Flashcards in Parallel Technique Deck (8):
How do you perform the parallel technique?
the plane of the image receptor is placed parallelto the long axis of the tooth.
The x ray beam is directed such that the “central ray” is perpendicular to the long axis of the tooth and the image receptor.
what are the holding and alignment devices?
stable styrofoam bite blocks
we use these only for periapical views
what are the devices for the alignment?
2. Rinn system (or similar) alignment devices
why is it difficult to get the upper one aligned? and the lower one?
a) Presence of palatal or mandibular tori.
b) Intraoral anatomy; e.g. narrow or shallow palatal vault, shallow floor of mouth.
c) Altered intraoral anatomy due to previous trauma or surgery.
d) Patient tolerance.
what are 5 advantages of the paralleling technique?
1. Dimensional accuracy*
2. Little distortion*
3. Theoretically, better definition*
4. Easy to learn and use (direction of “central ray” fairly simple to determine)
5. Reduced dose when “long cone” (16 inch FFD) used
*if and when all principles of technique can be applied - see “Rule for Accurate Shadow Casting” in lecture 5.
what does long distance between x ray source and image receptor do?
Long distance between x ray source and image receptor - x ray beam less divergent as it leaves end of position indicating device (PID or “cone”) – the x ray photons are more parallel to one another - smaller volume of tissue irradiated – SLIGHTLY less dose to patient
What is a disadvantages of the paralleling technique?
Patient discomfort with some views when you try to get the film parallel to the tooth/teeth.