2.4 - Occlusal Radiographs Flashcards by Amy Rooney

Where does image receptor go for occlusal radiographs?

in occlusal plane

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What size image receptor do we use for adults?

Larger 7x5cm

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What image receptor do we use for children?

size 2 PA 2x4cm

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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

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What do oblique occlusal allow us to see?

Extent of pathology

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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

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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

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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)

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In occlusal radiographs using bisecting angle technique what must the x-ray beam be?

bisecting the angle between the teeth and the receptor.

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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

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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

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What happens if the beam is at 90 degrees to image receptor in occlusal radiographs?

foreshortened image

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What happens if beam is at 90 degrees to bisector?

good image using correct bisecting angle technique

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What is the bisecting angle formed by?

Long axis of tooth and plane of image

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How much of the image receptor should be visible beyond incisal edge?

2-3mm

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If incisors are proclined what will we need to do?

increase angle

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If incisors are retroclined what do we need to do?

decrease angle

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What is the head position when taking oblique occlusal?

Occlusal plane of jaw being examined to be horizontal

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When is occlusal plane altered?

When mouth is opened

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When taking oblique occlusal of maxilla what reference plane do we use?

the ala trague line must be horizontal

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What is ala tragus line?

ala of nose to tragus of the ear

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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?

What is the angle of tube head for upper occlusal centred on canine?

What is angle of tube head for upper occlusal centred on premolar ?

What is angle of tube head for upper occlusal on molar

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