ch 20: bisection of angle technique

basic concepts of bisecting technique

-Another method that can be used to expose periapical films

-Not recommended for routine use

-used in American Academy of Oral and Maxillofacial Radiology

why does the American Academy of Oral and Maxillofacial radiology use the bisecting angle technique

-accurate image

-least amount of radiation exposure

why is bisecting angle technique not recommended for routine use

-Anatomic configurations

-Bite block is painful

-Use of rubber dam

-Rinn not available

rule of isometry

Two triangles are equal if they have two equal angles and share a common side

bisecting technique

-The film must be placed along the lingual surface of the tooth

-The plane of the film and the long axis of the tooth form an angle at the point where the film contacts the tooth

-Imaginary bisector bisects the angle formed by the film and the long axis of the tooth

-The central ray is directed perpendicular to the imaginary bisector

-The two imaginary triangles that result are: right triangles and congruent

• Correspond exactly when superimposed

central ray

-direct at 90 degrees to the imaginary bisector

-perpendicular to the imaginary bisector & 2 imaginary equal triangles are formed

angulation of PID

-Angulation is critical

-The alignment the x-ray beam

• horizontal

• vertical

• Preferred method is Rinn (paralleling technique)

horizontal angulation of PID

The positioning of the tubehead and direction of the central ray in a side-to-side plane

correct horizontal angulation

The central ray is directed perpendicular to the film through the contact areas of the teeth

incorrect horizontal angulation

overlapped contact areas

vertical angulation

The positioning of the PID in a up and down plane

correct vertical angulation

Results in a radiographic image that is the same length as the tooth

incorrect vertical angulation

Results in a radiographic image that is not the same length as the tooth.

foreshortened images

results from excessive vertical angulation

elongated images

results from insufficient vertical angulation

advantages of bisecting technique

-Can be used without a Rinn

-Snapper-ray (↓ $)

disadvantages of bisecting technique

-Image distortion

-Angulation problems

-Unnecessary exposure