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
What are the cons of DPT/OPG?
Limitations:
1. Lower resolution than intraoral radiographs => cannot visualise fine deetails
2. Magnification/distortion => measurements unreliabel
3. Superimposition of anatomic structure & presence of ghost & double images => interpretation is difficult
4. Structures outside of image later blurred out/not evident
5. Need accurate px positioning to avoid imaging errors
6. Difficult to image when px has skeletal discrepancies
7. Technique may not be suitable for young children (cannot stay still for 15s)
Criteria for diagnostic radiographs:
- All upper & lower teeth & supporting alveolar bone clearly seen
- Magnification in vertical & horizontal dimension equal
- Minimal ghost shadows & mandible & cervical spine
- Hard palate appear above apices of max teeth
- NO artefacts
- NO palatoglossal air space
- Equal mesio-distal widths of left & right Ms & rami (NO rotation)
- Correct labelling w px’s name (or other identification) & date of exam
- Radiograph labelling should not obscure any anatomic features
- Image marked w R/L to represent right/left sides
