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

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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 136
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. 137
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REVERSE OPG - A REVIVAL. C. Pravda, D. Koteeswaran. - Aosr.co.in

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