Extra-oral Radiography Including Cephalograms Flashcards
1
Q
What are the purposes of extra-oral radiography?
A
- imaging larger sections of the dentition
- alternative when patient cannot tolerate intra-oral
- imaging non-dentoalveolar regions
2
Q
What are common types of extra-oral radiographs?
A
- panoramic
- cephalometric
- lateral
- postero-anterior
- oblique lateral
- skull
- occipitomental
- postero-anterior skull/mandible
- reverse Towne’s
- true lateral
3
Q
What are reference lines and planes used for?
A
- anatomical landmarks used to aid positioning of extra-oral radiographs
4
Q
What is the midsagittal plane?
A
- line down middle of face
5
Q
What is the interpupillary line?
A
- connecting both pupils
6
Q
What is the Frankfort plane?
A
- connects infraorbital margin and superior border of external auditory meatus
7
Q
What is the orbitomeatal line?
A
- connects outer canthus (lateral aspect of eye) and centre of external auditory meatus
8
Q
How many degrees difference is there between the Frankfort plane and the orbitomeatal line?
A
- 10 degrees
9
Q
What is cephalometry?
A
- measurement and study of the head
- different points, angles and distances
- analyse anatomy - used in:
- orthodontics
- orthognathic surgery
- monitoring changes over time - based on radiographs
- must be standardised and reproducible
10
Q
How is the head held still while taking cephalometric radiographs?
A
- ear prongs
- in patients external auditory meatus - forehead positioned
- ensure head is at correct vertical height
- prevents tilting
11
Q
What are lateral cephalograms?
A
- standardised, true lateral skull radiograph
- main anatomy
- teeth
- facial bones and soft tissues
- nasal bones
- frontal sinuses
- nasal spines
- sella turcica - pharyngeal soft tissues
- soft palate
- posterior wall of nasopharynx - cervical vertebrae
- hyoid bone
- used for:
- orthognathic planning
- orthodontic treatment
- assessing skeletal discrepancies
- assessment of unerupted/malformed/misplaced teeth
- indication of upper incisor root length
- used for diagnosis, Tx planning, progress, results
12
Q
What equipment is used to take lateral cephalograms?
A
- cephalostat
- produce standard and reproducible radiographs
- ear rods and forehead support
- head held at correct angle
- stabilises head to prevent movement
- establishes correct distance from x-ray focal spot
- can use solid state or phosphor plate receptor
- can be single or multifunctional unit
- +/- panoramic
- +/- CBCT
13
Q
What are the standardised distances for lateral cephalograms?
A
- receptor should be 1.5-1.8m from the x-ray focal spot
- minimises magnification
- if too close beam is divergent, magnifying parts of the image
- if too far photons are more parallel, less magnified image
14
Q
How can facial soft tissues be captured in lateral cephalograms?
A
- placement of aluminium wedge filter into unit
- attenuates specific area of beam exposing tissues
- use of software to enhance soft tissues post exposure
- due to the fact soft tissues show up poorly when exposure settings are optimised for hard tissue
15
Q
How is collimation used when taking cephalometric radiographs?
A
- field of view should not be bigger than what is clinically required
- reduced height, reduced width
- 17cm reduced hight most common
- 26cm, full height is largest
- triangular collimator
- not for units with solid-state sensors
- reduces exposure to cranium
