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Validity of cephalometrics

  • Magnification:
      • It occurs because x ray beams are not parallel with all points on the object to be examined .
      • The use of long focus object and short object film distance have been recommended in order to minimize such projection errors (Franklin 1952)
      • Focus film distance > 280 cms doesn’t alter magnitude of projection error (Ahlquvist et al 1986)
      • Enlargement compensation for lateral ceph. Radiograph is 4.6 to 7.2 % & for frontal film 0.3 to 9.2 % at 60” anode to midsaggital plane distance (Bergersen O E 1980)
  • Geometrically constructed landmarks and landmarks identified as points of change between convexity and concavity often prove to be very unreliable
  • Rad. Complexity of the region makes it difficult to locate landmarks
  • Baumrind and Frantz pointed out: errors in landmark location is a function of 3 variables

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