CH 14 Bisecting

Question 1

Introduction

Answer 1

Bisecting technique is not often recommended because images produced contain inherent dimensional distortion. Careful attention to teh steps of the technique can produce acceptable results when needed.

Question 2

Fundamentals of bisecting technique

Answer 2

Bisecting principle is applied when the image receptor is not, or cannot, be placed parallel to long axes of teeth. Children, adults who have a shallow palatial vault or a large torus present, when edentulous regions exist.

Question 3

An imaginary line bisecting the angle formed by the

Answer 3

Long axis of the tooth and the long axis of the film is the imaginary bisector between 2 isometric triangles. The x-ray beam is directed perpendicular to the imaginary bisector.

Question 4

Distances

Answer 4

Target to film shorter is better. Compensates for film not being parallel to tooth. Object to film - the receptor is close to teh tooth, so it can not be parallel to the long axis of teh tooth
Mandibular posterior can still be parallel. Other areas need the bisecting technique.

Question 5

Advantages

Answer 5

Image receptor placement may be easier with certain patients: children, adults with small oral cavities, low or shallow palatial vaults, or presence of large tori: patients with sensitive oral mucosa or hypersensitive gag reflex, edentulous region.

Short PID has potential to be easy to maneuver and stabilize

Question 6

Limitations

Answer 6

Produces images with dimensional distortion. Often superimposes adjacent structures. Estimating location of imaginary bisector requires skilled radiographer. Patient radiation dose may be increased if using short PID.

Question 7

Snap A Ray

Answer 7

Snap a ray can hold the film
The alligator jaws hold teh film tightly
With no support behind the film, the film can flex as the patient closes.
This makes it more comfortable for the patient.

Question 8

Patients’ finger for retention

Answer 8

Always use the hand opposite to the side of the mouth being radiographed. Max. Incisors- thumb
Max. Canines - thumb or index finger
Max and Mand. Posterior-index finger
Help the patient by positioning their thumb or finger where you want them to apply pressure.

Question 9

Horizontal angulaiton

Answer 9

Pass the central beam between teh target teeth. Adjust so teh line connecting the front and back edge of the pID is parallel with the line connecting the buccal surfaces of teh target teeth.

Question 10

Vertical angulation

Answer 10

You can see the film long axis, but you have to visualize the inclination of teh long axis of the tooth. Once you determine the angle, imagine the bisecting line and direct the x-ray beam at a 90 degree angle (perpendicular) to this line.

Question 11

Foreshortening

Answer 11

Too steep an angle, as in the diagram below, the image will be foreshortened or reduced in length. The PID is more parallel with the film. The angle the x-ray beam forms with the bisecting line is greater than 90degrees

Question 12

Elongation

Answer 12

Too shallow an angle- the image will be elongated or stretched out on the film. The PID is more parallel with the long axis of the tooth. The angle the x-ray beam forms with the bisecting line is less than 90 degrees.