Extra-oral radiography including Cephalograms Flashcards
What are the purposes of extra-oral radiographs?
- Allows for visualisation of teeth, jaws, facial bones etc
- Imaging larger sections of dentition
- Alternative when patient unable to tolerate intra-oral radiography
- Imaging non-dentoalveolar regions
What are some common types of Extra-oral radiographs?
- Panoramic
- Cephalometric (Lateral and Poserto-anterior)
- Oblique lateral
- Skull (Occipitomental, Postero-anterior skull/mandible, Reverse townes, true lateral)
How does direction of beam in relation to head equate to the names of radiographs?
- Lateral = aimed at side of head
- Postero-anterior = starting posteriorly and passing anteriorly
How does angulation of beam relate to names of radiographs?
- True = perpendicular to head
- Oblique = not perpendicular to head
Give some examples of reference lines/planes
- Mid-sagittal plane = line down middle of face
- Interpupillary line = connects both pupils
- Frankfort plane = connects infraorbital margin and superior border of EAM
- Orbitomeatal line - connects outer canthus and centre of EAM
*10° difference between orbitomeatal line and Frankfort plane
Why are reference lines/planes useful?
- Useful for comparison of radiographs before and after surgery for example
What is Cephalometry?
- The measurement and study of the head
- Uses many different points, angles and distances to analyse anatomy
- Must be standardised and reproducible as need consistent images between dentists/centres and over time
What are some clinical applications of Cephalometry?
- Orthodontics and Orthognathic surgery
- often used to monitor changes over time
What is a lateral Cephalogram?
- Standardised, true lateral skull radiograph taken using specialised equipment
What is the main anatomy covered by a true Cephalometric lateral skull radiograph?
- Teeth
- Facial bones and soft tissues
- Paranasal sinuses
- Nasal spines (anterior and Posterior)
- Pharyngeal soft tissue
- Cervical vertebrae
- Sella turcica
- Hyoid bone
How are lateral cephalograms used in orthodontics?
- Assess skeletal discrepancy when functional appliances or fixed appliance are to be used for labio-lingual movement of incisors
- Aiding location and assessment of unerupted, malformed or misplaced teeth
- Giving indication of upper incisor root length
What is the function of 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 standardised distance of lateral cephologram?
- Receptor should be 1.5m to 1.8m from x-ray focal spot to minimise magnification
- Keeping distances between focal spot, patient and receptor consistent ensures images taken at any time are directly comparable
What is collimation?
- Reducing field of view to no bigger than what is clinically required
- Units that do not use a solid state sensor should also have triangular collimation to reduce exposure of cranium
What is patient contact shielding?
- Reduces dose to patient during radiograph
- Thyroid collar almost always used as thyroid gland is relatively radiosensitive
- May obscure hyoid bone and cervical vertebrae (irrelevant to majority of cases but sometimes used to assess maturity of skeleton)
