Extra-Oral Views Flashcards
Which three extra-oral images relating to the mandible are regularly seen?
posterior-anterior mandible
Lateral oblique of mandible
DPT
Which three extra-oral images relating to the maxilla and cranium are regularly seen?
Lateral cephalogram (skull)
Occipito-mental views (face)
Sailography
What does an ‘oblique’ angle mean?
Neither parallel nor at right angles to a specified or implies line: slanting
What does ‘PA’ stand for?
Postero-anterior
What does ‘AP’ stand for?
Antero-posterior
What does ‘OM’ stand for?
Occipito-mental
What are positioning landmarks?
A series of imaginary lines on the side of a patient’s face which are used to help position a patient for extra-oral radiography
Name the three main positioning landmarks
Radiographic base line
Frankfort plane
Maxillary occlusal plane
Name the three main positioning landmarks
Radiographic base line
Frankfort plane
Maxillary occlusal plane
Which positioning landmark matches the description below?
Line from outer canthus of the eye to the external auditory meatus, representing the base of the skull.
Radiographic base line
Which positioning landmark matches the description below?
Line from the ala of the nose to the tragus of the ear. This landmark is used a lot in cone beam CT.
Maxillary occlusal plane
Which positioning landmark matches the description below?
Line from the inferior orbital border to the upper border of the external acoustic meatus. Can also be known as the anthropological base line.
Frankfort plane
which positioning landmark is most often used when taking a DPT?
Frankfort plane
What are the components of equipment required for an extra-oral radiograph to be taken?
Skull unit or cephalometric unit
Image receptor
Anti-scatter grid
Lateral cephalogram unit
what does scatter of x-ray photons do to the final image?
Degrade or fog the image
What is an anti-scatter grid?
A grid made up of narrow strips of lead alternating with plastic, which limits the amount of scattered radiation reaching the detector/film
Why might a PA mandible be requested?
To look for potential fractures, cysts or malignancy causing medio-lateral displacement, expansion to bone destruction.
what extra oral radiograph is a PA mandible almost always requested alongside?
A DPT
What are the two main advantages of having a PA mandible taken over other extra-oral views?
reduced magnification of facial structures on receptor
reduced dose of radiation to eyes
How would a patient be positioned in regards to equipment if a PA mandible is to be taken?
patient faces film
nose and forehead touch film holder
radiographic baseline should be 90 degrees to film
How do we find the ‘mid-line’ of the patient anteriorly and posteriorly?
Anterior: generally between the eyes
Posterior: at the external occipital protuberance
Why would we not just take a lateral mandible to visualise the mandible?
Because the two halves of the mandible will be superimposed
what way should you oblique the mandible in order to achieve full separation of the rami on the radiograph?
Oblique in the vertical plane
what are the indications for taking a lateral oblique mandible?
fracture
pathology
assessment of wisdom teeth
dental assessment in special needs patients
caries in children who can’t tolerate bitewing
What are the two techniques used to take lateral oblique mandibles?
Isocentric positioning using a skull unit
Dental tube with either vertical or horizontal angulation
What is an isocentric technique?
Where all beams used in a radiation treatment have a common focus point, a.k.a the isocenter
What extra- oral view can be tricky to take on individuals with broad shoulders and why?
Isocentric view,
The skull unit is required to be angled at 25 degrees so that the x-ray tube moves towards the patients shoulder. If shoulders are broad they can get in the way of the beam.
What are the two disadvantages of vertical angulation of the dental tube when taking lateral oblique mandibles?
Angulation can cause vertical distortion of the teeth
Maxillary teeth are not always shown clearly
What angulation of the dental tube is most common when taking a lateral oblique mandible?
Horizontal or vertical?
Horizontal
Which angulation of the dental tube when taking a lateral oblique mandible, aims through the radiographic keyhole?
Vertical or horizontal?
Horizontal
what is the radiographic keyhole?
The triangular space between the back of the ramus and the cervical spine
What is the disadvantage of horizontal angulation of the dental tube when taking lateral oblique mandibles?
X-ray beam may not pass directly between the contact points of the teeth therefore causing them to be overlapped on the film
What is a standardised and reproducible form of skull radiography in orthodontics, to assess the relationship of the teeth to the jaws, and the jaws to the rest of the facial skeleton?
Cephalometric radiography
What are the two main indications of cephalometric radiography?
Orthodontic assessment
Pre-orthodontic surgery
In a lateral ceph where is the x-ray beam aimed?
At the external acoustic meatus
what is a thyroid shield and what is it used for?
Lead collar that wraps around your neck to block the radiation that’s generated when taking a radiograph
What does a magnification rod, found in ceph films, allow for and why is it necessary?
Allows for the calculation of any magnification that has occurred on the final image and is necessary for surgical planning
The exposure required to penetrate a lateral face/skull is so great, in normal circumstances the beam would not be attenuated at all by the soft tissues, so they would not be visible on the image. What can be used to overcome this and allow soft tissues to be visualised on a lateral ceph?
An aluminium filter
What are the main indications for x-raying facial bones?
trauma and suspected fracture
pathology
what are the most common fractures to the facial bone?
Zygoma, le fort and orbital blowout
what are the three different angles of occipito-mental views used to view different areas of complex facial bone anatomy?
OM 0 degrees
OM 10 degrees
OM 30 degrees
What view is taken for imaging of facial bones?
Occipito-mental views
What should the radiographic baseline to film angle be for OM views?
45 degrees to film
What is caudal angulation?
How you would raise the x-ray tube to angle the central ray
What are the two main benefits of increasing angulation on OM views?
Projects dense bones of skull base down and away from facial structures
Improves view of zygomatic arch
when wanting to visualise the zygomatic arches, which OM view is the best to use?
OM 30 degrees
What does a star on a radiographic image indicate?
There is a fracture indicated by radiographer who took image.
