1. Radiology – Paralleling, Bisecting, Bitewing
Chapters 17, 18, 19
Radiology – Paralleling, Bisecting, Bitewing

2. Chapter 17 - Paralleling
Paralleling Technique- Also known as the extension cone paralleling technique (XCP)

3. Chapter 17 – Principles of Paralleling technique
Everything lines up to long axis
Film is placed parallel to long axis of tooth being radiographed
Central ray is perpendicular or at a right angle to the film and long axis of the tooth

4. Parallelism
Achieve parallelism between film & tooth – Film must be placed away from the tooth and toward middle of mouth.
Increase the object to film distance to keep film parallel with long axis of tooth – increased object to film distance = more magnification

5. Parallelism Increased magnification causes loss of definition
To compensate increase the target film distance (16” PID)

6. Advantages Accuracy- Produces an image that has dimensional accuracy
Simplicity- Use of the film holder and beam alignment device elminates guessing placement
Duplication- It is easy to standardize and can be accurately duplicated

7. Disadvantages
Film placement- difficulties may be encountered w/ children or w/ adult patients who have a small mouth or shallow palate
Discomfort- the XCP may impinge on the oral tissues and cause discomfort for the patient

8. Chapter 18 Bisceting Technique
Also called the bisecting angle technique, bisection of the angle technique, and short- cone technique
Another method used to expose periapical films

9. Bisecting the Angle
Bisecting the angle between film & tooth – rule of isometry.
Based on two imaginary equal triangles

10. Bisecting the Angle Film placed along the lingual
Point where film contacts the tooth – the film and the long axis of the tooth form an angle.
Visualize a line that divides in half (bisects) the angle formed by the film & long axis of tooth. Line = imaginary bisector
Not good for pt. w/bone loss – distorts level of bone

11. Angulation of PID
Angulation of the PID is critical with the bisecting technique
Angulation is used to describe the alignment of the CR on the horizontal and vertical planes
This is important with the snap-a-ray or finger holding method

12. Rules for bisecting technique
Film placement
Film position
Vertical angulation
Horizontal angulation
Film exposure

13. Advantages
Can be used w/o a film holder when the anatomy of the patient precludes the use of a film-holding device
Decreased exposure time, a 8” PID is preferred with the bisecting technique

14. Disadvantages
Image distortion- occurs when a short PID is used, it causes image magnification
Angulation problems- w/o a film holder and aiming ring visualizing the imaginary bisector can be difficult, image may result in distortion
Unnecessary exposure- with the finger holding method the patient’s hand is unnecessarily exposed to the primary beam

15. Chapter 19 bitewing technique
Also know as the interproximal technique
Method used to examine the interproximal surfaces of the teeth

16. Bitewing aka Interproximal
Used to diagnose caries between the teeth and bone levels

17. Bitewings – 5 Basic Rules
Film placement – teeth to be examined
Film position – parallel to crowns of both arches
Vertical angulation – central ray of beam directed through contact areas
Horizontal angulation – central ray of beam through contact areas
Film exposure – beam centered on film so all areas are exposed – failure – cone cut or partial image