Forensic Dentistry, Second Edition

Forensic dental radiography 195

Protection of x-ray operators and surrounding personnel is provided by

the patient protection practices detailed above and by workplace wall shield-

ing and the maintenance of proper operator distance. Operators must be able

to stand at least 2 m away from the source of x-ray scatter (i.e., the patient’s

head) and out of the primary beam (Figure 10.3). If this is done, no barrier

is required. If the operator cannot stand at this desired distance, a protective

barrier or apron must then be provided. Most published research shows that

x-ray doses in dentistry continue to decline. This is most likely due to the

dramatic reduction in exposure times brought about by high-speed film and

even more so by direct digital receptors.

10.7.2 Personnel Monitoring

The decision of whether dental personnel are monitored for x-ray exposure

depends on state law and the expected exposure predicted on the basis of

workload and protective measures. The NCRP recommends monitoring to all

personnel who are likely to receive an effective dose greater than 1 mSv/year.

Many states require monitoring only if the exposure will exceed one-tenth

of the applicable MPD (5 mSv). Past studies of occupational exposure to a

large sample of dental personnel have shown that the typical exposure is less

than the minimum detectable dose, or less than 1 mSv/year.12,13 These data

Table 10.2 Maximum Permissible Doses for Dental Operators
Occupational 50 mSv annual effective dose
10 mSv × age (y) maximum cumulative effective dose
Public 5 mSv annual effective dose for infrequent exposure
Embryo and fetus 0.5 mSv equivalent dose in a month from occupational exposure
of the mother once pregnancy is known
Annual U.S. background 3.65 mSv per year

Public MPDs are one-tenth that of those who are occupationally exposed.

Posterior

Anterior

Primary

Beam

Exit

RightLift

X

X Primary Beam

Entrance

Figure 10.3 Graphic showing typical scatter pattern involved when exposing
a specimen. the safer areas are behind, indicated by X. (plotted from data from
de haan and van aken.^11 )