The Bisecting Technique

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.

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.

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.

Bisecting Angle Technique

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.

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

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

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

Finger Holding Method

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

Guidelines for Vertical Angulation in Bisecting Angle Technique

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