Forensic Dentistry, Second Edition

Forensic dental radiography 193

effect occurs when the x-ray energy ionizes water into ion pairs or free radi-

cals, which then produce damage to molecules within the host. Most damage

from x-radiation does occur through the ionization or radiolysis of water.

There are numerous biological molecules that can be adversely affected by

x-ray energy, including nucleic acids and proteins. Damage at the cellular

level affects the nucleus, cytoplasm, and chromosomes and may result in

cell and eventually host death. Given enough ionizing radiation, damage

will occur with whole body systems such as the gastrointestinal organs and

hematopoetic system.

Predicting damage from x-radiation falls follows two distinct models:

deterministic and stochastic. Deterministic effects occur with large doses

that produce certain types of bodily damage for which a definite threshold

may be determined and damage increases above that threshold. Stochastic

effects typically do not have a known threshold, are all or none in effect, and

typically relate to cancer and genetic effects. In lieu of a threshold with sto-

chastic damage, it is a matter of continuing higher odds of damage as the dose

is increased. Dental radiographic exposures are typically low to the point of

not reaching threshold doses required to cause deterministic somatic damage

such as skin burns, damage to the lens of the eye, or hair loss. However, the

Table 10.1 Factors Affecting the Image Quality

Factor Density Contrast Scale (Shades of Gray)

mA Increases

Exposure time Increases

kVp Increases Increases (more shades of gray)

Aluminum Decreases Increases (more shades of gray)

Distance Decreases

Exposure time and mA control density; kVp alters film contrast.

Figure 10.2 setup for exposing a postmortem radiograph. proper projection
geometry is critical whether using film or digital sensors.