DPT 1

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 plane
• multiple tomograms of sequential planes would build up to give a 3D image e.g. CT

Question 2

What are the disadvantages of intensifying screens?

Answer 2

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

Question 3

What are the basics of taking a DPT?

Answer 3

• pt must be positioned so the focal trough corresponds to the dental arch as far as possible
• x-ray tube head moves behind patient from right to left
• receptor moves in front from left to right
• only a narrow section of film is exposed at any one time or rotating sensor receives information constantly
• use bite block to bring mandible into same focal trough as maxilla
• radiation exposure and receptor movement stop if finger removed from exposure switch - cannot be restarted
• collimated view programmes available
• normal anatomy can appear distorted because of technique

Question 4

What are some advantages of a DPT?

Answer 4

• images teeth and facial bones with minimal discomfort
• shows both sides on one radiograph allowing for comparison
• shows vertical height of mandible and inferior dental canal
• shows maxillary sinus walls
• dose is reduced compared to full mouth or intra-oral radiographs, and actual time to take is less

Question 5

List some possible clinical indications of a DPT?

Answer 5

• lesion not completely visible on intra-oral
• gross dental disease/neglect
• symptomatic third molars
• orthodontic assessment
• mandibular fractures
• degenerate disease of TMJ
• implant planning or review

Question 6

What are some disadvantages of DPT?

Answer 6

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

Question 7

What are ghost images?

Answer 7

Images of a structure on one side which are projected onto other side

• angle and ramus of mandible
• hard palate
• foreign bodies (earring, surgical clip)