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Chapters 17, 18, 19. Radiology – Paralleling, Bisecting, Bitewing. Chapter 17 - Paralleling. Paralleling Technique- Also known as the extension cone paralleling technique (XCP). Chapter 17 – Principles of Paralleling technique. Everything lines up to long axis - PowerPoint PPT Presentation
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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
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