b. The generally accepted theory as to the nature of changes occurring in the
production of the latent image is that, when the silver bromide crystals are atomically
activated by exposure to x-rays (and usually, the fluorescent light of intensifying
screens), electrons fly out of their normal atomic orbits and wander at random
throughout the crystals. These are known as photoelectrons (B, figure 1-6), one of
which (in dotted box, B, figure 1-6) is theoretically represented in C through I, figure 1-6.
Normally, the silver bromide crystal is a nonconductor of electricity. Upon exposure to
x-rays or light, however, it becomes a weak conductor and the photoelectrons, released
from the individual atoms in the crystal flow within the crystal as a tiny electric current
(C, figure. 1-6). Ultimately, some of these electrons are trapped or acquired by the
"speck" (D, figure 1-6). A negative electrostatic field is now set up around the "speck."
Other activities also occur in the crystal for the slower-moving silver ions with a positive
charge travel (E, figure 1-6) to the negatively charged "specks" where they are
neutralized (F, figure 1-6) to form tiny particles of atomic silver, while the bromide
portions of the crystal are absorbed elsewhere. As more silver ions are neutralized, the
"speck" grows with silver (G, figure. 1-6). In I, figure 1-6, the silver has been reduced to
metallic silver by the action of the developer.
c. The latent image cannot be seen or detected by ordinary physical means, but
it can be changed into a visible silver image by chemical processing.
DENTAL X-RAY FILM
Even though most radiographers do not perform dental radiographs,
Radiographers should be aware of the different sizes and types of dental film. Dental
x-ray films are available in different sizes and types.
a. Periapical Film. The periapical film is used to radiograph the crown root and
supporting structure of the teeth. It is particularly useful to determine abscesses, cysts,
or granulomas located at the root apices. Additionally, periapical film has great value in
diagnosing bone loss caused by periodontal disease. Full mouth periapical series are
also used as a record of the progression of such diseases.
b. Bitewing Film. The interproximal or bitewing film is used principally to locate
cavities on the interproximal surfaces of the teeth (surfaces facing other teeth). These
include the crown portion of the tooth and a small area of the root. To hold the film in
position, the patient's teeth close on the tab,, which is attached to the film packet.
c. Occlusal Film. The occlusal film is a larger film, which is placed horizontally
between the occlusal (chewing) surfaces of the upper and lower teeth. The occlusal
film provides a general view of the maxillary (upper jaw) and mandibular (lower jaw)
arches, so it is especially useful in locating foreign bodies in the floor of the oral cavity
and impacted teeth, cysts, et cetera, in the palate. There are usually two films in the
occlusal packet, which allow for different developing times. In medical radiography,
occlusal film is also used for examination of the nasal bones and to demonstrate stones
in the salivary tracts.