Chapters 17, 18, 19

1. 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