Chapter_018

Copyright © 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.Copyright © 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.Copyright © 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.Copyright © 2006 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Chapter 18

• Questions– What are the basic principles of the bisecting

technique?– What film holders may be used with the

bisecting technique?– What are the advantages and disadvantages

of the bisecting technique?


Dental Radiography

• Bisecting Technique– Basic concepts– Step-by-Step procedures– Advantages and Disadvantages


Introduction

• Purpose– To present basic concepts – To describe patient preparation, equipment

preparation, and film placement procedures used in the bisecting technique

– To describe the advantages and disadvantages of the bisecting technique and review helpful hints


Basic Concepts

• Bisecting technique– Another method that can be used to expose

periapical films


Terminology

• Angle

• Bisect

• Triangle

• Triangle, equilateral

• Triangle, right



Terminology

• Triangles, congruent

• Hypotenuse

• Isometry

• Long axis of the tooth

• Central ray



Principles of Bisecting Technique

• Rule of isometry– Two triangles are equal if they have two equal

angles and share a common side




Bisecting Technique• The film must be placed along the lingual

surface of the tooth• The plane of the film and the long axis of the

tooth form an angle at the point where the film contacts the tooth

• Imaginary bisector bisects the angle formed by the film and the long axis of the tooth

• The central ray is directed perpendicular to the imaginary bisector

• The two imaginary triangles that result are right triangles and congruent


Film Stabilization

• Film holders– A device used to position an intraoral film– Recommended because they eliminate the

need for the patient to stabilize the film

• Finger-holding method– Patient’s finger or thumb is used to stabilize

the periapical film


Film for Bisecting Technique

• Size 2 film used traditionally– Anterior

• Long portion in a vertical direction

– Posterior• Long portion in a horizontal direction


Angulation of Position-Indicating Device

• Angulation– The alignment of the central ray of the x-

ray beam in the horizontal and vertical planes




Horizontal Angulation

• The positioning of the tubehead and direction of the central ray in a horizontal or side-to-side plane– Correct horizontal angulation

• The central ray is directed perpendicular to the curvature of the arch and through the contact areas of the teeth

– Incorrect horizontal angulation• Overlapped contact areas




Vertical Angulation

• The positioning of the PID in a vertical or up and down plane– Correct vertical angulation

• Results in a radiographic image that is the same length as the tooth

– Incorrect vertical angulation• Results in a radiographic image that is not the

same length as the tooth



–Vertical Angulation– Foreshortened Images– Results from excessive vertical angulation

• Elongated images– Results from insufficient vertical angulation


If the vertical angulation is too steep, the image on the film is shorter than the actual tooth

Foreshortened imagesForeshortened images



If the vertical angulation is too flat, the image on the film is longer than the actual tooth

Elongated imagesElongated images



Rules for Bisecting Technique

• Film placement

• Film position

• Vertical angulation

• Horizontal angulation



• Correct and incorrect finger placement. Arrows indicate finger pressure holding film in place


Step-by-Step Procedures

• Patient Preparation

• Equipment Preparation

• Exposure Sequence for Film Placements

• Film Placement


Patient Preparation for Bisecting Technique

• Explain the radiographic procedure

• Position the patient in the chair

• Adjust the headrest

• Place and secure the lead apron with thyroid collar

• Remove all objects from the patient’s mouth


Equipment Preparation

• Set the exposure factors

• Open the sterilized package containing the film holder if film holders are used


Exposure Sequence for Film Placements

• Anterior exposure sequence– Begin with the maxillary right canine tooth

• Expose all of the maxillary anterior teeth• End with the maxillary left canine

– Move to the mandibular arch• Begin with the mandibular left canine• Expose all of the mandibular anterior teeth• Finish with the mandibular right canine





Exposure Sequence for Film Placements

• Posterior exposure sequence– Begin with the maxillary right quadrant– Move to the mandibular right quadrant – Move to the maxillary left quadrant– Finish with the mandibular left quadrant

• In each quadrant expose the premolar film first and then the molar film


Film Placement

• The specific area where the film must be positioned before exposure– Dictated by the teeth and surrounding

structures that must be included on the resultant radiograph











Film Placement

• Anterior film placement– Maxillary canine exposure– Maxillary incisor exposure– Mandibular canine exposure– Mandibular incisor exposure


Film Placement

• Posterior film placement– Maxillary premolar exposure– Maxillary molar exposure– Mandibular premolar exposure– Mandibular molar exposure


Advantages and Disadvantages

• Bisecting technique– Advantages

• Can be used without a film holder

– Disadvantages• Image distortion• Angulation problems• Unnecessary exposure


• Questions???

Documents

Chapter_018