Cephalograms Flashcards
What are intensifying screens?
- Used to reduce radiation exposure
- Film (AgBr) is sensitive to UV and blue light
- Intensifying screen makes the film 10-60 times more sensitive to x-rays
- Screens are placed on each side of the film (double coated film) to help increase image sharpness
Understanding the purpose of using intensifying screens in extraoral radiography
- All extra oral images have large field of views – so that many other structures also get imaged eg orbit, salivary glands, brain – far more radio sensitive than the jaws
- In order to minimise extra oral radiation dosages, intensifying screens are used
- They are Scintillators that convert xray photons into numerous light photons
- Downside of intensifying screens is that it can make the image look blurry as we are exposing the film with scattered light photons
- They are placed on each side of the double coated films to increase image sharpness
Understanding differences between Cephalograms and Skull Views
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What are the clinical indications for: Lateral cephalogram (Lat Ceph)
- Orthodontic and orthognathic assessment (pre, peri and post)
- Anteroposterior (AP) relationships between the maxilla, mandible, and cranial base
- Skeletal, dental and soft tissue relationships
- Other (less common)
- Skull bone disorder (Paget’s, Multiple myeloma, hyperparathyroidism etc.)
- Paranasal sinus diseases
- Trauma
- Cranial base and Midface
What are the clinical indications for: Frontal Views
- PA Ceph: Facial asymmetry (developmental or traumatic)
- PA Skull
- Trauma
- Paranasal sinuses
- Skull bone disorders (Paget’s disease, Multiple myeloma, and
- Hyperparathyroidism)
- PA Mandible
- Fractures (post 1/3 body, angles, rami, and low condylar necks)
What are the clinical indications for: Submentovertex (SMV) Projection
o Zygomatic arch fractures – very good for this!!
o Thickness of body of mandible
o Skull base
What are the clinical indications for: Water’s View
• Paranasal sinuses (maxillary, frontal, and ethmoid).
o If assessing the sphenoid sinus, image needs to be taken with mouth open.
• Midface fractures (Le Fort I/II/III, zygomatic complex, naso-ethmoidal complex, and orbital blow-out)
o If midface fracture is suspected. Both standard and modified views are required for traditional imaging
What are the clinical indications for: Reverse Towne View
- Condylar neck fractures
- TM Joint disorder
What are the clinical indications for: Lateral Oblique (or Oblique Lateral) Radiograph
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What are the general indications for extra-oral radiography?
o Patient is unable to open mouth
o Severe gag reflex
o Trauma
o Impacted third molars
o Extensive jaw pathology
o TM joint assessment
o Orthodontic & orthognathic treatment planning
What are the 3 layers of the intensifying screens?
Intensifying screens have 3 different layers, most important is the phosphor layer in the middle
This layer contains numerous phosphor crystals which can be inorganic salts or rare earth elements
- Phosphor layer
• Composed of phosphor crystals
o Inorganic salts
calcium tungstate (CaWO4): blue light
lanthanum oxybromide (LaOBr): blue light
gadolinium oxysulfide (Gd2O2S): green light
o Rare earth elements
Have better light conversion efficacy – but are more expensive + harder to get
Lanthanum, gadolinium and yttrium - Base + Reflective Layer
• Base = Polyester plastic that ~0.25 mm thick (mechanical support)
• Reflective layer reflects light emitted from the phosphor layer back toward the x-ray film
• This reflective base increases the light emission of the intensifying screen but also results in image fogging “unsharpness” because of the divergence of light rays reflected back to the film. - Protective layer
• Polymer coat (≤15 μm thick) is placed over the phosphor layer to protect the phosphor and to provide a surface that can be cleaned
What speed of intensifying is used in extra oral radiography?
Screen-Film Speed
• Fast screen-films are used in dentistry (speed of 400 or more)
• They contain large phosphor crystals
o Thick
o Reduced radiation exposure
o Rapidly conversion of x-ray photons into visible light at the expense of decreased image sharpness
