displaced slightly leftward, and slight pain on pressure was noted in the temporomandibular joint region. On the rotational panoramic image, the left mandibular head showed changes in position and morphology, but the fracture line was not seen clearly (Fig 7). OrthoCT revealed that there was a fracture line in the mandibular neck and that the mandibular head was displaced with the top of the head inclined inward and detached 514 Terakado et al A ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY April 2000 B Fig 9. Case 4: inverted median supernumerary impacted tooth (mesiodens) is observed on intraoral (A) and occlusal (B) radiographs. from the mandibular body (Fig 8). The patient was treated by closed repositioning and intermaxillary fixation by using splints. Case 4: Median supernumerary impacted tooth (mesiodens) in the maxilla The patient was a 7-year-old girl. There were no particular findings except for approximately 1 mm of separation between the upper left and right central incisors. Intraoral (Fig 9, A) and occlusal radiography revealed an inverted median supernumerary impacted tooth, the crown of which might be in the palatal side in the occlusal radiograph (Fig 9, B). Ortho-CT revealed an inverted supernumerary tooth on the palatal side with the apex curved toward the labial side in the parallel section (Fig 10, A), approaching the incisive foramen and the bilateral maxillary central incisors in the horizontal section (Fig 10, B). For treatment, the supernumerary tooth was extracted from the palatal side so as not to injure the apexes of the maxillary central incisors. Case 5: Presurgical evaluation of osseointegrated implants The patient was a 52-year-old man. Presurgical examination was performed before inserting implants in the edentulous part of the left lower posterior region. On oral examination, the gingiva in the edentulous part appeared healthy, presenting no particular abnormal findings. On rotational panoramic radiography, no abnormal findings were found, such as resorption of the jaw bone (Fig 11). By using Ortho-CT, the location of the mandibular canal was clearly observed on parallel section and that of the mental foramen on cross section around the premolar region (Fig 12). There were also no abnormal findings in the buccal and lingual cortical bone and cancellous bone of the mandible. The mandibular canal was more clearly seen on cross sections at the premolar region. With OrthoCT, measurement of the distance can be easily performed at any site by using a scale shown on the left side of the image. In this case, the distance between the alveolar ridge to the mandibular canal could be measured. Location of the mandibular canal and complex morphology of the jaw bone were observed on cross sections in the molar region. DISCUSSION When making a diagnosis and treating a variety of diseases in the region of the jaws, the lesion and the area around the lesion should be carefully examined before surgery because the maxillofacial region is characterized by complex anatomic structures and morphology.1,2 Because of the recent progress of computer technology, 3-dimensional reformatting has become possible by using serial 2-dimensional CT images, allowing location and morphology to be examined 3dimensionally.3-7 Thus the pathologic condition of the ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY Volume 89, Number 4 Terakado et al 515 A B Fig 10. Sectional images by Ortho-CT. Inverted supernumerary tooth is observed on palatal side with apex being curved toward labial side. A, Parallel section to dental arch. B, Horizontal section. lesion can be accurately examined, decreasing differences in the interpretation among individual observers.3 However, the currently used 3-dimensional CT scanners are large and costly. Furthermore, the radiation dose for conventional x-ray CT may be more than 10 times that of plain radiography, which is also a matter of concern.1 When slice width is shortened to obtain more accurate data, the radiation dose increases even more. The unit used in this study was a dental tomographic unit equipped with a small imaging intensifier.10,11 This is a small CT unit that is optimal for dental use. The x-ray tube and imaging intensifier rotate 360° around the patient for 17 seconds until the image data are acquired, which makes patient positioning compar- atively easy and minimizes patient motion. The radiation dose, which is often problematic in radiologic imaging diagnosis, is less than 1⁄30 of that of CT in examining the same range of area.13 For example, the effective doses at the maxillary sinus examination were approximately 8.5 µSv per examination by Ortho-CT, whereas they were 270 µSv per examination by conventional CT. As for the image resolution, because minute changes need to be detected in examining diseases in the dental field, conventional units were not necessarily satisfactory.7 However, for the Ortho-CT scanner used in this study, the exposure field is 32 mm high and 38 mm wide and can provide parallel sections and cross sections of the dental arch (which is curved) 516 Terakado et al ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY April 2000 Fig 11. Case 5: No abnormal findings are seen in edentulous region on rotational panoramic radiograph. or of any other target. For example, in examining the posterior region of the maxilla, accurate images of high resolution parallel to both palatal root and buccal roots were obtained. In Case 1, a radiolucent lesion was noted in the apical region on the intraoral radiograph, and the presence of thin bone between the low density lesion and the maxillary sinus was confirmed with successional Ortho-CT images. It was also revealed that the lesion originated from the palatal root. By using Ortho-CT, any tomographic image (eg, the image focused on the palatal root) can be reconstructed easily from the data stored in the computer by only one exposure. This is an important advantage of Ortho-CT compared with conventional x-ray CT. It is very effective in reducing the patient’s radiation dose. In case 1, by using this information, tooth extraction and cyst enucleation were performed, avoiding cutting unnecessary bone or perforation of the maxillary sinus. When Ortho-CT is applied to the mandible, important information concerning the positional relationship between the lesion and the mandibular canal can be obtained before surgery. In Case 4, the direction of eruption of the supernumerary tooth and its positional relationships with the proximal teeth and incisive canal could be examined in detail before surgery, facilitating smooth treatment without inflicting injury on the adjacent tissues. In Case 2, as it was revealed that the fracture line was present only on the labial surface, conservative treatment without pulpectomy was selected, and later, pulp response was confirmed. In Case 3, though fracture was in doubt by the conventional rotational panoramic radiography, a clear fracture line and dislocation of the left mandibular head were confirmed by Ortho-CT. In cases like this, a posterior-anterior view is usually taken, but because the radiation dose was so low, Ortho-CT was taken without a posterior-anterior view. Image data of Ortho-CT can be printed out at the actual size, allowing measurement of actual values.11,12 In addition, by using the scale shown on the left side of the image, any distance can be measured.11,12 In Case 5, Ortho-CT was used for presurgical evaluation of dental implant. By this method, not only was the distance between the ridge of the alveolar bone to the mandibular canal measured, but also the positional relationship between the mental foramen and mandibular canal, thickness of the cortical bone, and trabecular pattern of the cancellous bone could be observed. In this study, we used Ortho-CT in evaluating the oral and maxillofacial region. In comparison with the conventional methods, the resolution was high in examining a small area, and the extent of the lesion and positional relationships with the maxillary sinus, mandibular canal, and proximal teeth could be examined. Actual value measurement was also possible. Thus more accurate data for diagnosis could be obtained. The differences in interpretation of the data among individual observers were very few, which was useful in deciding treatment plans. We believe that clinical application of Ortho-CT in the field of oral and maxillofacial surgery will become widespread because of its ability to produce low-dose, Terakado et al 517 ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY Volume 89, Number 4 A B Fig 12. Sectional images by Ortho-CT. A, Parallel section to dental arch. Location of mandibular canal (arrowhead) is seen clearly. B, Cross section to dental arch. Mental foramen (arrow) and condition of cortical bone are observed clearly. high-resolution, 3-dimensional images from any tomographic image stored in the computer without reexposure when a sightly different view is needed. REFERENCES 1. DelBalso AM, Hall RE, MarGarone JE. Radiographic evaluation of maxillofacial trauma. In: Delbalso AM, editor. Maxillofacial imaging. Philadelphia: WB Saunders; 1990. p. 35-49. 2. Poyton HG, Pharoah MJ, editors. Oral Radiology. Toronto: BC Decker Inc; 1989. p. 74-81. 3. Terakado M, Iwakami K, Nakada T, Horibe T, Nakazawa H, Kozaki T, et al. A clinical study of three-dimensional computer tomography of the oral and maxillofacial region. Nihon Univ Dent J 1998;72:640-8. 4. Mancuso AA, Hanafee WN, Kirchnes JA. Computed tomog- 5. 6. 7. 8. 9. raphy and magnetic resonance imaging of the head and neck. Baltimore: Williams and Wilkins; 1985. p. 42-60. Bonnier L, Ayadi K. Three-dimensional reconstruction in routine computerized tomography of the skull and spine. Experience based on 161 cases. J Neuroradiol 1991;18:250-61. Weeks PM, Vannier MW, Stevens WG, Gayou D, Gilula LA. Three-dimensional imaging of the wrist. J Hand Surg 1985; 10A:32-9. Vannier MW, Hildebolt CF, Conover G, Knapp RH, Crothers NY, Wang G. Three-dimensional dental imaging by spiral CT. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1997;84:561-70. Fishman EK, Drebin B, Media D, Scott WW, Ney DR, Brooker AF, et al. Volumetric rendering techniques. Application for threedimensional imaging of the hip. Radiology 1987;163:737-8. Schimming R, Eckelt U, Kittner T. The value of coronal computer tomograms in fractures of the mandibular condylar process. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1999;87:632-9. 518 Terakado et al ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY April 2000 10. Altini M, Coleman H, Kieser J, Kola H, Sneider P. Three-dimensional computed tomography reconstruction in treatment planning for large ameloblastoma. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1996;81:619-22. 11. Arai Y, Tammisalo E, Iwai K, Hashimoto K, Shinoda K. Development of Ortho Cubic Super High Resolution CT (OrthoCT). Lemke HU, Vannier MW, Inamura K, Farman AG, editors. Computer assisted radiology and surgery. Amsterdam: Elsevier; 1998. p. 780-5. 12. Arai Y, Tammisalo E, Iwai K, Hashimoto k, Shinoda K. Development of a compact computed tomographic apparatus for dental use. Dentomaxillofac Radiol 1999;28:245-8. 13. Iwai K, Arai Y, Nishizawa K, Tammisalo E, Hashimoto K, Shinoda K. Estimation of radiation doses from Ortho cubic super high resolution CT. Dentomaxillofac Radiol 1998;27:39. 14. Honda K, Hashimoto K, Arai Y, Iwai K, Tammisalo E, Shinoda K. Clinical experience with Ortho-CT for the diagnosis of the temporomandibular joint disorders. Dentomaxillofac Radiol 1998;27:39. Reprint requests: Koji Hashimoto, DDS, PhD Department of Radiology Nihon University School of Dentistry 1-8-13 Kanda Surugadai, Chiyoda-ku Tokyo, 101-8310 Japan [email protected] CALL FOR REVIEW ARTICLES The January 1993 issue of Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology, and Endodontics contained an Editorial by the Journal’s Editor in Chief, Larry J. Peterson, that called for a Review Article to appear in each issue. These Review Articles should be designed to review the current status of matters that are important to the practitioner. These articles should contain current developments, changing trends, as well as reaffirmation of current techniques and policies. Please consider submitting your article to appear as a Review Article. Information for authors appears in each issue of Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology, and Endodontics. We look forward to hearing from you.