Introduction to Dental Radiology

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Introduction to Dental Radiology

• Dr. FJ Owotade.

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Historical Perspectives

• In late 1895, a German physicist, W.C. Roentgen
  was working with a cathode ray tube in his
  laboratory, when he accidentally discovered x
  rays.
• Roentgen found that the X-ray would pass through
  the tissue of humans leaving the bones and metals
  visible. One of Roentgens first experiments late
  in 1895 was a film of his wife Bertha's hand with
  a ring on her finger.
• The news of Roentgens discovery spread quickly
  throughout the world.

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Wilhelm Conrad Roentgen.
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• In July 1896, Dr. C.E. Kells became the first man
  in the world to hold a dental clinic (held in
  Asheville, N.C.) using an X-ray machine .
• His story as recounted by Buddy Stall is attached
  as an appendix.

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The radiographic image.

• Radiographs often referred to as the clinicians
  main diagnostic aid.
• Understanding the radiographic image is central
  to radiology.
• The image is produced by x-rays passing through
  an object and interacting with the photographic
  emulsion on a film.
• The extent to which the emulsion is blackened
  depends on the no of x-rays reaching the film
  which depends on the density of the object.

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• The final image can be described as a 2-D picture
  made up of a variety of black, white and grey
  superimposed shadows referred to as a shadowgraph
  or radiograph.
• Understanding the nature of the shadowgraph and
  interpreting the information requires a knowledge
  of the following.
• The radiographic shadow.
• The 3-D anatomical tissues.
• The limitations imposed by a 2-D picture and
  superimposition.

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The radiographic shadow

• The white or radiopaque shadows on a film
  represents the various dense structures in the
  object which have totally stopped the x-ray beam.
• The black or radiolucent shadows represents areas
  where the x-rays passed through the object and
  has not been stopped at all.
• The grey shadows represent areas where the x-ray
  beam has been stopped to a varying degree.

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The final shadow of any object is thus affected
by

• The specific type of material of which the object
  is made.
• The thickness or density of the material.
• The shape of the object.
• The intensity of the x-ray beam used.
• The position of the object in relation to the
  x-ray beam and the film.
• The sensitivity of the film.

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The 3-D anatomical tissues.

• A sound anatomical knowledge is a prerequisite
  for radiological interpretation.
• When viewing a 2-D radiographic image, the 3-D
  anatomy responsible for the image must be
  considered.

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The limitations imposed by a 2-D picture and
superimposition.

• The main limitation of viewing the 2-D image of a
  3-D object are.
• Appreciating the overall shape of the object.
• Superimposition and assessing the location and
  shape of structures within an object.
• To appreciate the overall shape of the object, it
  must be viewed from several different positions.

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Postioning the Film, Object and X-ray beam.

• The position of the x-ray beam, object and film
  needs to satisfy certain basic geometrical
  requirements. These include
• The object and the film should be in contact or
  as close as possible.
• The object and the film should be parallel to one
  another.
• The xray tube head should be positioned so that
  the beam meets both the object and the film at
  right angles.

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X-ray beam characteristics.

• The ideal x-ray beam for imaging should be
• Sufficiently penetrating, to pass through the
  patient and react with the film emulsion and to
  produce good contrast between the different
  shadows.
• Parallel (non divergent) to prevent magnification
  of the image.
• Produced from a point source to reduce blurring
  of the edges of the image (Penumbra effect).