BDS4 Seminar radiology Flashcards
why might take an OPT for ortho?
- State of development - presence or absence of permanent teeth
- Presence and position of ectopic or supernumerary teeth
- The stage of development of individual teeth
- The morphology of unerupted teeth
- State of the alveolar bone ( Periodontal disease )
- State of the teeth . Size of restorations, gross caries, periapical infection, other pathology
other indications for opt?
- pathological jaw lesions
- surgery - evaluation and review
- trauma /fractures
how can faults arise in opt?
- Due to the 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
problems with focal trough for ortho?
- class II div 1 - Roots of one or both upper and lower incisors may be blurred or not visible
- Class III – roots of upper incisors may be blurred
what happens if pt too far froward in opt?
teeth look narrower
- 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
if pt too far back in opt machine?
teeth will look wider
- 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?
- Ghost images are shadows created on the opposite side of
the OPT from the object which caused them. - They are caused by the tomographic movement of the xray 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.
- Ghost images can be caused by metal objects ,
restorations, earrings or by normal anatomic features
cause?
Patient positioned in OPT machine with Frankfort plane
tipped down – This produces a “smiley face” appearance.
cause?
Gross distortion of image due to the patient moving during
the exposure
Why do we request a standard upper occlusal view?
pathology upper anterior region
confirm unerupted teeth
Root resorption – but PA view better for assessment
To aid localisation of unerupted teeth in combination with another radiographic view (parallax)
Why might we request a periapical view?
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)
Why might we request a bitewing radiograph?
To assess caries status
To provide more information on tooth prognosis
To get more information on alveolar bone levels
localisation of unerupted teeth which radiographic views required?
OPT and AOM
= vertical parallax
Two periapical views
= horizontal parallax
how is principle parallax applied?
There must be a change in position of the X-ray
tube between the two radiographs.
beam- further away - same direct
beam - closer - opposite direction
palatal
buccal
Indications for taking a lateral ceph.
- To aid diagnosis
- Treatment planning
*Help clarify the tooth movements to be achieved - Progress monitoring
charcateristics of lateral ceph
- Standardised lateral radiographs of the face and base of skull
- Reproducible - patient positioned in a cephalostat a set distance from the cone and the film
how should be positioned for lateral ceph?
The Frankfort plane should be horizontal ( parallel to the floor) and the teeth should be in RCP
The head is correctly positioned and kept steady by contacting the soft tissues at nasion and bilaterally with the ear rods in the external auditory meatus
what is eastman analysis
- Measures the antero-posterior position of the maxilla and mandible relative to the base of skull
-SNA, SNB
what is measure of mandible maxilla
- Position of mandible relative to the maxilla
*ANB (anteroposterior)
*MMPA or FMPA (vertical)
what else do you measure with eastman
- Angulation of teeth to maxilla and mandible
*UIMxP
*LIMnP - Vertical facial proportions
*LAFH/TAFH ratio
what is ANB discrepancies?
what is vertical discrepancies?
what are dentoalveolar measurement?
what are commonly used soft tissue planes?$
what does this depict
Short facial type with reduced vertical proportions
what does this depict?
Long facial type with increased vertical proportions
what does this depict?
Acromegaly due to pituitary adenoma. Note enlarged sella turcica.
what are errors in cephalmetry?
Radiographic projection errors
* magnification
* distortion
Errors within the measuring system
* non-linear fields
Errors in landmark identification
* quality of image
* landmark definition and location* operator and registration procedure
what use CBCT in ortho?
Localisation of impacted teeth if we need more
information on their proximity to adjacent teeth and the possibility of resorption
To get a better view of structural anomalies e.g.
gemination of teeth/ fusion/ supernumeraries
Some Orthognathic cases
Some Cleft Palate cases
why don’t use cbct more?
- Radiation dose to the patient is likely to be considerably higher than when using plain films
- The patient set up time takes longer and for some machines
the exposure time is longer than an OPT so patient needs to keep still for longer - Reporting - additional training beyond BDS is required to interpret and report CBCT scans (legal requirement)
- Cost
