R: Formation of the radiographic image Flashcards
Label
What are the two visual characteristics of an x-ray?
Dense tissue will appear radioopaque or radioluscent?
What influences the sharpness and resolution (geometric characteristics) of a dental radiograph ?
Factors
affecting a
radiographic
image
Angulation
Orientation
Magnification
Soft Tissue Shadow
How should the beam and film be angled? What 2 introral xray techniques are there?
(Concept: Anglelation)
Refers to the angulation of the
central beam
Film parallel to the long axis of the
tooth
Central beam perpendicular the
film and tooth
2 intra-oral techniques- bisecting
angle and paralleling
Horizontal Angulation example
Explain the concept of bisecting angle:
Basically.
- You have long axis of tooth.
- You have film placed parallel to tooth.
- Imagine an IMAGINARY LINE BETWEEN THE TOOTH AND FILM.
You want to angle the beam so it hits this imaginary ‘bisecting line’
Paralleling technique
The beams ORIENTATION can affect_______
The orientation of a particular
feature(anatomy/film position) to the central
beam can affect its radiographic appearance
How do you avoid magnification
Increase in the size of the image on the radiograph
compared with the actual size of the tooth
Overall increase; no shape distortion
How to avoid?
1. Keep the tooth close to the film. I.e. decrease tooth to film distance
keep beam at distance to the film. I.e. increase target to film distance
What can over impose on X-rays and I fluency what we see?
Soft Tissue Shadows
Explain shape distortion and give an example of how it can occur and how would you fix it…
Distortion= unequal magnification of different parts of
the same object
1. Happens bc not all parts of the tooth are at same distance from the focal spot
E.g. this may be because of the shape of tooth- common with maxillary molars
2. Results in differences in appearance of the
image on a radiograph compared to the true shape
TO FIX IT…
1. Can be minimized by placing the sensor parallel to the LONG axis of the tooth and by orienting the central RAY at right angles to
the tooth and sensor
Happens because maxillary molars have 3 roots (unlike mandibular). In image- it looks like there is 2 short buccal roots and a long palatal root at the back. In reality the roots are actually SIMILAR LENGTH but because the roots are on different planes this creates ‘shape distortion’.
Characteristics of
an ideal image
1.Focal spot/target- as small as possible
set by the machine
2. Target to tooth distance-as long as
possible,use long cone/paralleling
technique
3. Tooth to film distance-as less as
possible,placing the film as close to the
tooth as possible without bending the
film
4. Film parallel to the tooth
5. X ray beam perpendicular to the tooth
and film
Film coverage-make sure the film covers the tooth of interest entirely; plus 2-3 mm of normal surrounding bone.
Which x-ray is ideal? Explain.
Can these x-rays be used for diagnosis? Explain
Does this image have correct horizontal angulation?
Yes
Is this Bitewing x-ray ideal?
No you can see white overlaps (incorrect horizontal angulation), correct image is first one:
Identify soft tissue features of the following x-rays:
