192 Forensic dentistry
passive water wash tank should not be used in mass fatality incidences where
the film volume will rapidly weaken fixer solutions and contaminate the
wash tank. Likewise, “endo” processor settings should never be used due to
underprocessing and an eventual loss of archival film quality.
Darkroom safelights must also be used properly, including matching
the appropriate safelight filter with the type of films and extraoral screen
being used. The Kodak GBX-II is safe for all dental films currently available.
However, it is important to note that films are not totally insensitive to the
light emanating from appropriate safelights. Regardless of the filter used, the
safelight must be positioned at least 4 feet away from the work surface area,
and bulbs within the safelight should be no stronger than 15 watts. Working
time under safelights should also be restricted to as short a time as possible.
10.5 Intraoral Radiographic Techniques
Many x-ray generators have variable kilovoltage (kVp), milliampere (mA),
and exposure time settings. Variation in milliampere and exposure time will
affect only the density (overall blackness of the resulting image) and have
no effect on visual contrast (shades of gray). They affect the image density
equally so that doubling the milliampere setting on the unit will allow the
x-ray exposure time to be cut in half and vice versa. Variation in the kilovolt-
age setting will, however, affect both density and contrast. As the kilovoltage
is increased there will be an increase in density. However, there can also be
an undesirable increase in shades of gray in the images with a loss of distinct
blacks and whites, resulting in low visual contrast in the image (Table 10.1).
The projection geometry when exposing images of a specimen is simple
and straightforward. The receptor should be placed parallel to the denti-
tion and the beam should be directed perpendicular to the receptor plane
(Figure 10.2). Ideal imaging in many cases may be improved by resecting the
mandible and maxilla.
10.6 Biological Effects of X-rays
All human tissues are adversely affected by ionizing radiation, particu-
larly cells with high mitotic rates such as those in developing embryos,
blood-producing tissue, and reproductive organs. Were it not for this selec-
tive sensitivity, x-radiation as a treatment to kill rapidly growing, immature
tissues of neoplasms while creating less damage in normal healthy tissues
would be ineffective. Tissue and host damage occurs through two mecha-
nisms: direct and indirect. When the damaging energy is delivered directly
from the x-ray photon to the molecule, it is deemed a direct effect. An indirect