ORTHOPANTOMOGRAPHY

August 31, 2024
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TOPIC: ORTHOPANTOMOGRAPHY

🌟 IMPORTANT POINTS TO REMEMBER

🔹Panoramic radiographic technique is also known as pantomography and rotational panoramic radiography.

🔹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.

🔹Advantages: It provides broad anatomical coverage of maxillofacial structures while the radiation dose to the patient is also considered to be low. It is a reliable screening tool and an effective patient education tool.

🔹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 areas of interest, particularly in the lower anterior region.

🔹Image formation: The concepts of panoramic image formation have been described by earlier researchers in the 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.

🔹Zone of sharpness: The zone of sharpness (also known as the image layer) is a three-dimensional curved zone in which the objects are reasonably well-defined on the panoramic image. The image layer is also known as the focal trough.

🔹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.

🔹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.

🔹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.

🔹Tongue not raised against the palate: There will be a radiolucent shadow superimposed over the roots of the maxillary teeth.

🔹Patient’s head rotated or wrong midsagittal plane alignment: The resultant panoramic radiograph will have asymmetry and distortion. In such a case, structures on one side will be magnified and contacts may be overlapped.

🔹Patient slumping error: Cervical spine in the midline, superimposed over the anterior teeth.

🔹Patient movement during exposure: This motion can result in blurred structures and distortion of structures, especially the areas in the path of the beam when the movement occurred.

🔹Lead apron too high: Radiopaque shadow in the midline.

🔹Earrings and neck chains not removed: Earrings are often a cause of ghost image formation and obscuring information.

📌 MULTIPLE CHOICE QUESTIONS (MCQs)

💡Panoramic radiography helps to visualise

  1. The entire dentition and surrounding alveolar bone
  2. Maxilla and mandible
  3. Sinuses and TMJ
  4. All of the above

Answer: 4

💡Which of the following statements is true for zone of sharpness?

  1. It is a three-dimensional curved zone in which objects are reasonably well-defined.
  2. It is also known as the image layer and focal trough.
  3. Objects within are relatively well-defined, whereas structures outside the focal trough may be magnified, blurred or distorted.
  4. All of the above.

Answer: 4

💡Advantages of panoramic radiography are

  1. Broad anatomical coverage and can be used for screening and as an education tool
  2. Low radiation dose
  3. Short imaging time
  4. All of the above

Answer: 4

💡Disadvantages of panoramic radiography are

  1. High initial setup cost
  2. Low resolution compared to intraoral radiography
  3. Superimposition, magnification, geometric distortion, positioning errors and ghost images
  4. All of the above

Answer: 4

💡Patient’s skin radiation exposure from single panoramic film, when rare earth intensifying screens are used, is

  1. Approximately equivalent to four bitewing radiographs using E-speed film
  2. Equivalent to a full-mouth intraoral periapical radiograph set
  3. More than an extraoral cephalometric radiograph
  4. None of the above

Answer: 1

💡The software packages provided by digital machines (using CCD or PSP) offer processing advantages, such as

  1. Contrast and brightness
  2. Zoom
  3. DICOM format
  4. All of the above

Answer: 4

💡 The shape and width of the focal trough depend on

  1. Speed of image receptor
  2. X-ray tube head
  3. X-ray beam collimator width and alignment of an X-ray beam
  4. Distance between centre of rotation and central plane of image layers
  5. All of the above

Answer: 5

💡Reference laser light present on the panoramic machine is

  1. Frankfort plane light
  2. Canine light
  3. Midsagittal plane light
  4. All of the above

Answer: 4

💡In panoramic radiography

  1. Film and X-ray tube head move in the same direction
  2. X-ray tube head and film move in opposite directions to one another
  3. The X-ray tube is stationary and the film carrier rotates around it
  4. The film carrier is stationary and the X-ray tube head rotates around it

Answer: 2

💡Thyroid collar is not recommended in OPG because

  1. It blocks X-ray beams and obscures information
  2. Low radiation dose is directed to the thyroid
  3. The X-ray beam is not directed at the thyroid gland
  4. All of the above

Answer: 1

💡In OPG

  1. Some part of film is exposed to X-ray beam at one time
  2. Circular rotational movement with a single centre of rotation produces a curved circular focal trough
  3. Structure within focal trough produces well-defined 
  4. All of the above

Answer : 4

💡Digital panoramic systems

  1. Have a lower resolution than film-based system
  2. Work on different principle from conventional films
  3. Allow image to be acquired and viewed in real time
  4. Take very less time in processing

Answer: 3

💡Static electricity seen on OPG has

  1. Tree branches appearance
  2. Radiolucent dots
  3. Lightening-like streaks
  4. All of the above

Answer: 3

💡If the image of the palate in OPG is prominent and obscures the apices of maxillary teeth, the patient is positioned

  1. With chin raised too high
  2. With chin raised too low
  3. Too far forward
  4. Too far backward
  5. None of the above

Answer: 1

💡Centres of rotation present in the latest OPG machine are

  1. One
  2. Two
  3. Multiple
  4. None of the above

Answer : 3

💡Ghost images in OPG are produced when structures

  1. Lie in front of the rotation centre
  2. Fall in rotation centre
  3. Lie behind the rotation centre
  4. Do not produce a real image

Answer : 3

💡The ghost image of the corresponding real image is usually

  1. Above the real image
  2. On the contralateral side of the real image
  3. Larger than the real image
  4. Fuzzier than the real image
  5. All of the above

Answer: 5

Oral Medicine and Radiology