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### Bisecting angle technique

# Bisecting angle technique is based on:
A. ALARA principle
B. SLOB Technique
C. Rule of Isometry
D. Convergence

The correct answer is C. Rule of Isometry.

The Bisecting angle technique is based on a simple geometric theorem, Cieszynski's rule of Isometry, which states that two triangles are equal when they share one complete side and have two equal angle.

Position of the film as close as possible to the lingual surface of the teeth, resting in the palate or on the floor of the mouth.

The plane of the film and the long axis of the teeth form an angle with its apex at the point where the film is in contact with the teeth.

Construct an imaginary line that bisects this angle and direct the central ray of the beam at right angles to this bisector.

This forms two triangles with two equal angles and  a common side. (the imaginary bisector)

Several methods can be used to support films intra orally for Bisecting angle projections.

The preferred method is to use a film holding instrument (e.g. The Snap-A-Ray) or Bisecting angle instrument. Both provide an external device for localizing the X ray beam.