Orthodontic Radiology Flashcards
What is ALARP in radiation safety?
As Low As Reasonably Possible
What is Dose Limitation?
Wherever possible collimate the beam to reduce the field of view
How do you justify taking radiographs in orthodontics?
The benefit to the patient from the diagnostic information should out weigh the detriment of the exposure
To provide information on the state of the dentition
How can faults in OPT’s arise?
Limitations in the width of the focal trough- particularly at the front of the mouth
Faults in patient positioning
Movement of patient during the exposure
What is the relevance of the focal trough to malocclusion?
Anything out with the focal trough will be blurred or sometimes not visible at all
When a patient’s malocclusion does not permit them to bite edge to edge within the groove on the bite block either the whole tooth, or roots of the teeth may end up out with the focal trough
What happens if the patient is positioned too far forward in the OPT machine?
The teeth will look narrower on the film
This is because the teeth are further from the centre of rotation and the x-ray beam therefore passed more quickly through these teeth relative to the speed of the image receptor
What happens if the patient is positioned too far back in the OPT machine?
The teeth will look wider on the film
This is because the teeth are closer to the centre of rotation and the x-ray beam therefore passed more slowly through these teeth relative to the speed of the image receptor
What are ghost images?
Shadows created on the opposite side of the OPT from the object which caused them
They are caused by tomographic movement of the x-ray machine
They are always seen at a higher level on the opposite side of the mouth because the x-ray beam of the machine is angled upwards by 8 degrees
What radiographs are used in the parallax technique?
OPT and anterior occlusal maxillary= vertical parallax
Two periapical views= horizontal parallax
How is the principle of Parallax applied?
There must be a change in position of the X-ray tube between the two radiographs
Objects furthest away from the x-ray beam will move in the same direction as the beam moves
Objects closer to the x-ray beam will move in the opposite direction to which the beam moves
How do you justify bitewings?
To assess caries status
To provide more information on tooth prognosis
To get more information on alveolar bone levels
How do you justify periapicals?
To assess for root resorption
To look for evidence of periapical infection
To assess if a tooth might be ankylosed
To aid localisation of unerupted teeth in combination with another radiographic view (parallax)
What is the parallax technique used for?
To aid localisation of unerupted teeth in combination with another radiographic view
What is lateral cephalometry?
Standardised lateral radiographs of the face and base of skull
Cephalometry is the analysis and interpretation of these radiographs
What are some indications for taking a lateral ceph?
To aid diagnosis
Treatment planning
Progress monitoring
