Dental Panoramic Radiography

• When taking a DPT, the x-ray source fires through the object to the receptor around centre of rotation.

  
• CBCT = cone beam CT - a 3D panoramic imaging device - much cleaner than conventional DPT.

  Clean because v thin focal trough (0.4mm) - focal trough for conventional DPT = up to 3cm in posterior mandible.

  CBCT has a much higher radiation dose too, so not primarily used.

  
• Effective dose comparison:

  • Full mouth periapicals - 150 uSv
  • DPT - 15-20 uSv

  
• Schematic representation of the radiological anatomy of the maxilla and mandible.

  
• Selectrion criteria for DPTs may include:

  • Orthodontic assessment (dental tissues only)
  • Bony lesions
  • Pre-GA - often in children so that patient doesn't go for surgery and have things missed
  • Periodontal disease (orthogonal program)
  • 3rd molars/IDC (relationship to inferior dental canal)
  • Trauma - mandibular fractures
  • Pre-implant planning (CBCT more often now)
  • Cannot tolerate intra-oral views
• The problem with this DPT is that there is no separation of teeth - the pt did not use a bite block.

  
• The problem with this DPT is that the teeth are overlapping. This limits the diagnostic yield.

  
• The problem with this DPT is that the head is too far forwards - this is a common error. As a result, too much spine is seen in the image, and the anterior teeth appear very thin and elongated.

  
• The problem with this DPT is that the head is too far back - there is no spine on the image, and the anterior teeth are very large. This happens because they are too far from the image receptor.

  
• The problem with this DPT is that the pt is too far back in the machine and has their chin up - this means that the smile line is lost.

  
• The problem with this DPT is that the teeth are magnified on the right compared to the left - this happens because they are further from the film, since the pt is looking to the right side. The left maxillary sinus appears denser too - this is not pathology, it's just an artefact due to pt rotation.

  
• In this sectional DPT looking at the TMJ area, the ramus of the mandible is magnified on the RHS due to pt rotation in that direction.

  
• In this DPT, the pt has tilted their head to the side, causing a shift in the angulation of the image.

  
• In this DPT, the pt has moved whilst the radiograph was being taken - this is most commonly seen in elderly and children.

  
• Ghost images:

  • The dotted line below outlines the shape of the ghost image of the left side of the mandible. Because it is very dense bone, this normal anatomy can produce a ghost image.
  • Ghost images are areas of the image that have been degraded due to the overlapping of the objects from the contralateral side, which are out of focus. Eg left side of mandible, which is in focus, is projected onto right side of mandible, as a larger image, which is not sharp and above the real image of the mandible.
  • Little can be done about this.

  
• Ghost images:

  • Metallic artefacts can create ghost images - eg earrings

  Shown here, earrings (hoops) are magnified and reflected onto the opposite side

  
• A ghost image will be:

  • Located on the opposite side from the image of the actual object
  • The same shape as the actual object
  • Larger than the image of the actual object
  • Projected higher on the film
  • Less distinct (less sharpness; "ghostlike")
  • Located on the opposite side from the image of the actual object
  • The same shape as the actual object
  • Larger than the image of the actual object
  • Projected higher on the film
  • Less distinct (less sharpness; "ghostlike")
• DPTs can be used to assess edentulous jaws - can assess retained roots that may be causing problems - can find IDC (runs high in this patient) because may be subject to pressure from a denture, which would be uncomfortable.

  
• DPTs can be used to check for malignancy - deep periodontal pockets found here - prematurely erupting 8 too (when you see prematurely erupting teeth in children, it's a red flag, so further investigation should take place) - patient ended up having leukaemia in this case

  
• With a digital DPT, the same technical anomalies can occur:

  • Nose stud has been left in - potential metal artefact
  • Quite a lot of spine showing too - so patient probably far forwards in machine
  • Shadow of tongue visible too; tongue not placed on rough of mouth to allow tooth roots to be seen more easily

  
• Use 60kV instead of 70 to see soft tissues.

  
• If object magnified and unsharp at periphery, likely to be at a distance from the film.