CHAPTERS 17, 18, 19

Radiology – Paralleling, Bisecting, Bitewing

PARALLELING TECHNIQUE- ALSO KNOWN AS THE EXTENSION CONE

PARALLELING TECHNIQUE (XCP)

CHAPTER 17 - PARALLELING

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

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

PARALLELISM Increased magnification causes loss

of definition To compensate increase the target

film distance (16” PID)

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

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

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

BISECTING THE ANGLE Bisecting the angle between film &

tooth – rule of isometry. Based on two imaginary equal

triangles

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

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

RULES FOR BISECTING TECHNIQUE Film placement Film position Vertical angulation Horizontal angulation Film exposure

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

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

CHAPTER 19 BITEWING TECHNIQUE Also know as the interproximal

technique Method used to examine the

interproximal surfaces of the teeth

BITEWING AKA INTERPROXIMAL Used to diagnose caries between the

teeth and bone levels

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