Dental Radiography: Bisecting Technique

General Information

• Title: Dental Radiography: Principles and Techniques, Sixth Edition

• Authors: Joen M. Iannucci, DDS, MS; Laura Jansen Howerton, RDH, MS

• Copyright: 2022, by Elsevier Inc. All Rights Reserved.

Chapter Overview

• Chapter Title: Bisecting Technique

  • Focus on principles and techniques for dental radiography, specifically bisecting techniques applicable to periapical images.

Lesson 20.1: Film Mounting and Viewing

• Key Components:

  • Define key terms associated with the bisecting technique.

  • State the rule of isometry.

  • Enumerate the basic principles of the bisecting technique including:

    • Location of the receptor

    • Tooth

    • Imaginary bisector

    • Central ray

    • Position-indicating device (PID)

  • List beam alignment devices and receptor holders used with bisecting technique.

Technical Aspects

• Receptor Size:

  • Describe size 2 receptor used traditionally:

    • Anterior Teeth: Long portion in vertical direction

    • Posterior Teeth: Long portion in horizontal direction

• Angulation:

  • Horizontal Angulation:

    • Correct: Central ray directed perpendicular to the curvature of the arch and through contact areas of the teeth

    • Incorrect: Results in overlapped contact areas.

  • Vertical Angulation:

    • Correct: Results in radiographic image same length as the tooth

    • Incorrect: Results in images that differ from actual tooth length.

    • Foreshortened images arise from excessive vertical angulation.

    • Elongated images result from insufficient vertical angulation.

  • Recommended Vertical Angulation Ranges (Maxillary & Mandibular Teeth):

    • Canines: +45° to +55°

    • Incisors: +40° to +50° (Maxillary), -20° to -30° (Mandibular)

    • Premolars: +30° to +40° (Maxillary), -10° to -15° (Mandibular)

    • Molars: +20° to +30° (Maxillary), -5° to 0° (Mandibular)

Principles of the Bisecting Technique

• Rule of Isometry:

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

    • In dental imaging, this rule is applied to bisecting technique creating two equal imaginary triangles.

  • Technique Overview:

    • Film positioned as close to tooth as possible.

    • Angle between long axis of tooth and the plane of the receptor bisected.

    • Central ray directed perpendicular to the bisecting line, forming right triangles which are congruent.

Equipment and Patient Preparation

• Infection Control Procedures:

  • Prepare treatment area & supplies.

  • Patient seated and prepared, with lead apron and thyroid collar applied.

• Equipment Preparation:

  • Set exposure factors

  • Open the sterilized package containing any beam alignment devices.

Receptor Placement Techniques

• Anterior Exposure Sequence:

  • Start with maxillary right canine, moving to all maxillary anterior teeth, ending with maxillary left canine.

  • Transition to mandibular arch from left to right similarly, beginning with mandibular left canine.

• Posterior Exposure Sequence:

  • Start with maxillary right quadrant, then move to mandibular right quadrant, maxillary left quadrant, and finish with mandibular left quadrant.

  • In each quadrant, expose premolar receptor first, then molar receptor.

Advantages and Disadvantages of the Bisecting Technique

• Advantages:

  • Can be performed without beam alignment devices; adaptable techniques.

• Disadvantages:

  • Potential image distortion; angulation issues leading to foreshortening and elongation.

Summary of Vertical Angulation Guidelines

• Correct Vertical Angulation:

  • Ensures images are same length as the teeth.

• Incorrect Vertical Angulation:

  • Produces images that vary in dimensions leading to diagnostic inaccuracies.

Conclusion and Questions

• Ready for review and engagement with learners to ensure thorough understanding of bisecting technique and relevant radiographic principles.