OPT Dental equipment; principles of operation

Question 1

what does OPT stand for

Answer 1

OrthoPanTomography

Question 2

what are the two principles that the OPT machine works off

Answer 2

1) Tomography

2) Scanography

Question 3

What is tomography- 2 points

Answer 3

• The tube and cassette/digital image receptor move together, in opposite directions, about a central pivot
• The unit moves around the patient, blurring out all structures expect the dental arches

Question 4

what is scanography- 2 points

Answer 4

• The unit uses a very narrow slit of radiation, via an aperture at the tubehead, to sequentially expose tiny sections of the image
• The image is thus built up of a series of parallel exposed strips

Question 5

What is the purpose of using 3 pivots during scanning

Answer 5

ensure that the incisors are relatively in focus as well as the molars/premolars

Question 6

What is the dose of an OPT in comparison to full mouth set of dental films

Answer 6

an OPT produces 1/3rd of the dose of full-mouth set of dental films

Question 7

how is the film exposed

Answer 7

the film is exposed from one side to the other as the machine moves around

Question 8

What is the x-ray tube like for OPTs - 3 points

Answer 8

1) the long exposure allows for a low tube current of 10-15mA
2) The rate of x-ray photon and heat production is therefore lower than a standard x-ray machine
3) this allows for the use of a fine focus (0.6mm) stationary anode tube

Question 9

what is the tube current for an OPT x-ray tube

Answer 9

10-15 mA

Question 10

what size is the fine focus that is used for an OPT

Answer 10

0.6mm

Question 11

what type of anode tube is used

Answer 11

stationary anode tube

Question 12

what is the effect of using a fine focus stationary anode tube

Answer 12

this reduces the overall bulk of the equipment and allows freedom of movement and rotation

Question 13

Name some positioning aids used to help with positing the patient- 5 points

Answer 13

1) bite block
2) chin rest
3) forehead support
4) head clamps
5) handles

Question 14

how is correct placement of the patient guided

Answer 14

by 3 positioning lights/lasers

Question 15

where should the horizontal laser line up with

Answer 15

at the level of and coincides with the Frankfurt plane- this line indicates the level of the maxillary atrium floor i.e. roof of the oral cavity

Question 16

where should the perpendicular laser line up with

Answer 16

should align with the canine tooth. Patients chin is elevated or dropped until both lasers are correctly placed

Question 17

where should the central laser line up with

Answer 17

the mid sagittal plane of the patient in order to prevent tilt of the skull

Question 18

A well position technique should (3 points)

Answer 18

1) be symmetrical
2) have no magnification or diminution of the teeth
3) have the occlusal plane flat or slight downward curve

Question 19

the Frankfurt plane should

Answer 19

be parallel to the floor

Question 20

the occlusal line should

Answer 20

be flat or have a slight downward curve

Question 21

Common positioning errors- 6 points

Answer 21

1) patient too far IN
2) patient too far OUT
3) patient in ‘chin up’ position
4) patient in ‘chin down’ position
5) Patients head is rotated
6) Patient is slumped not upright