Orthodontic Radiology Flashcards
How is dose kept ALARP?
Equipment – correct operation and maintenance
Adequate staff training
Justification – only take radiographs when required and select the most appropriate view
What is the effective dose in mSv for different dental radiographs?
IO = 0.0003-0.022
OPT = 0.0028-0.038
Upper standard occlusal = 0.008
Lateral Ceph = 0.0022-0.0056
Mandible/maxilla CT = 0.25-1.4
Dentoalveolar CBCT = 0.01-0.67
Craniofacial CBCT = 0.03-1.1
What is the estimated risk of developing fatal cancer for different dental radiographs?
IO- 1 in 10,000,000
OPT- 1 in 1,000,000
Upper standard occlusal- 1 in 2,500,000
Lateral Ceph- 1 in 5,000,000
Mandible and maxilla CT- 1 in 14,300 to 80,000
Dentoalveolar CBCT- 1 in 30,000 to 2,000,000
Craniofacial CBCT- 1 in 18,200 to 670,000
What can be done to limit dose?
70kV
Rectangular collimation
F speed film/digital receptors
What are the reasons for taking an OPT in new orthodontic patients at the assessment?
- 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
What are the other indications for an OPT?
Oral surgery
- pathological jaw lesions
- surgery
- evaluation and review
- trauma /fractures
What are the stages in reporting an OPT?
Check patient details and check orientation of film
Chart teeth : start from the back of mouth
-> Identify erupted teeth/ unerupted teeth/ any missing teeth/ any extra teeth
Check roots of teeth – apical pathology/ root resorption
Check state of tooth crowns Any obvious caries? /large restorations/ hypoplasia
Check for any alveolar bone loss
Any other findings- cysts
Lastly focussing on reason you took radiograph
What are the causes of faults when taking an OPT?
Due to the limitations in the width of the focal trough – particularly at the front of the mouth
Faults in patient positioning- use guidelines
Movement of patient- exposure takes 18-20 secs, patient may not remain still
What happens if structure is outwit the focal trough?
It will be blurred or not visible at all
What is the issue with focal trough and malocclusions?
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 teeth, may end up outwith the focal trough
How do different malocclusions affect image? (teeth are outwith focal trough)
Class II div I - 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 patient is too far forward in OPT machine?
The teeth will look narrower on the film (in anterior region)
- 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 patient is too far back in 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 is required to produce a clear image?
The speed of the x-ray beam through the teeth and the speed of the receptor through the x-ray beam need to be synchronised
Why are ghost images always higher up?
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 objects can appear as ghost images?
Metal objects
Restorations
Earrings
Normal anatomic features
What happens if patient moves during OPT exposure?
Gross distortion
What happens if we take an OPT with Frankfort plane angles down?
Smiley face appearance
What are the reasons for taking a standard upper occlusal?
To look for pathology in the upper anterior region of the maxilla
To confirm the presence of unerupted teeth
Root resorption – but periapical view better for assessment
To aid localisation of unerupted teeth in combination with another radiographic view (parallax)
What are the reasons for taking a periapical radiograph?
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 are the reasons for taking bitewings?
To assess caries status
To provide more information on tooth prognosis
To get more information on alveolar bone levels
What are the types of parallax and how are they achieved?
Vertical- OPT and Upper maxillary occlusal
Horizontal- 2 PAs
How is parallax applied?
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 x-ray beam
What are the indications for taking a lateral ceph?
To aid diagnosis
-> Skeletal class II or III (marked AP discrepancy)
-> Vertical discrepancy
Treatment planning
-> Help clarify the tooth movements to be achieved
-> To decide orthodontics only or orthognathic surgery
-> Orthognathic planning
Progress monitoring
-> Fixed appliance treatment
-> Functional appliance treatment
-> Monitoring facial growth
-> Predict future growth?
What is position is Lateral Ceph taken in?
Cephalostat
Frankfort plane- horizontal
Teeth in RCP
What are the important reference lines for lateral ceph?
Sella-nasion (and how it relates to A and B point)
Frankfort plane
Maxillary plane
Occlusal line
Mandibular plane
What are examples of different analysis forms in lateral ceph radiographs?
Eastman
Downs
Rickets
Jacobson
What are the different ANB (AP discrepancy) values for different severity of malocculsion?
> 8- severe class II
6-8- Moderate class II
4-6- mild class II
2-4- Class I
0-2- Mild class III
-3-0- Moderate class III
<-3- Severe class III
What should the angle of upper incisors to maxillary plane be on a ceph? (Ui/MxP)
109 +/- 6
What should angle of lower incisors to maxillary plane be on a ceph? (Li/MnP)
93 +/-6
What should the angle created by relationship of upper and lower incisors be? (Ui/Li)
135 +/- 10
What are the different values of MMPA for different types of vertical discrepancy?
> 37- severely increased face height
32-37- moderately increased face height
27-32- mildly increased face height
27- average
22-27- mildly decreased
17-22- moderately decreased
<17- severely decreased
What errors can occur in cephalometry?
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 structures may be superimposed on ceph image?
Anterior wall of sella
Middle cranial fossa
Anterior surface of zygomatic process
Outline of IAN canal
Anterior border of chin
Inner cortical plate at mandibular symphysis
What are the uses of cone beam computer tomography?
Localisation of teeth- if we need more info on proximity to adjacent teeth/structures (may cause resorption)
To get better view of structural anamolies
-> Gemination
-> fusion
-> supernumeraries
Some orthognathic cases
Some cleft palate cases
Why is CBCT not used often in ortho?
Radiation dose is much higher than plain films
Longer exposure/Patient set up time takes longer than OPTs
Additional training needed to report on CBCT
Cost
