occlusal radiography Flashcards
how are occlusal radiographs taken
- image receptor in occlusal plane
what size is image receptor
- 7x5cm
- can get smaller for smaller mouths and children
what is a oblique radiograph like
- similar to a large periapical but more teeth
when are oblique occlusal taken
- can’t open mouth
- when periapicals are not possible
- pathology too large to be seen on periapical = but nowadays would just use CBCT
- less painful for those with trauma
- localisation using parallax (along with panoramic, other occlusal, or periapical)
what do circular radiolucencies often have
- often contain cysts
what is the ideal projection geometry
- image receptor and object in contact and parallel
- parallel beam of x-rays
- x-ray beam perpendicular to object plane and image receptors
why do you never get the image size the same as the objext
- due to divergent beam
what are problems with projection geometry
- image receptor and object no in contact
- beam of x-rays not parallel
- x-ray beam central ray may or may not be perpendicular to object plane and image receptor
- image size not identical to object size due to magnification = divergent beam
what are the solutions to projection geometry problems
- bisecting angle technique
what is the bisecting angle technique
- image receptor and object partly in contact but not parallel
- image receptor and object close together at crowns, but apart at apices
- still use long FSD for machines working at 60kV and over
how does the angle affect the image in bisecting angle technique
- if x-ray beam at 90 degrees to long axis of tooth = elongated image
- if x-ray beam at 90 degrees to plane of image receptor = short image (foreshortened)
- neither of these are ideal
what is the correct vertical angle
- x-ray beam at 90 degrees to line bisecting angle formed by long axis of tooth and plane of image receptor
- image receptor positioned with 2-3mm beyond tooth edge
- vertical angle judged by eye
- adjust angle to adapt to incisor angulation = proclined then increase, retroclined then decrease
how does oblique occlusal require head position to be
- need occlusal plane (of the jaw being examined) to be horizontal
- want head in a standardised position = different for upper and lower
how is the head placed in correct position for oblique occlusal
- use soft tissue points
- maxilla
= ala-tragus line horizontal (fleshy bit of side of nose, to the ear, lateral border of nose opening to auditory meatus) - mandible
= corner of mouth-tragus line
= slightly tip head back
what are storage phosphor plates
- multi use sensors
- protected by plastic cover
- protected from tooth marks by cardboard or plastic
how are storage phosphor pates used
- insert into plastic so writing can be seen through clear side =seal
- black side of cover must face x-ray source
- go between upper and lower and held in place by patient biting
- slide in so dot goes in first
- active surface is pale blue
- open end is outside patients mouth
- hold it against the teeth you are x-raying
how do you ensure the sensor is kept in the correct position
- patient to bite gently to hold protected sensor still
- watch them to ensure no chewing action
- plastic protectors can be used as an alternative to card
- check tube head from 2 angles
what are the centring points for periapical
- maxilla = on ala-tragus line
- mandible = 1cm above lower border of mandible
what the centring points for oblique occlusals
- maxilla = 1cm above ala-tragus line
- mandible = through lower border of mandible
what should the horizontal angle always be
- 90 degrees to the teeth being examined
what are guideline vertical angles for oblique occlusals
- Upper anterior (standard) - 60º
- Upper occlusal centred on canine - 55º
- Upper occlusal centred on premolar - 50º
- Upper occlusal centred on molar - 45º
- Lower anterior occlusal - 40º to occlusal plane
- Lower occlusal centred laterally - 35º to occlusal plane
- drops by 5 as move back in arch, larger angle makes teeth shorter
summary of oblique occlusal
- bisecting angle technique used
- standardised head position
- mid-sagittal plane perpendicular to floor
- occlusal plane correct for arch
- image receptor in occlusal plane, active surface towards teeth
- orientation of image receptors dependent on size of mouth and patient tolerance - long axis front to back probably most comfortable
what is true/cross-sectional occlusal radiography
- occlusal size image receptor of periapical size
- plan view when beam is through long axis of a tooth
- only do in lower
what are the indications to do a mandibular true occlusal
- detection of submandibular duct calculi
- assessment of buck-lingual position of unerupted teeth
- evaluation of pathological bucco-lingual expansion
- horizontal displacement of fractures
- CBCT may be used nowadays if available
why do we not use mandibular true occlusal often
- mainly just use CBCT
how can submandibular duct calculi grow
- concentric growth
- conforms to duct
what are ‘kissing teeth’
- teeth which are close together and need to be treated together
- facing each other in radiograph
how is mandibular true occlusal done
- image receptor transverse in occlusal plane OR lengthwise over region of interst
- head tipped as far back as comfortable
- x-ray beam directed at 90 degrees to image receptor in midline OR through region of interest
- only thing we can move is patient’s head
- image receptor at different angles depending on the angle, and X-ray tube is then placed on chest facing upwards
