Radiographic techniques Flashcards
What affects the quality of a radiographic image?
- the relationship of the x-ray source, object and receptor
What are the 3 intra oral radiographs?
- peri-apical
- bitewing: horizontal and vertical
- occlusal: maxilla and mandible
what are the 5 most common extra oral radiographs?
- Dental panoramic tomogram (DPT)
- Lateral cephalogram
- Posterio-anterior mandible
- lateral oblique mandible
- occipto-mental views of facial bone
What os a peri-apical radiograph?
- x-ray shows from the crown of tooth to the root and surrounding bone, also shows between teeth
what is a horizontal and vertical bitewing radiograph?
- horizontal bitewing: shows crown of tooth and bone levels, doesn’t show entire root
- aim to see from distal edge of 4 to medial edge of 8 - approx. 3 teeth - vertical bitewing: shows crown of tooth and more bone but not entire root
- good for identifying inter proximal caries and alveolar bone crest
what is occlusal radiograph?
- maxillary occlusal: shows anterior part of maxilla and teeth
- Submandibular occlusal: shows: shows floor of mouth and mandibular teeth
What is a DPT radiograph? what are other alternative names for a DPT?
- X-ray tube rotates around the patient’s head with a constant long exposure of 14 seconds forming a panoramic view image of teeth and supporting structure.
- OPT/ OPG: orthopantomography
What is an advantage and disadvantage of a DPT?
- adv: tolerable by patients
- disadvantage: body shape can man positioning difficult
What is an advantage and disadvantage of a DPT?
- adv: tolerable by patients
- disadvantage: body shape can man positioning difficult
What is a lateral cephalogram? When is it commonly used?
- radiograph taken from a lateral side of the head, used to show the relationship between teeth to the jaws and the mandible to the rest of the facial skeleton - orthodontists
- Image also shows the soft tissue pattern of the nose and lips - useful in surgical planning
what is a postero-anterior mandible view? what is it useful for? Why is it key to take two views at right angle to each other in fractures?
- PA mandible is used to show fracture of mandible (must be used alongside DPT)
- To show full extent of fracture: must take two views at right angle to each other
What is a lateral oblique mandible?
- view taken of mandible and maxilla from the side
- commonly used for children in hospital that can’t tolerate bitewing
- can be used for mandibular fracture if DPT not available
- useful in showing the buccal teeth both erupted and unerupted
- useful in showing position of unerupted third molars
what is occipto-mental views of facial bones?
- OM views of face most. commonly done as first form of diagnosis when patients report facial trauma in A&E
- shows fractures of orbits, maxilla and zygomatic arches
- two views taken: first beam is angled at 10 degrees and second beam angled 30 degrees
why is it useful to take OM radiographs whilst standing?
- helps show fluid levels in the antra (cavity e.g. maxillary sinus)
What affects the details shown in an image?
- how close the receptor is to the image
What are the main clinical indications for use of peri-apical radiographs?
- detection of apical infection or inflammation
- detailed evaluation of apical cysts and other lesions within the bone
- assessment of periodontal status - bone resorption
- after trauma to the teeth and associated bone
- assessment of root morphology before extraction
- assessment of presence and position of unerupted teeth
- during Endodontics
- pre-operative assessment and post-operative appraisal of apical surgery
- evaluation of implants postoperatively
What are the two most important radipgrahic techniques?
- paralleling technique
- bisected angle technique
What is the difference between the two techniques: paralleling and bisected angle technique?
Paralleling
- uses a holder to facilitate the positioning
- the holder keeps receptor parallel to the tooth and x-ray beam
- an accurate reproducible image
bisected angle
- can be done without holder, making it easier for patient
- technique is operator dependent so each Time it will be done slightly different meaning image is not reproducible
which technique is the technique of choice ?
- paralleling
Describe the position of the holder in relation to the teeth and x-ray source in paralleling technique.
- Receptor parallel to the tooth
- x-ray beam is perpendicular to tooth/receptor
explain why a holder is useful in paralleling technique.
- it minimises magnification of object to the film so gives an accurate reproducible image
what is the downside of the paralleling technique
- holder is bulky and patient may not tolerate it
we have different types of holders, what are the 3 main components of every holder?
- a bite block - keeps receptor in place
- a metal arm/rod - fits into the bite block
- locator ring - slides onto the metal arm, allows the collimator to align with receptor
In DDH, the holder used has 4 colors: blue, yellow, red and green. what are they each for?
- Blue: anterior teeth
- Yellow: posterior teeth
- Red: bitewings
- Green: Endodontics procedures
what is computed radiology?
- When the type of receptor used is a phosphor plate, this is processed, erased and reused
what is digital radiology?
- conventional film with chemical processing
The relationship of receptor to tooth affects final image, describe the position of receptor in relation to the tooth.
- the vertical plane of the film should be parallel to long axis of the tooth
- horizontal plane of film must be parallel to dental arch
if an image produced has elongated roots, what is the issue with the technique?
- The receptor and tooth are not parallel vertically
if teeth appear overlapped, what is the problem with technique?
- the horizontal plane of film is not parallel to dental arch (difficult around 3 and 4’s due to bending of arch)
another variable affecting image geometry is direction of X-ray beam to receptor an teeth. what must the position of beam be in?
- beam must be perpendicular to receptor and tooth
what mistake in the position of x-ray beam causes elongation of teeth in the image?
- the x-ray beam is angled too much upwards
what mistake in the position of x-ray beam cause foreshortening of teeth in the image? (makes them look short and stubby)
- x-ray beam positioned too downwards
what affects horizontal angulation of x-ray beam and what mistake occurs in the final image?
- the ring must fit in the correct position on metal arm
- the beam has a rectangle collimator that must fit the ring
- this ensures the beam is in the correct position horizontally
- if beam position horizontal is wrong, it will make the teeth overlapped in the image
what do we mean by magnification in radiology?
- how much larger the size of object under investigation is compared to the object’s size in real life
what two factors affect image size (magnification)?
- the distance of the x-ray source to the receptor
2. the distance between receptor and object
The source to object distance must be long, explain why?
- x-ray beam spreads out in all directions and continues to spread as it passes through the object and makes the object appear larger on receptor
- increasing distance between source and object ensures the beam diverges less and image is more accurate in size
the receptor to object distance must be short, explain why?
- it reduces the time the beam has to diverge and magnify the image after passing through the image.
what should the image receptor orientation be for posterior teeth and anterior teeth?
- film should be landscape for posterior teeth and horizontal bitewings
- portrait for anterior teeth and vertical bitewings
what causes cone cutting as shown in image ?
- caused when the corners of collimator haven’t touched guiding ring and absorbed radiation, preventing receptor being exposed and forming the image
what are some barriers to good position of x-ray?
- mouth size
- gag reflec
- film size
- digital sensor shape and size
- patient in pain etc.
what are the 4 most common receptor sizes?
- 0, 1, 2 and 4
what size do we use for anterior teeth in adults ? (periapical)
- size 0 or 1
- can use size 2 for bisected angle technique
what size do we use for posterior teeth in adults ? (periapical)
- always size 2
what size do we use for children anterior teeth? (periapical)
- size 0
what size do we use for children’s deciduous posterior teeth? (periapical)
- size 0
what size do we use for children posterior permanent teeth? (periapical)
- size 2
What size do we use for horizontal and vertical bitewings in adults?
- 2 only
what size do we use for horizontal and vertical bitewings in children?
- children under 10: 0 or 1
- children over 10: size 2
why is there a dot/ small circle on radiographs? where should this dot be positioned?
- the receptor has a radiopaque mark which should always be positioned to the crown of the tooth
- it indicates whether image is right or left
- on bitewing, dot should always be placed next to the palate
