Extra oral radiography Flashcards
Purposes of extra-oral radiography?
To view non dento-alveolar structures
Pt can’t tolerate intra oral
Image larger sections of dentition
View maxillary mandibular relationship for ortho
Give some names of extra oral radiographs
Panoramic
Cephalometric - lateral, posterior-anterior
Oblique lateral
Skull
What do true and oblique mean?
true = perpendicular to head
Oblique = angled
What reference lines can be used for positioning extra oral radiographs?
mid sagittal plane - line down centre of face
Interpupillary line - connects both pupils
Frankfort plane - superior EAM and inferior orbital margin
Orbitomeatal line - centre of EAM and outer canthus
What is cephalometry? Clinical applications?
The measurement and study of the head
Orthodontics
- Monitor changes over time
what can be seen in a lateral cephalogram?
Teeth
Facial bones and soft tissues
Paranasal sinuses
Cervical vertebrae
Pharyngeal soft tissues
Label the structures
Purple = sinuses
Blue = nasal bones
Yellow = anterior and posterior nasal spine
Green = sella turcica
Pink = soft palate
Red = posterior wall of nasopharynx
Orange = hyoid bone
What orthodontic uses do lateral cephalograms have?
Assess skeletal discrepancy
Aid in locating unerupted, malformed or misplaced teeth
Indicates upper incisor root length
What is used to make sure patients head remains in the correct position for a cephalogram? What does it do
Cephalostat
Holds head correct angle
Prevents head movement
Establishes correct distance between x-ray focal spot, patient and receptor
How far away should the receptor be from the focal spot?
1.5-1.8m
How can soft tissues be made to be viewed more clearly on the radiograph?
Place aluminium wedge filter in the unit to attenuate the area of beam exposing facial soft tissues
Use software to enhance soft tissues
How is radiation dose limited in lateral cephalograms?
Triangular collumation
- This reduces exposure to the cranium
Thyroid collar also used
- to protect radiosensitive thyroid gland
What are benefits/cons of oblique lateral cephalograms?
No superimposition of the opposing side
Difficult to master technique so usually superseded by panoramic
When may one wish to use oblique lateral cephalograms?
When intra-oral or panoramic contraindicated
- poor cooperation children
- involuntary movements
Assessment of pathology
Presence of unerupted teeth
View mandibular fractures
Evaluate lesions affecting jaws
