REVERSE OPG - A REVIVAL. C. Pravda, D. Koteeswaran. - Aosr.co.in

C. Pravda * , D. Koteeswaran †
ABSTRACT
REVERSE OPG – A REVIVAL
Background: Reverse panoramic radiography is a radiographic technique to view the lateral aspect of the condylar head
and its neighboring structures more clearly and with less distortion. The technique is simple to perform with the patient
in the reverse position in an orthopantomogram particularly in a unit that does not have a provision to take a TMJ
tomogram.
Material & Methods: The machine used was Rotograph 230 of 1992 model. The chin rest was removed so that the
patient can be positioned posteriorly such that the condylar region is moved closer to the lateral centre of rotation within
a fixed distance between the X ray source and the cassette.
Results: The technique demonstrated the normal anatomy as well as the osteoarthritic changes in the condyle with
mouth opened and closed position.
Conclusion: Reverse panoramic radiograph is yet another radiographic technique to view the lateral aspect of the
condyle.
AOSR 2011;1(3):135-138.
Key words: Orthopantomogram, Mandibular condyle, Reverse Panoramic Radiograph
* Department of Oral Medicine and Radiology, Sathyabama University Dental College & Hospital, Jeppiaar nagar,
Old Mamallapuram Road, Chennai – 600 119.
† Department of Oral Medicine and Radiology, Meenakshi Ammal Dental College, Chennai.
Archives of Oral Sciences & Research
INTRODUCTION :
Panoramic radiography is a popular radiographic technique
in dentistry. It is an essential element in the radiographic
diagnosis. Panorama means an unobstructed region in any
direction. A panoramic film shows mandible and maxilla
from condyle to condyle in a single film.
Panoramic radiography was first described by Numata 1,2
and Paatero 3 independently and later by several others
like Hudson and Blackman. 4-6 The first commercial
orthopantomograph was available in 1961. Many
panoramic units are available in the market today. They
all primarily differ in the number and location of the
centre of rotation, the choice of fixed or adjustable focal
trough, type and shape of film transport mechanism. 7
Panoramic radiography is an invaluable aid in orofacial
diagnosis because of the broad coverage of the facial
bones and teeth. It also serves as a diagnostic modality
for hard tissue imaging of the temporomandibular joint.
Some panoramic units have a provision to take TMJ
Tomogram. To accomplish this, the unit must have an
adjustable focal trough which is set for the position of
the condyle.
There are several other radiographic techniques to
show the lateral aspect of the condyle but each technique
has its own limitations. The lateral skull and lateral
oblique shows much of superimposition and distortions.
Transcranial view shows the lateral joint contours.
The ipsilateral petrous ridge may superimpose over
the condylar neck. It also needs the use of a suitable
craniostat. Transpharyngeal view shows the sagittal
view of the medial pole of the condyle but needs the
mouth to be opened widely and it delivers a high
radiation dosage to the skin. Linear Tomography and
Computed Tomography cannot be used for general
screening purpose. Even a standard panoramic view
results in some degree of distortion and magnification
in the region of mandibular ramus. A reverse panoramic
radiograph provide a clearer and less distorted view of
the ascending mandibular ramus, condylar head and
adjacent structures especially when the mouth opening is
limited.
MATERIALS AND METHODS :
This technique was used on twenty patients who visited
the Out Patient Department of Meenakshi Ammal Dental
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C. Pravda et al.
College, Chennai to demonstrate the normal anatomy
as well as the osteoarthitic changes of the condyle. The
machine that was used for the study was Rotograph
230 of 1992 model. * Despite the advent of new
technological advancement and innovation this unit
is still in use to take OPGs and reverse OPGs. Certain
modifications were made in the machine. The chin rest
was removed so that the patient can be positioned
posteriorly such that the condylar region is moved
closer to the lateral centre of rotation within a fixed
distance between the X ray source and the cassette. The
procedure was explained to the patients regarding the
movement of the tube around the patient’s head. Patient
was asked to remove the eyeglasses, earrings, dentures,
hairpins, etc. Patient can sit or stand erectly in the machine
in the reverse position (Figure 1). The head was aligned
with the mid sagittal plane perpendicular to the floor.
The chin was slightly tilted down so that the Frankfort
line is parallel to the floor. Lateral head stabilizers
are used to ensure that the patient’s head is central.
Exposure is made with both mouth opened and
closed position. It should be remembered that if the
left and right markers are built-in the cassette, they will
be incorrect. So the film marking has to be altered.
Figure 2a : Normal radiographic anatomy – Standard
panoramic view.
Figure 2b : Normal radiographic anatomy – reverse panoramic
view.
Figure 1 : Patient positioned in a reverse direction in the
OPG machine. The unit is Rotograph 230 of 1992 model.
RESULTS :
Figure 3a : Position of the condyle in a reverse OPG –
Mouth opened position
This technique can demonstrate the normal anatomy as
well as the osteoarthritic changes in the condyle with
mouth opened and closed position. (Figure 2 and 3)
DISCUSSION :
Panoramic radiograph is a curved surface tomogram.
It is based on the principle of reciprocal movement of
an x ray source and an image receptor around a central
plane while the patient remains stationary. This central
plane of the object that is not blurred on the radiograph
is called as the plane of acceptable detail or image
layer.
Figure 3b : Position of the condyle in a reverse OPG -
Mouth closed position
*
Villa Sistemi Medicall Spa, Italy
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Reverse OPG
Patient positioning is critical and needs to be accurate
such that condylar region is close to the lateral centre
of rotation. The speed is reduced so that the image
layer moves closer to the centre of rotation and
becomes thinner resulting in a clearer and less distorted
view. This view is used especially when the mouth
opening is limited.
Errors in the technique mostly occur with improper
positioning of the patient.
Advantages
- Shows the condyle and its neighboring structures
with the ascending ramus that is usually overlapped
by the soft tissue shadows in the OPG
- The technique is simple to perform. Retakes are
possible. And quality control is easier to maintain.
- Requires minimum cooperation from the patient
- It practically eliminates problem in patient with
trismus or uncooperative patient
Limitations
- Reverse OPG is not without problems. Positioning
of the patient is more critical than for the standard
view.
- It is believed that this view increases the exposure
to the eye. It is precautious to use lead eye shields.
Direct measurement of the eye doses were made
using thermoluminescent dosimeters mounted on
a ‘Rando’ tissue equivalent skull phantom. † Dosimetric
studies shows that with correct positioning of the
patient the dose delivered appears on an average to
be very similar in both standard and reverse
technique and that there is no increase when using
the reverse method. (Table 1)
Table 1 : Comparison of dosages in Standard and reverse positions using ‘Rando’ phantom
Sites
Reverse cGy
Markus 8
Standard cGy
Williams 9
Standard cGy
Bartolotta 10 Standard cGy Wall 11
Left eye 0.003 0.002 0.002 0.002
Right eye O.003 0.002 0.002 0.002
Left external TMJ 0.010 0.007
Right External TMJ 0.007 0.006
Left Mastoid 0.006 0.006
Right mastoid 0.004 0.005
Back neck 0.002 0.008 0.100 0.12
Centre tongue 0.035 0.013 0.024 0.22
CONCLUSION :
Reverse panoramic radiograph is yet another radiographic
technique to view the lateral aspect of the
condyle especially in patients with limited mouth
opening and it can be taken with orthopantomographic
units that do not have the provision to take a TMJ
tomogram.
REFERENCES :
1. Numata H. Considerations of the parabolic radiography
of the dental arch. J. Shimizu Stud 1933;10:13 ( in
Japanese).
2. Numata H, A trial on the narrow beam radiography.
J. Shimizu Stud 1934;12:6 (in Japanese).
3. Paatero Y. V. A New radiographic method in dentistry.
Svom Hammaslaak Toimi 1946; 87:37 (Finnish).
4. Hudson D.C. Kumpala J. W. Dickson G. A panoramic
X ray dental machine. U S Armed Forces Med J.
1957;13:46.
5. Blackman S. Panoramic tomography. Dental Pract
1955;5:368.
6. Blackman S. Rotational tomography of the face. Br J
Radiol. 1960 Jul;33:408-418.
7. Fromer, Stabulas – Savage, Radiology for Dental
Professionals: 8th edition: 260, 264.
†
Alderson Research Laboratories, NY.
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C. Pravda et al.
8. A.F.Markus, D.I. Poswillo, J. Semple. The Reverse
panoral radiograph. Br Dent J. 1987;162(4):145-148.
9. Williams F.R, Hudson F.R, Markus A. F. Rotational
panoramic radiography – a comparison of radiation
doses in the standard and reverse positions ( unpublished
data).
10. Bartolla A, Calenda E, Calcichia A, Indovina P.L. Dental
orthopaantomography : survey of patient dose.
Radiology 1983;146:821-823.
11. Wall BF, Fisher ES, Paynter R, Hudson A, Bird PD.
Doses to patients from pantomographic and conventional
dental radiography. Br J Radiol. 1979;52:727-
734.
Correspondence :
Dr. C. Pravda M.D.S
Reader
Department of Oral Medicine and Radiology, Sathyabama University Dental College & Hospital
Jeppiaar nagar, Old Mamallapuram Road, Chennai – 600 119
EMAIL: prabhakaranramachandran@yahoo.co.in
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