6 - Extra-oral radiography Flashcards
What is the purpose of extra-oral radiography?
- larger section dentition
- alternative if patient cannot tolerate intraoral
- non-dentoalveolar regions
What are different types of extra-oral radiography?
- panoramic
- cephalometric
- oblique lateral
- skull radiograph
Define a lateral radiograph.
X-ray beam aimed at the side of the head
Define a postero-anterior radiograph.
Beam starts posteriorly passing anteriorly
Define a true radiograph.
Angulation of beam is perpendicular to head
Define an oblique radiograph.
Angulation of beam is not perpendicular to head
What is the Frankfort plane?
Line between infraorbital margin and superior border of external auditory meatus
What is the orbitomeatal line?
Line that connects the outer canthus to centre of EAM
Define cephalometry.
- measurement and study of the head
- used in orthodontics and orthognathic surgery
- based on reproducible radiographs
What anatomy can be observed on a lateral cephalogram?
- teeth
- facial bones and soft tissues
- paranasal sinuses
- pharyngeal soft tissue
- cervical vertebrae
What are lateral cephs used for in orthodontics?
- assessing skeletal imbalance for functional/fixed appliances when moving teeth labio-lingulally
- to locate unerupted/malformed teeth
- indication of upper incisor root length
What is a cephalostat?
- ensures reproducible images
- ear rods and forehead support ensure the same head position in every image
- establishes correct distance between receptor and patient
What distance should be the receptor be from the x-ray focal spot?
1.5m-1.8m
How can soft tissues be better visualised on lateral cephs?
- aluminium wedge filter placed in unit to attenuate specific area of beam
- use software to enhance soft tissues
What is the standard lateral ceph dimensions?
17cm, reduced height
