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Professor Wilhelm Conrad Roentgen discovered x-rays, a form of ionizing radiation, on November 8, 1895, more than 120 years ago.  Although Roentgen conducted numerous experiments to determine the properties and characteristics of x-rays, the deleterious effects of x-radiation were not discovered initially.  Soon thereafter, it was observed that lengthy exposure to the x-ray beam resulted in burns, skin alterations and hair loss.

In 1898, Dr. William Rollins, a Harvard graduate and Boston dentist, received a severe burn on his arm while exposing his hand to the x-ray beam.  This event stimulated his interest and research in radiation protection.  In 1901, he published the results of his experiments on guinea pigs, which demonstrated the association between x-ray exposure and biological damage.1 As a result, he recommended several precautions; wear leaded glasses, enclose the x-ray tube in a leaded housing, record only the area of interest and shield the rest.1 In addition, he suggested filtration of the x-ray beam and developed rectangular collimation to restrict the size of the x-ray beam.  He published over 200 articles on x-radiation hazards in Notes on X-Light from 1897-1908.1 Although his safety suggestions were ignored, his recommendations are elements of current radiation safety and protection measures.  Rollins, like many other early pioneers, contributed to the understanding and prevention of the biologic effects of x-radiation.

Now there are a variety of international and national organizations and agencies, some with regulatory responsibilities, that analyze data, publish reports and disseminate information on radiation protection, risk estimates and units of measurement.  On the international level are the International Commission of Radiological Protection (ICRP), the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) and the International Commission on Radiation Units and Measurements (ICRU).2  On the national level are the Biological Effects of Ionizing Radiations (BEIR) Committee, the National Council on Radiation Protection and Measurements (NCRP), the Nuclear Regulatory Commission (NRC), the Environmental Protection Agency (EPA), the Occupational Safety and Health Administration (OSHA) and the National Center for Devices and Radiological Health (NCDRH), the U. S. Food and Drug Administration (FDA) and the U. S. Department of Health and Human Services (HHS).2  A rather sophisticated network of organizations, agencies and bureaus deal with varying aspects of radiation and radiation protection.  In addition, there are federal and state laws that regulate dental x-ray equipment, x-ray machine inspection and the credentialing of dental radiographers.

This brief summary demonstrates how the study of radiation biology began and how radiation safety and protection measures evolved from early research efforts to formally established organizations that examine leading scientific thought and provide guidance and recommendations on radiation protection and measurement. The subsequent information will provide an overview of radiation biology and the safety and protection measures that the dental assistant can implement to reduce radiation exposure to dental patients as well as minimize occupational exposure.  This information applies to both film-based and digital radiography.


Gail F. Williamson, RDH, MS, is a Professor of Dental Diagnostic Sciences in the Department of Oral Pathology, Medicine and Radiology at Indiana University School of Dentistry in Indianapolis, Indiana. She received an A. S. in Dental Hygiene, a B. S. in Allied Health and a M. S. in Education from Indiana University. She serves as Director of Allied Dental Radiology and Course Director for Dental Assisting and Dental Hygiene Radiology Courses. A veteran teacher, Prof. Williamson has received numerous awards for teaching excellence. She is a published author and presents numerous continuing education courses on Oral and Maxillofacial Radiology on the national, regional, state and local levels.


Upon completion of this course, the dental professional should be able to:
• Discuss the direct and indirect effects of radiation.
• Summarize the short and long-term effects of radiation, the latent period and cumulative effect.
• Describe the Law of Bergonié and Tribondeau and discuss its application to radiation biology.
• Define radiosensitivity and discuss the relative sensitivity of different types of cells, tissues or organs.
• Explain the impact that LET, dose, volume of exposed tissue and stochastic and non-stochastic effects have on radiation damage of human tissues.
• Differentiate between somatic and genetic tissues.
• Define and describe the units of radiation measurement: exposure, air kerma, absorbed dose, equivalent dose, effective dose and radioactivity.
• Discuss the ALARA principle and its relevance to radiation protection.
• Outline the principles of selection criteria and discuss how they impact patient exposure.
• Identify and describe the methods of reducing radiation exposure to dental patients.
• Differentiate primary, secondary and leakage radiation.
• Discuss the radiation safety and protection measures that minimize occupational exposure.
• Identify primary and secondary barriers and how barrier specifications are determined.
• Define the dose limit (DL) for occupationally exposed persons and describe methods to monitor safety habits and compliance with the DL.


The ADAA has an obligation to disseminate knowledge in the field of dentistry. Sponsorship of a continuing education program by the ADAA does not necessarily imply endorsement of a particular philosophy, product or technique.

The ADAA cautions participants taking this course on the hazards of using limited knowledge when integrating new techniques into their practices.

Credits earned upon completion of the course may be used to meet DANB’s Recertification Requirements.


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