Radiology 7. Extra-oral Radiography Including Cephalograms Flashcards
what are the common types of extra-oral radiographs?
- panoramic radiographs
- cephalometric radiographs (complete side image of skull or even postero-anterior)
- oblique lateral radiographs
- skull radiographs
the term extra-oral means x-ray source & receptor OUTSIDE patient
what is the mid-sagittal plane?
line down middle of face
what is the interpupillary line?
connects both pupils
what is the frankfort plane?
connects infraorbital margin & superior border of external auditory meatus
what is the orbitomeatal line?
connects outer canthus (corner of eye near nose) & centre of External Auditory Meatus
what is cephalometry?
the measurement & study of the head using many different points, angles & distances to analyse anatomy
what are the clinical applications of cephalometry?
orthodontics & orthognathic surgery, often used to monitor changes over time
what are the main anatomy features of a lateral cephalogram?
- teeth
- facial bones & soft tissues
- paranasal sinuses
- pharyngeal soft tissue
- cervical vertebrae
what are the uses of lateral cephalograms in orthodontics?
- assessing skeletal discrepancy when functional or fixed appliances are to be used for the incisors
- aiding location & assessment of erupted, malformed, or misplaced teeth
- giving indication of upper incisor root length
what is a cephalostat, and its function?
ensures standardised positioning of equipment & patient’s head for a consistent radiograph that can be used to compare past images.
A cephalostat includes ear rods & forehead support.
Its function:
- holds head at correct angle
- stabilises head to prevent movement
- establishes correct distances between x-ray focal spot, patient & receptor
what is the standardised distance for a cephalogram?
1.5-1.8m
the x-ray focal spot from the receptor - minimises magnification. Also means futures images can be directly comparible
what patient contact shielding precautions are used during cephalometry?
thyroid collar almost always used since the thyroid gland is relatively radiosensitive
what is an oblique lateral radiograph?
provides view of posterior jaws without superimposition of contralateral side.
Its useful if the patient is unable to tolerate intra-oral radiographs & unable to stay still/fit in panoramic unit
[also uncommon nowadays]
