Dental panoramic tomography 2

Question 1

What is a tomogram?

Answer 1

• 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

Answer 2

• 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

Answer 3

• 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

Answer 4

• 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?

Answer 5

• 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?

Answer 6

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

Question 7

What are the disadvantages of DPT?

Answer 7

• 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?

Answer 8

• 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

Answer 9

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

Answer 10

• 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

Answer 11

• 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?

Answer 12

• 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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