1. The Bisecting Technique

2. Principles of Bisecting:
Bisecting is based on the simple geometric rule of isometry, which states two triangles are equal if they have two equal angles and share a common side.

3. Bisecting Angle
The film must be placed along the lingual surface of the tooth.
The point where the film contacts the tooth, and the plane of the film form an angle.
The dental radiographer must visualize a plane that bisects, or divides in half, the angle that is formed by the tooth and film.

5. Principles of Bisecting, con’t
The dental radiographer must then direct the central beam perpendicular (90 degrees) to that imaginary bisector.
When the central beam is perpendicular to that bisector, two imaginary congruent triangles are formed
When these principles are followed strictly, the tooth image is accurate.

6. Bisecting Angle Technique

7. Film Holding Devices:
Film holders are recommended so the patient does not have to hold the film themselves.
This reduces patient exposure, and the possibility that the film might shift around when being held in place by the patient’s finger.

8. Film Holding Devices
Some film holding devices used for bisecting angle technique are:
Rinn BAI instrument:
works like XCP, except it is designed for the film to be placed closer to tooth surface
Stabe
Snap-A-Ray

9. Finger Holding Method:
Used as an alternative when a film holding device is not possible
Problems include:
The patient’s finger or thumb is used to stabilize the film (placed behind the film and teeth)
The patient’s hand is usually in the path of the x-ray beam, resulting in unnecessary exposure

10. Finger Holding Method
The patient may bend the film, causing distortion
The patient may not hold the film with enough pressure, causing it to slip
Without the use of a beam alignment device, cone cut occurs more readily

11. Finger Holding Method

12. Why do we use the Bisecting Technique?
When dealing with a patient who has difficult or unusual anatomy
When the patient has a disabling condition that may prevent them from closing on a bite block
When dealing with an uncooperative patient, such a small child
Used with certain endodontic films

13. Guidelines for Vertical Angulation in Bisecting Angle Technique

14. Review Bisecting:
Number of films and groups of teeth are generally the same as paralleling, but generally only #2 size film is used in ALL exposures.
Horizontal angle is the same as paralleling
Film should extend 1/8 – ¼ inch beyond the incisal or occlusal edge
Vertical angle is determined by the imaginary bisector