DCA05DR Dental Radiation Health, Safety, and Protection, 3rd Edition _______________________________
MECHANISMS OF RADIATION INJURY The human body at its most basic level is composed of atoms. Ionizing radiation can produce injury through interactions at the atomic level when x-ray photons remove or excite orbital electrons and deposit energy within the tissue. When an x-ray photon dislodges an orbital electron, the normal equilibrium, or ground state, of the atom is disrupted and ion pairs are formed. The ionized atom becomes positively charged (+ ion) and the ejected electron carries a negative charge (– ion). To regain equilibrium, ions either recombine or combine with other atoms or molecules to return to neutral status. With excitation, a low-energy x-ray photon interacts with an outer-shell orbital electron. The energy of the photon is transferred to the electron, causing it to become excited but not ejected. When the x-ray photon ceases to exist, the excited electron releases a secondary photon of equivalent energy, and the atom returns to the ground state. The secondary photon is ejected and may produce ionization at another site. When an atom is ionized, its chemical binding properties are modified. If the ionized atom is part of a large molecule, ionization may result in breakage of the molecule or a change in location of the atom within the molecular structure (Tarrence, 2020). The altered molecule may not function normally, or it may stop functioning altogether, causing severe impairment or cell death. Radiation injury can be reversed by gaining free electrons at the atomic level or through enzymatic repair at the molecular level. The body has a tremendous capacity to repair and regenerate affected cells and tissues to aid recovery. However, the effects of radiation are additive, and some damage remains unrepaired. The cumulative effect of radiation is residual, unrepaired injury that accrues with repeated radiation exposure. Figure 1 provides an overview of possible events following radiation exposure.
The benefits of using ionizing radiation in medicine and dentistry for the diagnosis and treatment of disease and injury cannot be overstated. However, diagnostic imaging is the largest source of human-made ionizing radiation exposure. Although dental diagnostic imaging constitutes less than 1% of the exposure, dental professionals have an ongoing ethical responsibility to keep patients’ exposure to radiation as low as possible (Benn & Vig, 2021). BIOLOGIC EFFECTS OF RADIATION The use of x-radiation for diagnostic imaging is essential for proper patient diagnosis and treatment. Dental radiographic examinations are fundamental to the daily practice of dentistry. However, x-rays are a highly energetic form of electromagnetic radiation that, like gamma rays and ultraviolet light, are capable of damaging human tissue. It is therefore important that dental professionals bear in mind what actually takes place when they expose patients to x-radiation. Each time a radiograph is exposed, x-ray photons exit the tubehead, penetrate the patient’s tissues, and expose the image receptor. However, not all x-ray photons reach the receptor; some pass through, and some are absorbed by the patient’s tis- sues, while others are deflected from their path and scattered in various directions. Ionizing radiation such as that produced from dental x-rays can cause changes to any component of a cellular membrane or the DNA that composes the cell’s chromosomes and that directs the cellular function via the production of free radicals (Geha, 2022). The consequences of the absorption of x-ray energy by human tissue are referred to as the biologic effects of radiation. Radiation biology is the study of these effects on living systems.
RESPONSE OF HUMAN TISSUE TO RADIATION EXPOSURE
Source: Bushong, S. C. (2013). Radiologic science for technologists: Physics, biology, and protection (10th ed.). Mosby.
Figure 1
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