Download Cone beam CT and conventional tomography for the detection of

Dentomaxillofacial Radiology (2007) 36, 192–197
q 2007 The British Institute of Radiology
http://dmfr.birjournals.org
RESEARCH
Cone beam CT and conventional tomography for the detection
of morphological temporomandibular joint changes
H Hintze*,1, M Wiese1,2 and A Wenzel1
1
Department of Oral Radiology, School of Dentistry, University of Aarhus, Aarhus, Denmark; 2Department of Radiology, School of
Dentistry, University of Copenhagen, Copenhagen, Denmark
Objective: To compare the diagnostic accuracy of cone beam CT images with conventional
tomographic images for the detection of morphological temporomandibular joint (TMJ) changes.
Methods: 80 dry human skulls were scanned using a NewTomw 3G scanner and lateral and frontal
reconstructions of the right and the left TMJs were performed. In addition, lateral and frontal crosssectional tomograms of the skulls’ TMJs were obtained in a Cranex Tome unit with Digora storage
phosphor plates. Naked-eye inspection of the TMJs performed by three observers served as the gold
standard for the true presence of morphological changes. The mandibular fossae were excluded from
the study due to few changes in this joint component. The NewTomw and the conventional
tomographic images were examined by three independent observers using a binary scale for the
presence of morphological changes in the condyle (flattening, defects and osteophytes) and the
articular tubercle (flattening and defects). The accuracy for the different types of changes in relation
to the condyles and the articular tubercles was expressed as sensitivity and specificity values,
whereas the diagnostic accuracy for a general assessment including all changes in both joint
components was expressed by the sum of cases where the gold standard and the radiographic scores
were not identical (absolute difference). Differences between the two radiographic modalities were
tested by paired t-test.
Results: Detection of the various types of morphological changes in relation to the condyle and
the articular tubercle assessed separately resulted in no significant differences between the two
radiographic modalities, with the exception of bone defects in the articular tubercle examined on
frontal views alone where the specificity with tomography was significantly higher than with cone
beam CT. Detection of all morphological changes in relation to both the condyle and the articular
tubercle showed a significantly higher accuracy with tomography than with cone beam CT using
lateral views alone, but there was no significant difference between the two modalities using frontal
views alone and lateral and frontal views in combination.
Conclusion: In general, no significant differences in diagnostic accuracy for the detection of bone
changes in the condyle and in the articular tubercle were found between cone beam CT images and
conventional tomograms.
Dentomaxillofacial Radiology (2007) 36, 192–197. doi: 10.1259/dmfr/25523853
Keywords: radiography; temporomandibular joint (TMJ); digital radiography; cone beam CT;
NewTom
Introduction
Recently, cone beam CT (CBCT) for dental and maxillofacial
diagnostic osseous tasks has been developed as an alternative
to conventional CT. The CBCT technology results in images
*Correspondence to: Hanne Hintze, Department of Oral Radiology, School of
Dentistry, Faculty of Health Sciences, University of Aarhus, Vennelyst Boulevard 9,
DK-8000 Aarhus C, Denmark; E-mail: [email protected]
Received 9 February 2006; revised 30 June 2006; accepted 3 July 2006
of CT-like quality obtained on the basis of less expensive
equipment and components, shorter patient examination time
and much lower radiation dose than required for conventional
CT.1 – 5 In addition, the scanning procedure of the patient and
the software for image reconstruction connected with CBCT
are very user-friendly.
During the past few years, CBCT systems have been
introduced in many dental institutions (schools, centres,
TMJ radiography
H Hintze et al
special clinics etc.). Here, the CBCT technology serves as a
supplement to or a substitute for the traditional radiographic methods. Since the effective radiation dose with
CBCT is still higher than with many of the traditional
radiographic methods, such as full-mouth series and
panoramic and skull views, CBCT should substitute for
such examinations only in case its superiority (higher
diagnostic accuracy, higher reproducibility etc.) outweighs
its increased potential biological radiation risk to the
patient. To assess when CBCT is preferable in dental
patients, it is important to compare the accuracy of CBCT
for all relevant diagnostic tasks with the traditionally
applied methods.
So far, CBCT performed with the NewTomw (NIM,
Italy) and the Accuitomo (Morita Co., Japan) scanners has
been found to be superior to panoramic radiography for the
depiction of the inferior alveolar nerve6 and for the
identification of artificially made bone defects in pigs
and dry human mandibles.7 In addition, CBCT performed
with one of the above-mentioned scanners has been
claimed to be effective for implant planning,8 – 10 postoperative assessment of zygomaticomaxillary fractures,11
localization of maxillary unerupted canines,12 assessment
of the thickness of the roof of the glenoid fossa13 and
examination of the temporomandibular joint (TMJ),14 but
the method’s diagnostic accuracy in comparison with
traditionally applied methods such as linear and spiral
tomography and perhaps stereo-scanography, has not been
evaluated.
The aim of the present study was to compare the
diagnostic accuracy of CBCT performed with the
NewTomw 3G scanner with conventional tomography
obtained with the Cranex Tome unit for the detection of
morphological bone changes in the TMJ in dry human
skulls, from which the true presence of changes could be
validated by direct visual inspection.
Materials and methods
The left and right TMJs in 80 dry human skulls were
scanned in a NewTomw 3G CBCT scanner (NIM s.r.l.,
Verona, Italy) using the 9 inch detector field and automatic
exposure parameters depending on bone volume and
density. The scanner operates at 110 kV (constant),
0.5 mA and an exposure time which varied between 5 s
and 7 s. Each skull was positioned on a cast pillow placed
in the scanner’s gantry. The skull’s mid-sagittal plane was
aligned with the scanner’s medial light beam, whereas the
lateral light spot was centred at the level of the left condyle.
Cotton rolls were placed between the skull’s maxillary and
mandibular teeth or the edentulous jaws to separate the
condyle from direct contact with the mandibular fossa. A
radiographer, a radiologist and two dental students under
supervision performed the scans. The primary reconstruction of the raw data was restricted to the TMJ region
(approximately 1 cm superior to the mandibular fossa and
1 cm inferior to the condylar neck), and a series of axial
views of 1 mm thickness were automatically generated. On
one of those axial views the long axis of the examined
193
condyle was traced, and the software generated lateral and
frontal cross-sectional reconstructions perpendicular and
parallel to the long axis of the condyle, respectively. The
thickness of the image slices was 1 mm and the distance
between slices was 0.5 mm for both lateral and frontal
reconstructions.
Conventional spiral tomography was performed as
individually corrected (based on a lateral four angle “preexamination”) lateral (image plane perpendicular to the
long axis of the condyle) and frontal (image plane parallel
to the long axis of the condyle) tomograms in a Cranex
Tome X-ray unit (Soredex, Helsinki, Finland) using
photostimulable phosphor plates, which were scanned in
a Digora PCT scanner (Soredex). For information about
exposure settings and for more details, see Wiese et al.15
The skulls were placed on a photostat device to ensure
correct positioning. The lateral tomograms were obtained
with the mandible in a stable dental occlusion. Silicone
impression was used to obtain a stable occlusion in case of
tooth loss. The frontal tomograms were performed with the
condyle positioned below the articular tubercle. A
radiographer performed the tomographic examinations.
Three pre-calibrated observers examined the lateral and
the frontal images from both radiographic modalities
individually. On lateral images, the condyle was assessed
for the presence of flattening, defect and osteophyte,
whereas the mandibular fossa and the articular tubercle
were assessed for the presence of flattening and defect. On
frontal images, only the condyle and the articular tubercle
were assessed for the presence of flattening and defect.
Flattening was defined as loss of convexity of the bone
outlines, defect as a local area of rarefaction in the layer of
compact bone and osteophyte as a local outgrowth of bone
arising from the mineralized surface.16 Multiple examples
of flattening, defects and osteophytes in TMJ tomograms
were collected in an atlas, which the observers could
consult in case they were in doubt how manifest changes
should be scored as present. The CBCT images were
assessed in the NewTomw 3G software on a 19 inch Philips
flat screen monitor, whereas the tomograms were assessed
in the Digora software on a 19 inch IBM CRT monitor.
Both monitors were placed in rooms with subdued lighting.
The observers could use the enhancement facilities in the
respective software as they liked. Two experienced oral
radiologists (Observer1 and Observer 2) and one general
dentist under specialist training (Observer 3) independently examined the lateral and the frontal images of each
joint obtained with the two modalities. The left and the
right joints in each skull were examined independently of
each other, and lateral and frontal cross-sectional views of
the same joint were also assessed independently of each
other. A binary registration scale was used with the
following scores: 0, not certain of change; 1, certain of
change.
15 randomly selected joints were assessed a second time
(3 – 4 weeks after the first assessment) with both radiographic modalities to evaluate the intraobserver
reproducibility.
Several months prior to the radiographic examinations,
the joints had been validated for the presence of
Dentomaxillofacial Radiology
TMJ radiography
H Hintze et al
194
differences was termed the absolute difference and was
calculated for lateral and frontal views separately, and for
the two projections in combination. To evaluate the
accuracy of the combined views, flattening and defects,
which could appear in both projections, were defined to be
present if they were recorded just from one of the
projections, whereas changes appearing in one projection
only were included in case they were recorded from the
relevant projection. The lower the absolute difference, the
higher the diagnostic accuracy. Differences between
modalities were tested by paired t-test and differences
between observers were tested by variance analysis
(ANOVA). The level of significance was P , 0.05.
Intraobserver reproducibility for recordings obtained
from lateral and frontal views in combination was
expressed as kappa values.
Table 1 Frequency of morphological changes in accordance with the
gold standard
Condyle
Mandibular fossa
Articular tubercle
Flattening %
(n)
Defects %
(n)
Osteophytes %
(n)
Total
40.3 (64)
0.6 (1)
3.8 (6)
58.5 (93)
4.4 (7)
15.1 (24)
8.2 (13)
Not assessed
Not assessed
159
159
159
morphological changes by the same three observers.
A calibration session preceded the individual observer
examination. The surfaces of the skulls’ condyles,
mandibular fossae and articular tubercles were examined
by naked-eye inspection for the presence of macroscopic
flattening, defect and osteophyte using a magnifying
viewer with built-in light. “Score 0” indicated “not certain
of change” and “Score 1” indicated “certain of change”. A
change was defined as present if reported by at least two of
the three observers. The naked-eye inspection served as the
gold standard for the radiographic examinations.
Results
One joint missed conventional tomography in the frontal
plane and was excluded from the study sample, which
thereafter included 159 joints. The frequency of morphological changes according to the gold standard in the
condyles, mandibular fossae and articular tubercles is
shown in Table 1. Since the number of changes in relation
to the mandibular fossa was very low, the results for this
joint component were excluded.
In Figure 1, the mean absolute difference of all
morphological changes in relation to the condyle and the
articular tubercle is shown. On lateral views alone and on
lateral and frontal views in combination, the absolute
difference with CBCT was higher than with conventional
spiral tomography, whereas the opposite was found using
frontal views alone. However, only the difference found on
lateral views alone was significant (P ¼ 0.044).
The diagnostic accuracy of changes in the condyle (Table 2)
showed no significant difference between the two modalities
Data analysis
The diagnostic accuracy for the detection of flattening,
defects and osteophytes in the various joint components on
lateral and frontal views separately was expressed as the
sensitivity and specificity, and differences between the two
radiographic modalities were tested by paired t-test (SPSS
package, GLM, version 10.0 for Windows; SPSS Inc.,
Chicago, IL). To express the general diagnostic accuracy
for all changes in each joint component and in all joint
components as a whole, the sum of non-matching gold
standard and radiographic scores was used. The sum of
non-matching scores was calculated for each possible
change by counting the number of score differences of þ 1
and 2 1 (subtracting the radiographic score from the gold
standard score). A score difference of þ 1 expressed a
false-negative recording whereas a score difference of 2 1
expressed a false-positive recording. The sum of
250
Mean absolute difference
200
150
100
50
0
Lateral views
Frontal views
CBCT
Lateral+Frontal views
Tomo
Figure 1 Mean observer diagnostic accuracy for the detection of all morphological changes in the condyles and the articular tubercles on lateral views,
frontal views and lateral and frontal views in combination using cone beam CT (CBCT) and conventional spiral tomography (Tomo) (*significant
difference, P ¼ 0.044)
Dentomaxillofacial Radiology
TMJ radiography
H Hintze et al
195
Table 2 Diagnostic accuracy for the detection of morphological changes in the condyle using cone beam CT (CBCT) and conventional spiral
tomography (Tomo) and P-values for their comparison
Lateral projection
Frontal projection
Flattening
Mean sensitivity
Mean specificity
Defect
Osteophyte
Flattening
Defect
CBCT
Tomo
P-value
CBCT
Tomo
P-value
CBCT
Tomo
P-value
CBCT
Tomo
P-value
CBCT
Tomo
P-value
0.23
0.87
0.11
0.95
0.21
0.22
0.15
0.95
0.15
0.97
0.83
0.18
0.15
0.96
0.15
0.99
–
0.43
0.40
0.90
0.23
0.94
0.52
0.25
0.20
0.96
0.21
0.95
0.94
0.67
on both lateral and frontal views. The mean observer
sensitivities for the various types of changes were generally
low, since they ranged from 0.11 for flattening on lateral
conventional spiral tomography views to 0.40 for defects on
frontal CBCT views. In contrast, the mean specificities for the
same changes were high, ranging from 0.87 for flattening on
lateral CBCT views to 0.99 for osteophytes on lateral
conventional spiral tomography views. Mean sensitivity and
specificity values for changes in relation to the articular
tubercle are shown in Table 3. Also in this joint component, no
significant differences in diagnostic accuracies were found
between CBCT and conventional spiral tomography. Only for
the detection of defects on frontal views did conventional spiral
tomography show a significantly higher specificity than
CBCT. The tendency for low senstivity and high specificity
values as found for changes in the condyle was valid also for the
articular tubercle. In particular, defects were very difficult to
identify.
The individual observer performance with the two
radiographic modalities using lateral and frontal views in
combination can be seen in Figure 2. No significant
differences in observer performances were found for the
detection of changes in relation to the condyle and the
articular tubercle, or the two components assessed together
with any of the two radiographic modalities. The most
manifest observer variation was seen for assessment
of condylar changes with conventional spiral tomography
and here the variation was mainly caused by large
(non-significant) variations for the detection of bone
defects.
Kappa values for intraobserver reproducibility for the
detection of morphological changes in relation to the
condyle and the articular tubercle assessed together from
lateral and frontal views in combination ranged as follows
for CBCT and conventional spiral tomography: Observer
1: 0.55 – 1.00 and 0.66 – 1.00; Observer 2: 0.32 – 1.00 and
0.32 – 1.00; Observer 3: 1.00 (no range) and 0.87 – 1.00.
Discussion
In general, tomography is considered the most accurate of
the traditional radiographic techniques for imaging of the
TMJ.17 – 20 To obtain the most realistic images of the joint
components, the examination ought to be orientated
perpendicular and/or parallel to the long axis of the condyle.
This requires a pre-examination of the joint from which the
angulation of the long axis can be assessed. This, in addition
to the fact that multiple tomographic cuts are often needed to
examine the joint from the most lateral to the most medial
part in the lateral projection and from the most anterior to
the most posterior part in the frontal projection, might well
result in high patient radiation doses. Moreover, the
examination procedure for a bilateral TMJ tomography in
two planes is time-consuming and occupies the radiographic unit for a long period of time.14 In case the
diagnostic accuracy of TMJ changes is not jeopardized,
many advantages could be obtained with the use of
the CBCT technique. A CBCT examination with the
NewTomw 3G scanner is definitely much shorter, includes
image data for both the right and left TMJs from a single
3608 rotation scan around the patient’s head and simplifies
patient positioning, and the radiation dose may be lower
than for multiple-cuts tomography. The latter has not been
evaluated yet, but from a recent study the radiation dose
needed for a 9 inch NewTomw 9000 scan was found to
correspond to the dose from two to four or from three to
seven panoramic radiographs, depending on whether the
effective organ doses included or excluded the salivary
glands.21 In comparison with a panoramic exposure, a onecut tomography examination performed in the posterior part
of the jaws using rectangular collimation has been found to
require about the same dose.22,23 In the present study, an
average of four tomographic cuts in both the lateral and
frontal planes were exposed for each TMJ. In addition, scout
images preceding the actual tomography were needed
and obtained. All in all, a conventional bilateral TMJ
Table 3 Diagnostic accuracy for the detection of morphological changes in the articular tubercle using cone beam CT (CBCT) and conventional spiral
tomography (Tomo) and P-values for their comparison (significant value is marked in bold)
Lateral projection
Frontal projection
Flattening
Mean sensitivity
Mean specificity
Defect
Flattening
Defect
CBCT
Tomo
P-value
CBCT
Tomo
P-value
CBCT
Tomo
P-value
CBCT
Tomo
P-value
0.28
1.00
0.39
0.99
0.52
0.74
0.03
0.98
0.03
0.98
1.00
0.42
0.12
1.00
0.17
1.00
0.87
0.42
0.07
0.96
0.06
0.99
0.42
0.02
Dentomaxillofacial Radiology
TMJ radiography
H Hintze et al
196
Absolute difference
200
150
100
50
0
CBCT-Condyle
Tomo-Condyle
CBCT-Tubercle
Observer 1
Tomo-Tubercle
Observer 2
CBCTTomoCondyle+Tubercle Condyle+Tubercle
Observer 3
Figure 2 Diagnostic accuracy of each observer for the detection of morphological changes in the condyles, the articular tubercles and the condyles and the
articular tubercles assessed together on lateral and frontal views in combination using cone beam CT (CBCT) and conventional spiral tomography (Tomo)
tomographic examination might well require a much higher
dose than needed for CBCT.
From the present results, no general significant difference
in diagnostic accuracy was found between CBCT and
conventional spiral tomography. Evaluation of the two joint
components separately showed the same result, with the
exception of the detection of bone defects in the articular
tubercle on frontal views, where the specificity was
significantly higher with the conventional spiral tomography
modality than with CBCT. The difference in specificity was,
however, only 3% and such a small variation will probably
not have any consequences in the clinic.
For both radiographic modalities, it was striking to see
how ineffective they were for the identification of flattening,
defects and osteophytes. Condylar flattening was present in
40% of the 159 examined joints in accordance with the gold
standard but, from lateral views, on average only 23% was
identified correctly with CBCT and on average 11% with
conventional spiral tomography. Using frontal views for
assessment of the same change, this percentage increased to
on average 40% with CBCT and on average 23% with
conventional spiral tomography, but still the percentages
were disappointingly low. However, the higher sensitivity
obtained from frontal views ought to motivate the clinician
to order such a projection as a supplement to the lateral view
when the TMJ is to be examined. This recommendation is in
agreement with conclusions from previous studies on
effective projections for the assessment of the
TMJ.14,17,24,25 However, frontal views cannot replace lateral
views since condylar anterior osteophytes might be visible
on lateral views only. The insignificant differences between
sensitivity values for the detection of condylar flattening
with the two modalities were not ascribed to the different
positions of the skulls’ mandibles during examination. If
this had had an influence on the recordings of the images,
variations between the accuracy values for the other
morphological changes would also be expected, but such
differences were not found.
For the identification of condylar defects and osteophytes, the sensitivities were lower than the values for
flattening, whereas the specificities were high. This result
indicates that only a minority of truly present condylar
defects and osteophytes are correctly identified, while the
majority of normal condyles (without defects and osteophytes) are correctly identified as sound. This finding was
also valid for flattening and defects in the articular tubercle.
For a general assessment of the TMJ, no significant
differences in diagnostic accuracy were found between
the observers with either of the two modalities. The
variation in intraobserver agreement for all three
observers for the assessment of the various changes in
the two joint components was about the same with both
modalities. This observation was somewhat surprising
since the observers were rather familiar with conventional tomograms, but completely unfamiliar with CBCT
for TMJ examinations. This might indicate that NewTom images are very reader-friendly and easy to
become familiar with.
In conclusion, generally no significant differences in
diagnostic accuracy for the detection of morphological
bone changes in relation to the condyle and the articular
tubercle were found between images from cone beam CT
obtained with the NewTomw 3G scanner and conventional
cross-sectional tomography obtained with the Cranex
Tome unit. If the present results are also valid for patients,
the modality requiring least radiation dose and being most
convenient for the patient and the radiographic staff ought
to be used.
References
1. Preda L, Di Maggio EM, Dore R, La Fianza A, Solcia M,
Schifino MR, et al. Use of spiral computed tomography for
multiplanar dental reconstruction. Dentomaxillofac Radiol 1997;
26: 327 – 331.
Dentomaxillofacial Radiology
2. Cohnen M, Kemper J, Mobes O, Pawelzik J, Modder U. Radiation
dose in dental radiology. Eur Radiol 2002; 12: 634 –637.
3. Danforth RA, Dus I, Mah J. 3-D volume imaging for dentistry: a new
dimension. J Calif Dent Assoc 2003; 31: 817 – 823.
TMJ radiography
H Hintze et al
4. Hashimoto K, Arai Y, Iwai K, Araki M, Kawashima S, Terakado M. A
comparison of a new limited cone beam computed tomography machine
for dental use with a multidetector row helical CT machine. Oral Surg
Oral Med Oral Pathol Oral Radiol Endod 2003; 95: 371–377.
5. Schulze D, Heiland M, Thurmann H, Adam G. Radiation exposure
during midfacial imaging using 4- and 16-slice computed tomography, cone beam computed tomography systems and conventional
radiography. Dentomaxillofac Radiol 2004; 33: 83 –86.
6. Pawelzik J, Cohnen M, Willers R, Becker J. A comparison of
conventional panoramic radiographs with volumetric computed
tomography images in the preoperative assessment of impacted
mandibular third molars. J Oral Maxillofac Surg 2002; 60: 979 –984.
7. Mengel R, Candir M, Shiratori K, Flores-de-Jacoby L. Digital volume
tomography in the diagnosis of periodontal defects: an in vitro study
on native pig and human mandibles. J Periodontol 2005; 76:
665 –673.
8. Hatcher DC, Dial C, Mayorga C. Cone beam CT for pre-surgical
assessment of implant sites. J Calif Dent Assoc 2003; 31: 825 –833.
9. Lascala CA, Panella J, Marques MM. Analysis of the accuracy of
linear measurements obtained by cone beam computed tomography
(CBCT-NewTom). Dentomaxillofac Radiol 2004; 33: 291 –294.
10. Aranyarachkul P, Caruso J, Gantes B, Schulz E, Riggs M, Dus I, et al.
Bone density assessments of dental implant sites: 2. Quantitative
cone-beam computerized tomography. Int J Oral Maxillofac Implants
2005; 20: 416 –424.
11. Heiland M, Schulze D, Rother U, Schmelzle R. Postoperative
imaging of zygomaticomaxillary complex fractures using digital
volume tomography. J Oral Maxillofac Surg 2004; 62: 1387 – 1391.
12. Walker L, Enciso R, Mah J. Three-dimensional localization of
maxillary canines with cone-beam computed tomography. Am J
Orthod Dentofacial Orthop 2005; 128: 418 –423.
13. Honda K, Arai Y, Kashima M, Takano Y, Sawada K, Ejima K, et al.
Evaluation of the usefulness of the limited cone-beam CT (3DX) in
the assessment of the thickness of the roof of the glenoid fossa of the
temporomandibular joint. Dentomaxillofac Radiol 2004; 33:
391 – 395.
14. Tsiklakis K, Syriopoulos K, Stamatakis HC. Radiographic examination of the temporomandibular joint using cone beam computed
tomography. Dentomaxillofac Radiol 2004; 33: 196 – 201.
15. Wiese, M., Hintze, H., Svensson, P., and Wenzel, A. Comparison of
diagnostic accuracy of film and digital tomograms for assessment of
morphological changes in the TMJ. Dentomaxillofac Radiol 2007;
36: 12 –17.
197
16. Omnell K-Å, Petersson A. Radiography of the temporomandibular
joint utilizing oblique lateral transcranial projections. Comparison of
information obtained with standardized technique and individualized
technique. Odont Revy 1976; 26: 77 – 92.
17. Tyndall DA, Davies KL, Ludlow JB. A comparison of zonography,
multidirectional tomography, and biplanar panoramic images for
detection of simulated condylar arthropathy of the temporomandibular joint. Int J Adult Orthod Orthognath Surg 1995; 10: 277 – 284.
18. Ludlow JB, Davies KL, Tyndall DA. Temporomandibular joint
imaging. A comparative study of diagnostic accuracy for the
detection of bone change with biplanar multidirectional tomography
and panoramic images. Oral Surg Oral Med Oral Pathol Oral Radiol
Endod 1995; 80: 735 – 743.
19. Cholitgul W, Petersson A, Rohlin M, Tanimoto K, Åkerman S.
Diagnostic outcome and observer performance in sagittal tomography
of the temporomandibular joint. Dentomaxillofac Radiol 1990; 19:
1– 6.
20. Brooks SL, Brand JW, Gibbs SJ, Hollender L, Lurie AG, Omnell KÅ, et al. Imaging of the temporomandibular joint. A position paper of
the American Academy of Oral and Maxillofacial Radiology. Oral
Surg Oral Med Oral Pathol Oral Radiol Endod 1997; 83: 609 –618.
21. Ludlow JB, Davies-Ludlow LE, Brooks SL. Dosimetry of two
extraoral direct digital imaging devices: NewTom cone beam CT and
Orthophos Plus DS panoramic unit. Dentomaxillofac Radiol 2003;
32: 229 –234.
22. Frederiksen NL, Benson BW, Sokolowski TW. Effective dose and
risk assessment from film tomography used for dental implant
diagnostics. Dentomaxillofac Radiol 1994; 23: 123 – 127.
23. Dula K, Mini R, van der Stelt PF, Sanderink GCH, Schneeberger P,
Buser D. Comparative dose measurements by spiral tomography for
preimplant diagnosis: the Scanora machine versus the Cranex Tome
radiography unit. Oral Surg Oral Med Oral Pathol Oral Radiol
Endod 2001; 91: 735 – 742.
24. Sato H, Fujii T, Yamada N, Kitamori H. The contribution of frontal
tomography to the diagnosis of temporomandibular joint osteoarthritis. Dentomaxillofac Radiol 1992; 21: 77 – 80.
25. Bouwman JPB, Kerstens HCJ, Tuinzing DB. Condylar resorption in
orthognathic surgery. Oral Surg Oral Med Oral Pathol 1994; 78:
138 – 141.
Dentomaxillofacial Radiology