Cephalograms

Question 1

What are intensifying screens?

Answer 1

• 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

Question 2

Understanding the purpose of using intensifying screens in extraoral radiography

Answer 2

• 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

Question 3

Understanding differences between Cephalograms and Skull Views

Answer 3

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Question 4

What are the clinical indications for: Lateral cephalogram (Lat Ceph)

Answer 4

• 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

Question 5

What are the clinical indications for: Frontal Views

Answer 5

• 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)

Question 6

What are the clinical indications for: Submentovertex (SMV) Projection

Answer 6

o Zygomatic arch fractures – very good for this!!
o Thickness of body of mandible
o Skull base

Question 7

What are the clinical indications for: Water’s View

Answer 7

• 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

Question 8

What are the clinical indications for: Reverse Towne View

Answer 8

• Condylar neck fractures
• TM Joint disorder

Question 9

What are the clinical indications for: Lateral Oblique (or Oblique Lateral) Radiograph

Answer 9

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Question 10

What are the general indications for extra-oral radiography?

Answer 10

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

Question 11

What are the 3 layers of the intensifying screens?

Answer 11

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

1. 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
2. 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.
3. 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

Question 12

What speed of intensifying is used in extra oral radiography?

Answer 12

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