Extra-oral Radiography Flashcards
What are the purposes of extra-oral radiography?
Imaging larger sections of the dentition
Alternative when patient unable to tolerate intra-oral radiography
Imaging non-dentoalveolar regions
What are the common types of extra-oral radiographs?
Panoramic radiographs
Cephalometric radiographs - lateral or postero-anterior
Oblique lateral radiographs
Skull radiographs - occipitomental, postero-anterior skull/,mandible, Reverse Towne’s, true lateral
What lines and planes are commonly used in extra-oral radiographs?
Mid-sagittal plane - line down middle of face
Interpupillary line - connects both pupils
Frankfort plane - connects infraorbital margina and superior border of EAM
Orbitomeatal line - connects outer canthus and centre of EAM
What is the difference between the Frankfort plane and Orbitomeatal line?
10º
When is cephalometry used?
Orthodontics and orthognathic surgery
Often used to monitor changes over time
What is most important in cephalometry?
Radiographs must be standardised and reproducible - need consistent images between dentists/centres and over time
What is the main anatomy in a lateral cephalogram?
Teeth
Facial bones and soft tissues
Paranasal sinuses
Pharyngeal soft tissue
Cervical vertebrae
When are lateral cephalograms used in orthodontics?
Assessing skeletal discrepancy when functional appliances or fixed appliances are to be used for labio-lingual movement of the incisors
Aiding localisation and assessment of unerupted, malformed or misplaced teeth
Giving an indication of upper incisor root length
At what stages of orthodontic treatment are lateral cephalograms used?
Diagnosis
Tx planning
Monitoring progress (of tx or patient development)
Appraisal of treatment results
What is a cephalostat?
Ensures standardised positioning of equiptment and patient’s head
Avoids discrepancies between radiographs taken years apart by different staff
Reduces magnification/distortion of an image
What are the functions of a cephalostat?
Holds head at correct angle
Stabilises head to prevent movement
Establishes correct distances between X-ray focal spot, patient and receptor
What is the standard distances for a lateral cephalogram?
Receptor should be 1.5m - 1.8m from the X-ray focal spot to minimise magnification
How can soft tissues be seen better in extra-oral radiography?
- Place an aluminium edge filter in the unit to attenuate the specific area of the beam exposing the facial soft tissues
- Use software to enhance the soft tissues post-exposure
Describe patient contact shielding
A thyroid collar is almost always used as the thyroid gland is relatively radiosensitive
This may obscure the hyoid bone and cervical vertebrae
What is CBCT?
Cone-beam computed tomography
Proved a cross-sectional 3D image but at an increased radiation dose
