Paralleling Technique Flashcards
What is the theory of the paralleling technique?
The long axis of the tooth and receptor are parallel to each other
The central ray is directed perpendicular to the long axis of the tooth and the receptor
Why does PT produce the most accurate image of the teeth?
The tooth and the receptor are parallel
What conditions are necessary to produce the most accurate image of the teeth?
Tooth parallel to receptor
Tooth as close to the receptor as possible
Source of the xray must be small
Source of xray must be as far from the tooth as possible
Radiation must strike the object and receptor at a right angle
Short Cone vs Long Cone
Which is better? Why?
Long Cone is 16”
Short Cone is 8”
Long cone preferred so that the xray source is as far from tooth as possible.
Shorter cone will magnify the tooth and image will not be as accurate
What is the PID?
Position indicating device
AKA Cone
What is horizontal angulation?
Sideways placement of cone tip (back and forth)
Rule of horizontal angulation
Central ray must pass through the teeth parallel to the proximal surfaces (surface that touches adjacent tooth)
Errors in horizontal angulation
If the CR is not parallel to the teeth, overlapping of the proximal spaces will occur
Will not be able to see cavities
Horizontal angulation in the operatory
Receptor is horizontally parallel to the angle of the arch of the teeth to be exposed
Vertical Angulation
Up and down angulation of the cone
Rule of vertical angulation
All angulations above the occlusal line are +
All angulations below the occlusal line are -
Errors in vertical angulation
Elongation if vertical angulation is too low (not enough)
Foreshortening if vertical angulation is too high (too much)
Vertical angulation in the operatory
Receptor is vertically parallel to the long axis of the tooth
What are two indications for switching to BAT from the parallel technique?
If tooth and receptor have more than a 20 degree loss of parallelism, elongation will occur
If the patient cannot close on a bite block
How do you achieve proper vertical angulation?
Receptor must be placed vertically parallel to the long axis of the tooth
XCP must be properly set up (indicator rod parallel with cone, and at same angle as line marked on the cone
Locator ring and tube head must be parallel to each other
How should the receptor be placed for anterior PA’s and bite-wings?
Vertical receptor placement
How should the receptor be placed for posterior PA’s and bite-wings?
Horizontal receptor placement
What are the two colors of XCP rings? What are they each used for?
Blue= anterior PA's Yellow= posterior PA's
What are the three parts of an XCP instrument?
Indicator rod- parallel to long cone
Locator ring- direct xray beam through
Bite block- patients occlude on block
Benefits of an intra oral receptor holder
Enable teeth and receptor to be parallel
Enables receptor to remain rigid and flat against the holder (in patients w/ low palate, receptor will bend, switch to BAT if too much bend)
Holds receptor far enough from teeth so that it can still be parallel to teeth but avoid restrictions cause by the oral anatomy (ex. tori)
The further away the the radiation has to travel to the receptor, the more it is diminished and adjustments may be necessary
Increase in kilovoltage, milliamperage, exposure time (most frequent change), speed of film
How many images are taken in an adult and pedo FMS?
Adult= 20
Pedo w/ primary/deciduous= 8
pedo w/ parmanent=8-20 depending on age and size
What order do you take the FMS in? Why?
Anteriors first, followed by molars, finish with bite-wings.
Anterior and bite-wings are easiest for the patient, especially one with a strong gag reflex
What is the angulation the PID should be at for bite-wing exposures?
+5 or 10 degrees
How to prevent cone cut in a bite-wing
Middle of the cone is at the occlusal plane
Cone is 1/4” anterior to the receptor
What do you do if a patient who is partially edentulous needs a bite-wing?
Allow them to wear denture in the opposite arch to stabilize tab
If no denture, place a cotton roll
