Question 1

What is a tomogram?

Accepted Answer

- Radiograph showing a slice or section of tissue in focus - Tissues either side of slice are exposed to radiation but are not clearly seen on resulting film - tissues seen are within focal trough or place - multiple tomograms of sequential planes would build up to give 3D image (e.g. CT)

Question 2

Describe tomography

Accepted Answer

- conventional tomography is rarely used nowadays - linear tomography is simplest - DPT is a form of tomography that allows us to bring the teeth and supporting structures into focus - other tissues are blurred and not clearly seen but contribute to the image we look at - this reduced the sensitivity of the technique, but our eyes and brain may not be aware of this

Question 3

describe narrow beam tomography

Accepted Answer

- synchronised movement of tube head and film/sensor - rotate round patient in horizontal plane - circular path - single centre of rotation - focal trough is an arch of circle - of limited use for dentistry as the dental arch is not part of the circle

Question 4

Describe DPT

Accepted Answer

- Dental arch elliptical shaped - focal trough is horseshoe shaped - complex rotation - usually within two centres of rotation - x-ray tube rotates behind the patient - sensory or cassette move in front of patient synchronised with tube head

Question 5

what are the disadvantages of intensifying screens?

Accepted Answer

- light is emitted in all directions - light affects larger area of film than a single photon - image quality (fine detail) is not as good as direct action film

Question 6

What is different about digital radiography?

Accepted Answer

Indirect action film and intensifying screen replaced by phosphor plates or solid-state sensor/CCD

Question 7

What are the disadvantages of DPT?

Accepted Answer

- Lack of fine detail - superimposition of other soft and hard tissues, air shadows - patient must be correctly positioned for optimal image quality - exposure time up to 16 seconds - patient co-operation required - magnification of image due to object/receptor distance

Question 8

Notes about lead apron?

Accepted Answer

- Current guidance states no justification for routine use of lead aprons in dental radiography - Does not protect from internal scatter - Interferes with image on DPT as can be projected onto image and may also catch the tube as it rotates

Question 9

Describe focal trough

Accepted Answer

We try and position the patient so that their teeth are in the middle of the focal trough - with the patient biting into the groove of the bite block. The patient brings their mandible forwards into an edge-to-edge incisal relationship - which is impossible to do if you have a class III incisal relationship

Question 10

describe DPT and caries diagnosis

Accepted Answer

- Not the "gold standard" - frequently requested when strong gag reflex - poor fine detail - overlap, particularly in premolar regions - superimposition of anatomy/air (lip shadow) - some have suggested DPT may be better for occlusal caries diagnosis (especially in molars)

Question 11

Describe caries in children

Accepted Answer

- tendency for caries to be approximal - by the time cavitation has occurred there is pulp involvement - panoramic often has overlap of contact points - better with bitewings

Question 12

What should be noted about radiographic requests?

Accepted Answer

- DPTs need to be justified - should aid diagnosis and treatment planning - referrer should know how image is acquired - patient must be able to co-operate - clinician must be able to interpret the image - principles of ALARP should always be followed

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Dental panoramic tomography 2 Flashcards

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