Intra-Oral Techniques Flashcards
What is the ideal projection geometry? (3 points)
- image receptor and object in contact and parallel
- parallel beam of x-rays
- X-ray beam perpendicular to object (patient) plane and image receptor
If ideal projection geometry was possible with intra-oral radiographs, what would the image outcome be like?
Image size would be identical to object size

What are some problems with getting an ideal projection geometry when taking an intra-oral image of a tooth?
- image receptor and object not in contact (tooth in bone so can only contact part of it)
- X-ray beam central ray MAY or MAY NOT be perpendicular to object plane and image receptor
Why is the image size not identical to the object size?
Due to magnification because of divergent beams
What are the 2 solutions to the probs with projection geometry (two techniques)?
- Paralleling technique
- Bisecting angle technique
What is the paralleling technique?
- The image receptor and the object are parallel but not in contact
- The x-ray beam is directed at right angles to the image receptor
In the paralleling technique, describe the x-ray beams with regards to being perpendicular to the image receptor/long axis of the tooth.
Only the central beam is truly perpendicular to the long axis of the tooth and image receptor
The outer beams aren’t quite perpendicular due to divergent beams
Why do divergent beams happen in paralleling technique?
because of the distance between the image receptor and object being x-rayed (allows potential for undesired magnification)
What can be used to help reduce the magnification?
A short focus to skin distance

What are the benefits of film holders and beam-aiming devices?
- dose reduction
- improved quality
- fewer rejects/retakes
Describe the parts/components of the film holder devices.
have a bite, block, beam aiming device, image receptor support
How are film holders sterilised?
They are autoclvaed
Incorrect assembly of film holders can result in what?
‘coning off’ - only part of the receptor reached so full image not made

What is the extra part found on an endodontic film holder?
A basket to support instrument heads or gutta percha points
What is rectangular collimation and why is it used?
It controls shape and size of the x-ray beam and therefore allows dose reduction Rectangular to match the image receptor
How do collimators work?
Dark area around edge is lead and very good at absorbing x-rays The x-rays cannot get out from anywhere apart from the silvery section in the middle

What is the summary of the paralleling technique?
- Image receptor and object parallel but not in contact
- image receptor and object a distance apart
- use long xray focus
- skin fsd to reduce magnification
- requires use of film holders
- stabilise with cotton roll between bite block and teeth in arch OPPOSITE to that being xrayed
How are periapicals/bitewings taken? write down and refer to notes
FOR THE TECHNIQUES ON HOW TO TAKE X-RAYS REFER TO NOTES
What is the curve of Spee?
‘happy smile’ Curves up posteriorly (seen from antero-posterior view)
What is the curve of Monson/why is it relevant?
A bucco-lingual angulation Influences x-ray technique e.g. bitewings are panoramic