2.4 - Occlusal Radiographs Flashcards
Where does image receptor go for occlusal radiographs?
in occlusal plane
What size image receptor do we use for adults?
Larger 7x5cm
What image receptor do we use for children?
size 2 PA 2x4cm
What are indications for occlusal radiograph?
- PA type of assessment but in a case where we can’t take a PA (For example if pt has TRISMUS so we can’t get film holder in – this is better tolerated in these pts)
- Pathology too large to be seen on a single PA
- Retained roots – when looking at something obvious an occlusal view will give us a good view
- Trauma – fractures to teeth and alveolus – this is less painful for pt as gently brings teeth together either side of the occlusal receptor rather than trying to bite hard on plastic piece of PA film holder
- Good for working out where missing structures are- Eg unerupted canines
What do oblique occlusal allow us to see?
Extent of pathology
What is ideal projection geometry?
Object and image receptor in contact and parallel
object and image same size
x-ray beam perpendicular to object plane and image receptor
What are the problems with ideal projection geometry?
• Image receptor and object NOT in contact
• beam of X-rays NOT PARALLEL – they diverge
• 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
o we increase fsd to at least 20cm to compensate for this
What is bisecting angle technique?
This is when the image receptor and object are partly in contact but not parallel (image receptor and object close contact at crown but not at apices)
In occlusal radiographs using bisecting angle technique what must the x-ray beam be?
bisecting the angle between the teeth and the receptor.
What happens if we have too little vertical angulation?
the image is elongated or stretched out on the film and angle the x-ray beam forms with bisecting line is less than 90 degrees
What happens if we have a foreshortened image?
the image is shortened or reduced in length and the angle the x-ray beam forms with the bisecting line between image receptor and object >90 degrees
What happens if the beam is at 90 degrees to image receptor in occlusal radiographs?
foreshortened image
What happens if beam is at 90 degrees to bisector?
good image using correct bisecting angle technique
What is the bisecting angle formed by?
Long axis of tooth and plane of image
How much of the image receptor should be visible beyond incisal edge?
2-3mm
If incisors are proclined what will we need to do?
increase angle
If incisors are retroclined what do we need to do?
decrease angle
What is the head position when taking oblique occlusal?
Occlusal plane of jaw being examined to be horizontal
When is occlusal plane altered?
When mouth is opened
When taking oblique occlusal of maxilla what reference plane do we use?
the ala trague line must be horizontal
What is ala tragus line?
ala of nose to tragus of the ear
When taking oblique occlusal of mandible what plane do we use?
we use the corner of mouth to tragus line horizontally - parallel to floor
What position should pts head be in for maxillary occlusal?
straight forward
What position should pts head be in for mandibular occlusal?
tilt backwards
Diff between PAs and occlusal?
Occlusal films will give much more information than bisecting angle periapicals and there is only a 5 degree difference between bisecting angle periapical and bisecting angle occlusals of the same area.
When are occlusal taken?
Occlusal films are often the film of choice when a large area is required, showing excellent detail radiographs, for example areas of infection, uneruption or tumour. Occlusals are also taken for parallax to locate unerupted teeth and mesiodens.
What is horizontal angle?
90 degree to line of arch to avoid overlaps
What is the centring points for a PA?
Maxilla - ala trague line
mandible - 1cm above lower border of mandible
What is the centre points for oblique occlusal?
Maxilla - 1cm above ala tragus line
Mandible - through lower border of mandible
What dont we have for oblique occlusal?
external beam aiming device and connecting rod to help
Describe oblique occlusal guideline angles for the maxilla
Central beam passes through the roots of interest, one centimetre above the ala tragus line. The angle of the tube is 60 degrees to the floor for anteriors, flattening to 45 degrees for posteriors
Describe oblique occlusal guideline angles for mandible
Lower occlusal plane parallel to the floor.
Central beam passes through the roots of interest. Align the tube along the lower border of the mandible. The angle of the tube is 35/40 degrees to the head for anteriors, flattening to 20/25 degrees for posteriors
What is standard angle of tube head for upper anteriors?
60
What is the angle of tube head for upper occlusal centred on canine?
55
What is angle of tube head for upper occlusal centred on premolar ?
50
What is angle of tube head for upper occlusal on molar
45
What is angle of tube head for lower anterior occlusal?
40 to occlusal plane
What is angle for lower occlusal centred laterally?
35 to occlusal plane
What are storage phosphor plates?
Multi use sensors protected by a plastic cover and are protected from tooth marks by cardboard (single use) or plastic (multi use)
Where do storage phosphor plates go?
in between upper and lower teeth and held in place by pts bite - no damage due to covering of either cardboard or plastic
Where does black side of pshospor plate face?
x-ray source
What is the active surface of phosphor plates?
Pale blue surface
When we put the sensor into plastic over what must we ensure?
That writing can be seen through the clear side and that the side of plastic cover that is black has the phosphor side of the sensor against it and is what receives the x-ray
Where should the dot be?
Outside pts mouth
What must black surface face?
teeth we are looking at
What are true occlusal radiographs?
These are used for LOWER JAW ONLY and gives us a plain view of the teeth where beam goes through the long axis
Why can we do upper true occlusal?
We can’t get x-ray source close enough to pt as we need to go through dense bone structures so higher radiation and poorer image quality
Where does x-ray beam come for true occlusal radiographs?
Up long axis of tooth
When would we do true occlusal radiograph?
to detect submandibular duct calculi
assess buccolingual position of unerupted teeth
evaluate pathological bunco-lingual expansion
orizontal displacement of fractures
pathology - large cysts
What can a salivary gland swelling below the lower jaw indicate?
calculi in duct
What are the types of submandibular duct calculi?
concentric growth
conforms to duct
What is a concentric growth calculi?
This is where the calculi looks different - central part is more opaque as it has been mineralised longer and more layers develop around it
What is a conform to duct calculi?
This is when the calculi conforms to the duct shape
What is kissing teeth?
When premolar faces distally
