Radiographic Localisation Flashcards
what is the need for radiographic localisation
- to determine location of a structure or pathological lesion in relation to other structures
- only needed where clinical examination insufficient to provide answer
• clinical examination must always occur prior to radiographic examination
○ Only way to work out the best views for that particular clinical question
what clinical situations require radiographic localisation
- position of unerupted teeth
- location of roots/root canals
- relationship of pathological lesions
• trauma
○ Dental
§ Such as fractured incisors
○ bone fractures
• soft tissue swellings - ? tissue/source
what are the clinical situations where the position of unerupted teeth need radiographic localisation
○ normal but impacted/ectopic
§ Impacted = prevented from reaching their normal occlusal plane position
§ Ectopic = unusual place
○ Supernumerary
§ If these look like normal teeth we call them supplemental teeth
§ Others look different, usually smaller
§ See these often in the upper anterior region of the maxilla
○ proximity to important structures
§ Eg in the mandible in relation to the inferior alveolar canal
§ Eg in the maxillary in relation to the maxillary sinus
when would you need to see the location of roots and root canals
○ endodontics
§ Sometimes there is difficulty in seeing all of the canals
○ Surgery
§ If you were going to do surgery to remove retained roots then it would also be important
why do we need radiographic localisation for soft tissue swellings
○ We generally consider radiographs as important for hard tissue structures we can also think of radiographic localisation as being useful when we have a soft tissue swelling and we are trying to work out what tissue is it and what is the source of that swelling
§ The source of a swelling, particularly if its an infection, might be a tooth
how are radiographs used sequentially
• Observation - look and see
○ Ie the looking has to have a result
• Interpretation - listen and think
○ We then put what we see and what we have heard from the patient and what we discovered from the clinical exam together to come up with an interpretation
• Management - patient’s needs
○ Important to remember what the patient said they were concerned about because that might not be what you have discovered
○ Or what you think is important to them there might be something else that is more important
how do you spot and correct faults or diagnostic puzzles
• Perception
○ Looking and seeing
- recognition
- resolution
Influenced by knowledge base
when looking at a radiograph in observation what needs to be considered
○ ? technical acceptability
○ ? abnormalities
○ ? need for further radiography
when describing impacted 3rd molars what needs to be said
When we describe impacted 3rd molars we say what their angulation is
§ When we are talking about angulation we are looking at the long axis of the tooth and we are describing it relative to the tooth in front which is of course is normally a 7
§ So if we look at the long axis of the 7, horizontally impacted 3rd molars would have its long axis like the bit on the end of the radiograph (extreme right) which is clearly not correct
§ If it is a vertically impacted tooth then it would have it’s long axis parallel to that but this is also not the case in this radiograph
§ If we were to draw a line down the long axis of the 3rd molar it would make an angle with the long axis of the 7 which means it is not parallel but is actually slightly disto-angular
what are the options for taking views at right angles
• panoramic and lower true occlusal
○ Panoramic is often the starting point on a lower true occlusal
• paralleling periapical and lower true occlusal
• CBCT (cone beam CT) – each of the MPRs is at right angles to the others
○ So if plain films are not going to give us the answer we will sometimes use CBCT
what are the methods of radiographic localisation
• normally two views required
○ Obviously have to be different
- views at right angles in their projection geometry
- views with any different projection, provided the difference is known
• with the aid of opaque objects (e.g. gutta percha point)
○ Eg if a patient is presenting with a sinus track in their mouth which you know is coming from a non-vital tooth but you are not sure what tooth it is you could put a GP point into that sinus opening and then take a radiograph and it should show you want apex of what tooth is the problem
• anatomical knowledge crucial
what views are not at right angles
• known projection geometry
○ Need to know how they are taken
• must both include item to be localised and a stable reference point
○ Ideally the reference should have a bit of it which is inside the mouth so we really know where it is
• multiple combinations possible
○ But they all use horizontal or vertical tube shift
• utilise horizontal or vertical “tube shift” to aid interpretation
○ This is moving the x-ray tube either horizontally or vertically and it is using what we call parallax
what is parallax
= an apparent change in the position of an object, caused by a real change in the position of the observer
how does parallax work
Imagine looking into a cupboard and moving your head:
the objects appear to change their relationship – to each other and to you
- First picture
○ can see some objects
○ Can make something out behind the jaw but we don’t know what it is - If we move our head to the right (second picture) it changes your point of view
○ Notice that the structures behind the front thing have also moved to the right
○ The object that is furthest back has moved furthest to the right
○ So there is a gradation in how far things will move
○ The objects themselves haven’t actually changed so that is the equivalent to a horizontal tube shift - If you were then to stand up, which gives you another view point then this would be the equivalent to a vertical tube shift (as well as a horizontal tube shift)
○ 3rd picture
○ Now you will see that as you get further away from the front the objects also go higher up
○ The furthest back one moves higher up than the ones in front of it
○ We see exactly the same gradation when we look at radiographs
look up pictures in lecture but not overly important because just of a food cupboard but helps w explanation
explain viewing and beam direction
- Radiographs normally viewed from the buccal aspect of the patient, therefore:
- beam “passing” from buccal to lingual
• buccal is closest to observer
○ This means that the buccal object is the closest to the observer
○ Ie it is the nearest finger
§ (ie you put 1 finger up on each hand and place 1 in front of the other)
• lingual/palatal is furthest from observer
○ Ie it is the furthest finger
• mnemonics can help to determine result of movement seen in the radiograph, when comparing the position of one structure to another
