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Dental Panoramic Tomography
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What we will cover… Indications Advantages/disadvantages
Technical principles Equipment Technique Film critique and common mistakes
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Indications Large pathologies/un-erupted teeth too big for intra-oral film Intra-orals not possible Assessment in: advanced periodontitis Extraction of wisdom teeth Orthodontics Growth and development Implants Grossly neglected mouth Trauma TMJ dysfunction
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Advantages Large area of coverage Bilateral view for comparison
Low dose Relatively simple to perform Easy to explain resultant image to patient Patient movement effects only one section Rapid assessment method
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Disadvantages Less sharp than intra-oral Magnification Distortion
Subtle pathology may be missed Magnification Distortion Sectional More complicated to interpret Ghost images produced Intensifying screens result in reduced resolution Different shaped dental arches
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Tomography
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Focal Trough ‘Narrow zone of sharp focus’
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The technical bit.. Linear tomography Rotational tomography
Flat focal trough E.g. Gas removal from kidney Rotational tomography Arc shaped focal trough 1 centre of rotation Dental panoramic tomography How do we achieve a horseshoe shape? 2+ centres of rotation
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Rotational Tomography
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Centres of rotation Dental Panoramic Tomography
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How does tomography work…
X-ray tube orbits back of head Cassette holder moves around front of face X-ray tube and cassette holder move in opposite directions Cassette moves in same direction as X-ray tube
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Focal Corridor f=height of film d=focal trough to film distance
x=height of XR beam Focal Corridor
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Explain… Why do we need a moving X-ray source?
Why does the cassette carriage move? Why does the cassette move?
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Equipment Features Tubehead Control panel Positioning apparatus
Chin support Bite rod Light beam markers Head clamps mirror Image receptor
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The Control Panel What do we need? kV, mA settings
Patient size selection Height adjustment AP bite rod adjustment (canine light) Field limitation options Range of dental arch shapes
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Light Beam Markers Mid-sagittal plane - vertical
Frankfort plane – horizontal Canine light Position between upper lateral incisor and canine
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The Image receptor
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Intensifying screens Intensifying screens convert X-ray photons to light (UV and visible) to amplify blackening effect Uses light emitted from photoelectric effect Less radiation needed to expose film
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Technique: Preparation
Load cassette and place in carriage Load cassette and place in carriage Load cassette and place in carriage Load cassette and place in carriage Load cassette and place in carriage Load cassette and place in carriage Load cassette and place in carriage Load cassette and place in carriage Load cassette and place in carriage Set exposure factors Insert bite rod/cover Set carriage to start position Remove artefacts
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Technique: Positioning
Load cassette and place in carriage Load cassette and place in carriage Guide patient into unit Load cassette and place in carriage Load cassette and place in carriage Load cassette and place in carriage Load cassette and place in carriage Load cassette and place in carriage Load cassette and place in carriage Patient holds handles Place chin on support Bite upper and lower teeth into groove on bite rod Patient stands up straight and steps forward slightly
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Technique: Positioning
Use light beam markers to check position Explain movements to patient Patient swallows and places tongue in roof of mouth Ask patient to keep still Expose
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5 8 1 7 10 4 9 2 12 11 11 3 3 6 Anatomy
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Normal Anatomy 1.Mandibular condyle 2.Angle of mandible
3.Body of mandible 4.Ramus of mandible 5.Right Orbit 6.Symphysis of mandible 7.Left maxillary sinus 8.Zygomatic arch 9.Mandibular 3rd molar 10.Ear lobe 11.Cervical spine 12.(Root of) mandibular 2nd premolar
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Film Evaluation 1. Identification 2. Anatomical marker 3. Collimation
3. Area of interest 4. Correct positioning 5. Artefacts 6. Adequate exposure factors
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Film Evaluation
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Common Problems Patient movement Ghosting Incorrect positioning
of artefacts of Cervical spine Incorrect positioning AP positioning Rotation Chin tilt Tilting
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Chin tipped down too much
V shaped smiley mandible Arching of spine Condyles high on film Hyoid bone streaked across mandible
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Chin up too high. Flattened occlusal plane Palate superimposed on roots of maxillary teeth Broad, flat mandible
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Patient twisted – right mandibular rami wider than left
Condyles assymetrical Teeth tend to be wider one side than other Too far forward on one side, too far back on the other
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Too far forward Spine superimposed over rami Blurred, narrow anterior teeth Too much spine visible on edge of film
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Too far back Ghosting of mandible and spine Condyles at very edge of film Blurred and widened anterior teeth
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Slouching
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Standing up straight
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Airway
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Underexposed
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Conventional Digital
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3d
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