Panoramic radiography l Oral radiology MCQs for dental students

 Panoramic radiographic technique (Orthopantomography) l Oral radiology MCQs for dental students 

Important points to remember in orthopantomography (panoramic radiography)

1. Panoramic radiographic technique is also known as pantomography and rotational panoramic radiography.
2. Indication: To evaluate overall health of maxillofacial structures, know exact location of third molar if it is horizontally impacted and cannot be seen on periapical radiography, and evaluate developmental anomalies.
3. Advantages: It provides broad anatomical coverage of maxillofacial structures while radiation dose to the patient is also considered to be low. It is a reliable screening tool and is an effective patient education tool.
4. Limitations: Relatively high initial setup cost of the system, which may be two to four times that of an intraoral X-ray generator. Superimposition, magnification, geometric distortion and overlapping of structure are other disadvantages of this technique, as the ghost of the cervical spine can obscure area of interest, particularly in the lower anterior region.
5. Image formation: The concepts of panoramic image formation have been described by earlier researchers in mid- 1900s. This technique utilises a narrow vertical negatively angled beam. The angle can be −4 to −7°. Because of the negative vertical angulation, the beam exposes the patient just below the occipital bone.
6. Zone of sharpness: The zone of sharpness (also known as image layer) is a three-dimensional curved zone in which the objects are reasonably well defined on the panoramic image. Image layer is also known as the focal trough.
7. Patient positioning guidelines: Usually the following three reference laser lights are present on the panoramic machines: Frankfort plane light, canine light and midsagittal plane light. The Frankfort plane is parallel to the floor, the midsagittal plane of the patient’s face is perpendicular to the floor and the canine light is aligned with the mesial contact of the maxillary canine.
8. Too far forward or too far back: If teeth are too far forward to the focal trough towards the film, the resultant image of the teeth will show horizontal minification.
9. Patient’s chin tilted too high or too low: Occlusal plane appears flat or reversed. There may be superimposition of the hard palate on the apices of the upper anterior teeth.