194 Forensic dentistrydevelopment of cancer does not have a defined dose threshold. One study
determined that the risk of fatal cancers including all organs was 0.25 per
1,000,000 full-mouth radiographic exams.^7 Risks in this and other similar
studies, however, are estimated using a linear nonthreshold model. Actual
fatal cancer risk for this amount of radiation may be more, less, or none at all;
it is scientifically unproven. For the purpose of this textbook, it is obvious that
the greatest concern to the forensic dentist involves protection to the operator
from tube head leakage and scatter radiation. However, any measures taken
to reduce t he exposure dose a nd scat ter radiation to v ictims a lso reduce expo-
sure and its ill effects to all personnel in the immediate work zone.10.7 Radiation ProtectionRadiation protection standards regarding x-ray machine safety and perfor-
mance are promulgated by the Food and Drug Administration.^8 The National
Council on Radiation Protection and Measurements (NCRP)^9 published new
guidelines and recommendations relative to use of x-radiation in dentistry in
- The document containing these guidelines supersedes NCRP Report
35, which was published in 1970. The purpose of the NCRP reports is to give
guidance to the dental profession in protecting the public and those occupa-
tionally exposed to the dangers of excessive x-radiation. The radiation safety
guidelines proposed by the American Dental Association typically follow
the NCRP reports. This section lists and describes the guidance provided
by this document.
10.7.1 Maximum Permissible Dose
Agencies typically follow the more conservative stochastic model when deter-
mining safety limits for the population, dental patients, and dental personnel.
Limits to x-radiation occupational doses are known as maximum per-
missible doses (MPDs). The MPDs are considered to be at a level that the body
can tolerate with little or no damage. The dose limits are established by com-
paring to estimated risks of occupational injury in other vocations that are
considered to be safe, such as agriculture, construction, and manufacturing.
The yearly maximum for occupationally exposed individuals is 50 mSv per
year, and the public limit is one-tenth of that, at 5 mSv per year (Table 10.2).
Note that the cumulative dose becomes more restrictive than the annual
dose over time. For example, a person who begins receiving an annual dose
of 50 mSv every year will exceed his or her cumulative maximum of 230 mSv
at age twenty-three. No ill effects or injuries have been demonstrated as a
result of anyone receiving exposures equal to established MPDs.^10