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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
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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.
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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
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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
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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
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A
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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
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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)
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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
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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.
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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]
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