2. Extraoral Radio Flashcards
Types of extraoral radiography?
- Panoramic
- Lateral cephalometry
Panoramic radiography is also known as..
- DPT (dental panoramic tomography)
- OPG (orthopantomogram)
What are the indications for DPT/OPG?
- Overall evaluation of dentition
- Demonstrating extensive caries or periodontal disease
- Evaluating position of impacted teeth & assc vital structures e.g. wisdom teeth
- Monitoring growth & development/dental eruption
- Evaluating developmental disturbances of maxillofacial skeleton
- Assessing dentomaxillafacial trauma
- Evaluation of intraosseous pathology such as cysts, tumors or infections
- Gross evaluation of TMJ
Steps to patient preparation for DPT/OPG:
- Remove anything that has metal e.g. earrings, glasses, jewellery, dentures, hair pins
- Female patients: pregnant?
- Explain procedure to patient
- Lead apron (no thyroid collar)
Steps to equipment preparation for DPT/OPG:
- Place plastic over incisor bite-stick
- Set exposure factors (panoramic machines usually have a patient jaw size setting)
Steps to patient positioning:
- Hold onto stabilising handles
- Bite upper & lower incisors edge-to-edge into incisor bitestick, chin resting on chin support
- Immobilise head using temple support
- Use light beam markers to ensure that:
- mid-sagittal plane: vertical & centred
- frankfurt plane: horizontal (parallel to pupillary line infraorbital, inline w external auditory meatus)
- canine light - Instruct px to close lips, put tongue to roof of mouth & not move during procedure
- make sure patient is standing straight, not hunched over
- lead apron is not up to high and blocking xrays
Steps after exposure of DPT/OPG:
- Release temple support
- Remove lead apron
- Ask px remove plastic barrier
- Wipe down equipment & discard gloves
Principles of DPT/OPG:
- X-ray source & image receptor located across each other, move clockwise synchronously
-
Centre of rotation continuously moving, not fixed => produce U-shaped image layer, conforms to shape of jaws
- structures within image layer/focal trough appear well-defined & sharp
- centre of rotation contains teeth & supporting bone - X-ray beam collimated to narrow beam at source & receptor => only one part of receptor exposed at one time
- film shifts so that image captured is at a diff part of the film
Name some sources of imaging errors in DPT/OPG..
- Inherent sources
- Patient preparation
- Patient positioning
Name the inherent sources of imaging errors in DPT/OPG:
- Magnification & distortion
- Ghost and double images
Name the sources of imaging errors that can occur due to incorrect patient preparation in DPT/OPG:
- Artefacts (jewellery, glasses, dentures, thyroid collar)
- Palatoglossal airway space
Name the sources of imaging errors that can occur due to incorrect patient positioning in DPT/OPG:
- Too far backward
- Too far forward
- Chin tilting downward
- Chin tilting upward
- Rotation
- Movement
How does magnification occur in X-ray taking? Implications?
The closer the object to x-ray source, the more magnified it becomes
Implications:
- results in greater magnification/distortion in anterior region for DPT
- measurements are unreliable
What are the 2 types of magnification/distortion that can occur in DPT/OPG?
- Vertical
- upward angulation of beam, magnifies the vertical axis
- structure on lingual surface: projected higher on image
- structures on buccal surface: projected lower on image - Horizontal
- due to patient anatomy (jaw is wider or narrower than standard)
- incorrect px positioning
Ghost images, compared to real images are..
- Of same morphology
- Located on opposite side of image, higher up
- more blurred & larger
- Usually more posterior than real image
E.g. mandibular ramus, hyoid bone, impacted teeth, artefacts
Name some common double images:
- usually midline objects
- Hyoid bone
- Cervical spine
- Hard palate
- Epiglottis
What does palatoglossal airway space look like on the DPT/OPG?
- dark shadow btw hard palate & tongue
- appears over max teeth => hinder diagnosis of apical regions
- due to px not putting tongue to roof of mouth
=> imaging error due to incorrect patient preparation
DPT/OPG mandible has a V-shape, exaggerated smile appearance, what kind of patient positioning error?
Chin tilting down
- lower incisors blurry
- mandible has V-shape
- exaggerated smile appearance
- condyles at top of image
DPT/OPG mandible looks broad & flat, what kind of patient positioning error?
Chin tilting up
- upper incisors blurry
- mandible broad & flat
- ‘reverse smile’, flat occlusal surface
- condyles at bottom edge of image
What happens when patient is positioned too far behind?
- closer to source => magnification
- anterior teeth magnified => blurry & wide
- condyles close to edge of film + increased ghosting of mandible
What happens when patient is positioned too far forward?
- further from source => minification
- anterior teeth minified => blurry, small & narrow
- spine visible on both sides
Patient is rotated to one side while taking DPT/OPG, how to detect which side patient is rotated to?
- side that is larger => closer to source, magnification
- compare size of ramus of mandible!!
How long is the exposure time for DPT/OPG?
15 secs
- tell patient and make sure that px doesnt move!
- if patient moves, results in step defects + parts of radiograph appears blurred
What are the pros of DPT/OPG?
Advantages:
1. Provides overview of upper & lower jaws & all teeth
2. Ability to compare left & right sides simultaneously
3. Ease of technique
4. Quick & convenient process
5. Can use for pxs that are intolerable to intraoral radiographs
6. Useful as px education tool
7. Radiation dose lower than FMX (full-mouth series) of intraoral films
