BDS3 Radiology Flashcards
(37 cards)
What are the two different techniques for taking a PA?
Parallelling technique
Bisecting angle technique
When might you need to use the bisecting angle technique?
If you cannot get the receptor parallel to the tooth.
Young children struggling tot tolerate the receptor
Shallow hard palate or lingual sulcus
Tender tooth preventing patient fighting on toecpeot holder.
Edentulous patient.
Describe the process of taking a PA with the bisecting angle technique.
Place receptor as close to the subject as possible.
Estimate the angle between the long axis of the tooth and the receptor.
Bisect the angle with an imaginary line.
Aim the x-ray beam perpendicular to this bisecting line.
What angle is an anterior oblique maxillary occlusal radiograph taken at?
65 degrees to the receptor.
Why might you take an anterior maxillary occlusal radiograph?
Unerupted/ectopic teeth
Trauma cases
What angle is a true occlusal radiograph taken at?
90 degrees
What circumstances might you take a true mandibular occlusal radiograph?
Sialolith in submandibular duct
Bucco-lingual expansion of mandible
Describe the different occlusal radiographs that you can take.
Anterior oblique maxillary occlusal
Lateral oblique maxillary occlusal
Anterior oblique mandibular occlusal
True mandibular occlusal
How does cervical burnout occur?
Triangular shaped radiolucency at the neck of the tooth.
Occurs because of the different radio density of the tooth in different areas.
- the x-ray beam is less attenuated in this area compared to the rest of the crown.
- At contact points, there is less tooth structure for the x-ray beam to pass through, less attenuation and so darker area.
What is the Mach band effect?
Optical illusion caused by the retina.
human eye makes the bright areas look brighter and dark look darker.
- Can make the human eye think there is a radiolucency under a restoration but it is not caries.
- The radiolucency will look more linear and straight cut- caries does not present itself like that.
What is the Y of Ennis?
Where the maxillary sinus meets the nasal cavity.
What is the focal trough?
Tomographic slice of interest.
- structures outside the focal trough will appear faint and out of focus.
Anything within the focal trough will appear sharp.
Why is it not uncommon for incisors to appear blurry on an OPT?
Focal trough is thinner in this region
- because of the speed of rotation at this point.
What are the limitations of the focal trough?
Ectopic teeth outwith the focal trough may appear blurry.
Certain malocclusions that make it difficult for the patient to bite down on the bite peg may be out of focus.
How do structures appear on the radiograph that a re buccal or lingual to the focal trough?
If the person is lingual to the focal trough- appear magnified (wider).
If the person is Bucal to the focal trough- appears narrower.
What are the advantages and disadvantages of OPT compared to PA?
Advantages
- Can capture entire dentition in one image
- Able to view non-dental structures
- No intra-oral holders, easier for the patient.
Disadvantages-
- higher radiation dose
- Higher exposure time- patient must tay still for longer
- Worse clarity- lower spatial resolution, more superimposition, more artefacts.
What is field limitation?
Minimising the area that the image takes- reduces the dosage.
What must you get the patient to do before placing them in the OPT machine?
Remove any dentures or URA.
Remove all jewellery in the head and neck
Remove glasses, hairclips.
What reference lines are used for OPT?
Frankfurt plane
Mid-sagittal plane
Canine line
What do you advise the patient before you leave the room for an OPT?
Hold on to the rails
Stay still
Roll tongue to roof of the mouth
Do not swallow
How do ghost shadows appear on an OPT?
Transposed to the opposite side
Higher up
Magnified
Blurry
How do double shadows form?
Structures that are close to the centre of rotation due to their central position, get captured twice.
Cervical spine
Hyoid bone
Soft palate
Under what circumstances might you take an OPT?
Periodontal bone levels
Grossly neglected dentition
Assessment of third molars prior to surgical intervention
Part of h orthodontic assessment
Unerupted tooth that couldn’t be captured using intra-oral techniques.
In a hospital setting
- Maxillary sinus pathology
- Mandibular fracture
- Pre-implant planning
What are the basic principles of the ICPR system with regards to all radiation exposures?
Justified- must do more good than harm
Optimised- ALARP
Limited- System of individual radiation dose limits to prevent unacceptable levels of exposure.
- For staff and not patients.
