Lecture 3 Physics

• What is the most important factor in imaging geometry?

  Plate and object parallel to each other
• Minimal 4mm bone level and crowns should be seen on a ...

  bitewing
• Bitewings should see the distal surface of..

  the last standing molar

  last interproximal space
• Blip on film is important because:

  Anatomical marker

  Legal requirement

  Right or left?
• Bitewings the blip should be

  mesially
• for PAs the blip should be

  towards the crown
• Angle of radiograph may not be correct if

  The teeth are not in profile
• PA 3mm from bite surface to edge of the film

  True or False

  True
• If Frankfurt's plane is horizontal


  you see a single line on an xray
• Head moves away from plate


  image is bigger
• head moves closer to plate


  image is smaller
• characteristic of xrays relevant to dentistry:

  • travel in straight lines
  • obeys inverse square law
  • travels speed of light
  • penetrates matter
  • exites and ionises atoms
  • produces chemical, biological, photographic, fluoroscopic effects
• how are xrays produced:

  • cloud of electrons at filament are accelerated to tungsten target
  • hit target, penetrate surface, energy lost
  • produced photons of xrays, 1-5% efficient
• radiography: the process or occupation of taking radiographs to assist in medical examinations.
• radiology: the science dealing with X-rays and other high-energy radiation, especially the use of such radiation for the diagnosis and treatment of disease.
• xray examination requirements:

  • source of xray - tube
  • subject - pt
  • recording system - film, digital sensor, phosphor plate
• image formation?

  • film/phosphor plate behind enamel will be hit with very few photons and appear white/clear on final image
  • part lying under pulp will be hit with many photons and will appear black/dark grey