Parallel Technique

Question 1

How do you perform the parallel technique?

Answer 1

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.

Question 2

what are the holding and alignment devices?

Answer 2

stable styrofoam bite blocks

we use these only for periapical views

Question 3

what are the devices for the alignment?

Answer 3

2. Rinn system (or similar) alignment devices

Question 4

why is it difficult to get the upper one aligned? and the lower one?

Answer 4

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.

Question 5

what are 5 advantages of the paralleling technique?

Answer 5

1. Dimensional accuracy*
   2. Little distortion*
   3. Theoretically, better definition*
   4. Easy to learn and use (direction of “central ray” fairly simple to determine)
2. 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.

Question 6

what does long distance between x ray source and image receptor do?

Answer 6

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

Question 7

What is a disadvantages of the paralleling technique?

Answer 7

Patient discomfort with some views when you try to get the film parallel to the tooth/teeth.

Question 8

what are some limitations in using the paralleling technique?

Answer 8

1. ANATOMIC: - tori - shallow floor of mouth - shallow palatal vault - muscle and frenal attachments
2. PATIENT TOLERANCE