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The Bisecting Technique

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.

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The Bisecting Technique

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  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.

  4. 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.

  5. Bisecting Angle Technique

  6. 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.

  7. 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

  8. 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

  9. 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

  10. Finger Holding Method

  11. 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

  12. Guidelines for Vertical Angulation in Bisecting Angle Technique

  13. 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

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