Summary Radiographic examinations play an essential part of dental practice. Because a certain amount of radiation is inevitably delivered to patients, it should be as low as reasonably achievable. The purposes of this article are to review the definition of the dose, the concept of the radiation protection, the measurement of the dose in dental radiography, and means to reduce dose through effective selection of patients and the management of radiographic equipment. The effective dose from some dental radiographic examinations is high enough to warrant reconsideration of means to reduce patient exposure. By using digital sensors or F-speed film, instead of D-speed film, combined with rectangular collimation instead of round collimation, dentists can reduce patient's exposure by a factor of 10 for bitewing and full-mouth radiographs. Justification and optimization of a procedure along with dose limitations are essential in clinical practice. It is prudent to establish diagnostic reference levels for dental radiography in Japan. In addition, dentists should remain informed about safety updates and availability of new equipment, supplies and techniques that would further improve the diagnostic ability of radiographs and simultaneously decrease patient exposure. Keywords Dental radiologyEffective dosePatient selection criteriaQuality assuranceRadiation protectionDiagnostic reference levels 1. Introduction Radiation is indispensable in modern medicine. The radiographic examination is one of the principal diagnostic methods used in all fields of medical services and contributes to the promotion of the health, both individually and nationally. Accordingly, a certain amount of radiation is inevitably delivered to patients and populations. In Japan the average dose to the population from diagnostic radiology may be equivalent or even more than from the natural background exposure . The adverse effects to humans, such as radiation carcinogenesis, can be considered on the basis of a hypothesis so-called a linear no-threshold (LNT) model, which was scientifically presumed from the epidemiological studies including atomic bomb survivors of Hiroshima and Nagasaki . On this assumption, the risk associated with low-level diagnostic exposures could be expected to be low but greater than zero. For this reason it is prerequisite to measure the dose to the patients in the diagnostic radiology precisely. In addition, the radiation dose to the patients should be as low as reasonably achievable, a principle known as ALARA . The number of diagnostic examinations should also be taken into consideration because the risk is directly proportional to the frequency of X-ray exposure. Dental radiographic examinations are one of the most frequently performed radiological studies in Japan. A survey in 1999 estimated that dentists were making 82 million intraoral radiographs and more than 12 million panoramic radiographs each year . The effective dose delivered to patients per radiograph is low but the collective dose is significant because of the large number of radiographs made. A unique aspect of radiological protection in medicine, which differs somewhat from other types of radiation exposure, is that the details of a medical radiographic examination are up to the discretion of the clinician. Such decisions are made on the basis of the anticipated health benefit to the patient. The decision is always made based on the professional judgment of the doctor in charge of the patient, with informed consent, which includes not only the expected benefit but also the potential risk . In the case of low risk procedures such as dental and chest radiography, the degree of informed consent may be low, even where the cultural or societal factors have to be considered. The benefit of a particular examination in medical practice is qualified by consideration of evidence-based medical literature . The effective usage of radiation in dental practice has been studied for many years and several guidelines have been proposed . Dentists and other dental health care personnel should use these well-thought-out and research-proven guidelines, which benefits patients by reducing not only the radiation dose but also the cost . Another aspect of protection in medicine is to consider optimization of radiographic procedures. Reduction in exposure dose to patients may be attained by proper management of equipment and the accomplishment of a quality assurance program . The goal of optimization is to keep the dose “ALARA, economic and societal factors being taken into account,” and is best described in medical practice as: management of the radiation dose to the patient to be commensurate with the medical purpose . The purposes of this article are to review definitions of dose, the concept of radiation protection, the measurement of dose in dental radiography, and ways to reduce dose through effective use of X-ray and the management of equipment. 2. Radiation dose and effects 2.1. Definitions of dose used in radiation protection The absorbed dose, D, is the basic physical dose quantity, and it is used for all types of ionizing radiation. It is defined as the mean energy imparted to matter of mass by ionizing radiation . The SI unit of absorbed dose is J/kg and its special name is gray (Gy). The protection quantity equivalent dose in an organ or tissue, HT, is defined by HT=∑RwRDT,Rwhere DT,R is the average absorbed dose in the volume of a specified organ or tissue T, and wR is the radiation weighting factor for radiation R. The values of wR are defined largely on the basis of the relative biological effectiveness of the different radiations. The sum is performed over all types of radiations involved if an individual is exposed to more than one type of radiation. The unit of equivalent dose is J/kg and has the special name sievert (Sv). As wR of X-ray is 1, so 1 Gy in dental radiology corresponds to 1 Sv. ! Uwagi: Brzegi stron zakurzone i zabrudzone. Oprawa zarysowana i zabrudzona. Książka posiada pieczątkę.