Dental Radiography: Bisecting Technique

Bisecting Technique

• The bisecting technique is based on bisecting the angle formed by the long axis of the tooth and the long axis of the film.
• The x-ray beam is directed perpendicular to the bisecting angle.

Projections

• The bisecting technique uses different vertical angulation for different teeth.
• Incisors: +40 degrees for maxillary, -15 degrees for mandibular
• Canines: +45 degrees for maxillary, -20 degrees for mandibular
• Premolars: +30 degrees for maxillary, -10 degrees for mandibular
• Molars: +20 degrees for maxillary, -05 degrees for mandibular

Indications

• The bisecting technique is indicated for patients with:
  • Shallow palates
  • Palatal tori
  • Tongue tie or high lingual frenum

Advantages

• Comfort: The technique is generally comfortable for patients.
• Snap-A-Ray film holders: These holders are easy to use and accommodate film placement.

Disadvantages

• Distortion of image: The bisecting technique can result in image distortion.
• Positioning error / operator error: Proper positioning is crucial for accuracy, and errors can lead to inaccurate images.
• Film movement by patient: Patient movement can also cause image distortion.

PID Angulations: Bisecting Technique

• Horizontal angulation: Remains the same for both the bisecting and paralleling techniques.
  • The central ray is directed perpendicular to the curvature of the arch and through the contact areas of the teeth.
  • Incorrect horizontal angulation leads to overlapped contact areas, hindering examination of interproximal areas of the teeth.
• Vertical angulation: Determined by the imaginary bisector, with the central ray directed perpendicular to it.
  • Correct vertical angulation produces an image the same length as the tooth.
  • Incorrect vertical angulation leads to either elongated or foreshortened images.
    • Elongation: Occurs when vertical angulation is too flat, resulting in an image longer than the actual tooth
    • Foreshortening: Occurs when vertical angulation is too steep, resulting in an image shorter than the actual tooth.

Purpose and Use

• The bisecting technique is used to:
  • Detect incipient carious lesions in the interproximal area.
  • Detect crestal bone loss.

Bite-Wing Radiographs

• The film is positioned parallel to the crowns of both upper and lower teeth, and the central ray is directed perpendicular to the film.
• The bite-wing radiograph should include:
  • Distal half of the crowns of the cuspids
  • Both premolars
  • The first molars on both the maxillary and mandibular arches.
• The molar film should be centered over the second molars.

Object Localization

• Clark's rule / SLOB technique (Tube shift technique): A method to locate the position of a tooth or an object in the jaws.
• Right angle technique for mandible: Another method to locate objects in the jaws.