Extra-oral Radiography

Question 1

Images relating to the mandible?

Images relating to the maxilla and cranium?

Answer 1

Images relating to mandible:

• postero-anterior mandible
• lateral oblique mandible
• DPT

Images relating to maxilla and cranium:

• lateral cephalogram
• occipito-mental views
• sailography

Question 2

Describe some positioning landmarks:

Answer 2

• radiographic baseline: line from outer canthus of eye to external auditory meatus (EAM) - represents base of skull
• frankfort plane: inferior orbital border to upper border of EAM - aka anthropological base line (used in DPT)
• maxillary occlusal plane: ala of nose to tragus of ear - used in CBCT

Question 3

Answer 3

Question 4

What is an anti-scatter grid?

Answer 4

Anti-scatter grid:

• stop photons scattered in patient reaching film
• avoids degrading and reducing contrast
• narrow strips of lead alternating with plastic
• fixed or moving

Question 5

List some things to consider when positioning a patient for an extra-oral radiograph:

Answer 5

• position of patient relative to film
• position of x-ray beam relative to patient
• angle of x-ray beam relative to film

Question 6

Indications for a postero-anterior mandible view?

Why is this method preferred?

Answer 6

Postero-anterior view:

• fractured mandible - shows medio-lateral displacement
• cysts and malignancy causing medio-lateral expansion or bone destruction
• good visualisation of posterior belly and ramus
• limited visualisation of head/neck of condyle
• midline can be obscured by spine
• usually requested in conjunction with a DPT
• reduced magnification of facial structures
• reduced dose to eyes

Question 7

How should a patient be positioned for a PA mandible view?

Answer 7

• pt faces film
• nose and forehead touches film holder
• radiographic base line - horizontal
• aim centre of beam at midline of pt at mid ramus height

Question 8

Indications for lateral oblique jaw radiography?

Answer 8

• fracture of body, ramus and condyle
• pathology e.g. cysts
• assessment of wisdom teeth (always request a DPT first)
• dental assessment in special needs patients
• caries in children who cannot tolerate BWs

Question 9

What are the three techniques used to take a lateral oblique jaw radiograph?

Answer 9

• isocentric positioning using a skull unit
• dental tube with vertical angulation
• dental tube with horizontal angulation

Question 10

Indications for cephalometric radiography and some points regarding the images:

Answer 10

• orthodontic assessment
• pre-orthognathic surgery
• can only be done using cephalostat
• pt positioned with rods in ears to gove standardised positioning
• image must be reproducible
• must have means of calculating amount of magnification or calibrating the digital image
• must be able to visualise soft and hard tissues

Question 11

How can soft tissues be imaged on a lateral cephalogram?

Answer 11

Aluminium filter:

• positioned over anterior part of face
• designed to attenuate the beam in anterior facial region
• allows visalisation of bone and soft tissue on one film, despite relatively high exposure factors needed for the facial bones
• if digital, tissues made visible by software

Question 12

Indications for occipito-mental views:

Answer 12

• facial bone fractures - zygoma, le-fort fractures and orbital blowout
• pathology - limited use in sinus disease, only used rarely
• different angulations allow us to view different areas of complex anatomy: OM 0, 10 and 30 most common