1.  Definition- a specialized technique for producing radiographs showing only a section or a slice of a patient  Each tomograph shows the tissues within the focal through sharply defined and in focus

2.  Fig.14.1

3.  Maxilla and mandible are captured on one film  Tube head and film move around patient’s head in a coordinated motion.

4.  Beam of radiation-narrow slit  Film requires intensifying screens  Film placement is extraoral  Object to film distance varies  Exposure time varies from 8 to 22 seconds  Image quality is fair to moderate but significantly less details than periapical

5.  Screens have fluorescent crystals that “glow” or produce visible light when hit by an x-ray  Convert x-ray into visible light and expose the film  Reduce the patient dose significantly  Film has higher contrast than intraoral radiograph

6.  Intensifying screens have two types of crystals-calcium tungstate and rare earth  Intensifying screens have to be matched to the type of the film that responds to blue or green light

7.  Real or actual shadows- structures in or close to the focal through  Ghost or artefactual shadows- structures on the opposite side or a long way from the focal through. The 8 o upward angulation of the X- ray beam means that these ghost shadows appear at a higher level than the structures that have caused them

8. 

10.  An X-ray tubehead,  A cassette and cassette carriage assembly  Patient-positioning apparatus including light beam markers

12.  Patients should be asked to remove any earrings, jewellery, hair pins, spectacles, dentures or orthodontic appliances.  The procedure and equipment movements should be explained, to reassure patients.  A protective lead apron should be used only for pregnant patients

13.  Mid-saggital plane should be perpendicular to the floor  Frankfurth plane should be parallel to the floor  The patient should bite into notch  Tell patient to put tongue in roof of mouth and to keep still during the exposure

14.  Confirm the exposure settings  Move outside the room or behind the barrier  Watch patient during entire exposure

15.  Switch on the lateral ceph machine by pressing the C button  Unscrew the knock on the pan machine turning counterclock wise and plucking it out  Adjust the program( no 1) at the window of the pan  Press R button on the panel of the machine

16.  A large area is imaged allowing comparison on symmetrical structures  The image is easy for patients to understand and is therefore a useful teaching aid  Positioning is relatively easy  The radiation dose is one-third of the dose for the full-mouth survey

17.  Structures or abnormalities not in the focal through may not be evident  Soft tissues or air shadows can overlie the required hard tissues structures  Ghost shadows can overlie the structures in the focal through

18.  The tomographic movement together with the distance between the focal through and film produce distortion and magnification of the final image ( approx. 1.3)  The use of intensifying screens results in some loss of resolution  Not suitable for children under 5 years or on some disabled patients