Paralleling Technique

Question 1

What is the theory of the paralleling technique?

Answer 1

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

Question 2

Why does PT produce the most accurate image of the teeth?

Answer 2

The tooth and the receptor are parallel

Question 3

What conditions are necessary to produce the most accurate image of the teeth?

Answer 3

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

Question 4

Short Cone vs Long Cone

Which is better? Why?

Answer 4

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

Question 5

What is the PID?

Answer 5

Position indicating device

AKA Cone

Question 6

What is horizontal angulation?

Answer 6

Sideways placement of cone tip (back and forth)

Question 7

Rule of horizontal angulation

Answer 7

Central ray must pass through the teeth parallel to the proximal surfaces (surface that touches adjacent tooth)

Question 8

Errors in horizontal angulation

Answer 8

If the CR is not parallel to the teeth, overlapping of the proximal spaces will occur

Will not be able to see cavities

Question 9

Horizontal angulation in the operatory

Answer 9

Receptor is horizontally parallel to the angle of the arch of the teeth to be exposed

Question 10

Vertical Angulation

Answer 10

Up and down angulation of the cone

Question 11

Rule of vertical angulation

Answer 11

All angulations above the occlusal line are +

All angulations below the occlusal line are -

Question 12

Errors in vertical angulation

Answer 12

Elongation if vertical angulation is too low (not enough)

Foreshortening if vertical angulation is too high (too much)

Question 13

Vertical angulation in the operatory

Answer 13

Receptor is vertically parallel to the long axis of the tooth

Question 14

What are two indications for switching to BAT from the parallel technique?

Answer 14

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

Question 15

How do you achieve proper vertical angulation?

Answer 15

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

Question 16

How should the receptor be placed for anterior PA’s and bite-wings?

Answer 16

Vertical receptor placement

Question 17

How should the receptor be placed for posterior PA’s and bite-wings?

Answer 17

Horizontal receptor placement

Question 18

What are the two colors of XCP rings? What are they each used for?

Answer 18

Blue= anterior PA's
Yellow= posterior PA's

Question 19

What are the three parts of an XCP instrument?

Answer 19

Indicator rod- parallel to long cone
Locator ring- direct xray beam through
Bite block- patients occlude on block

Question 20

Benefits of an intra oral receptor holder

Answer 20

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)

Question 21

The further away the the radiation has to travel to the receptor, the more it is diminished and adjustments may be necessary

Answer 21

Increase in kilovoltage, milliamperage, exposure time (most frequent change), speed of film

Question 22

How many images are taken in an adult and pedo FMS?

Answer 22

Adult= 20
Pedo w/ primary/deciduous= 8
pedo w/ parmanent=8-20 depending on age and size

Question 23

What order do you take the FMS in? Why?

Answer 23

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

Question 24

What is the angulation the PID should be at for bite-wing exposures?

Answer 24

+5 or 10 degrees

Question 25

How to prevent cone cut in a bite-wing

Answer 25

Middle of the cone is at the occlusal plane

Cone is 1/4” anterior to the receptor

Question 26

What do you do if a patient who is partially edentulous needs a bite-wing?

Answer 26

Allow them to wear denture in the opposite arch to stabilize tab
If no denture, place a cotton roll