I. Apply the Principles of Radiation and Health Physics and Hazards
A. Together, the kVp, mA, and exposure time dictate the characteristics of the X-ray beam. A higher mA, higher kVp, and a longer exposure time equal an increased density. A lower mA, lower kVp, and shorter exposure time equal a decreased density.
1. X-rays are small wavelength, high-penetrating waves. They are known as ionizing radiation for their ability to ionize molecules, a process that is very damaging to biologic tissues.
B. X-ray machines have certain safety features.
1. A metal housing on the outside is lined with lead or made from lead to prevent radiation leakage. 2. An aluminum fi lter just outside the X-ray tube fi lters out the nonpenetrating, longer wavelength
beams.
3. The unit must be outfi tted with a collimator that fi ts over the opening where the X-ray beam emerges from the machine. The collimator must be made from lead and the opening must not be more than 2.75 in in diameter. This limits the radiation emitted to no more than 2.75 in.
4. The PID is a device on the X-ray tubehead that aims the X-ray beam; PIDs are available in cylindrical and rectangular shapes, with rectangular shapes reducing radiation exposure.
C. Understand radiation physics.
1. Primary radiation are X-rays that came directly from the X-ray tube where they are generated. These are high-energy, short-wavelength beams that travel in a straight line from their source. In practice, this is often referred to as the useful beam.
2. Secondary radiation is created when the X-ray beam interacts with another substance—in this case, the patient’s tissues. Secondary radiation has less energy and longer wavelengths than primary radia- tion. It is not considered useful because it creates foggy or cloudy dental radiographs.
D. If malfunction of the X-ray machine is suspected, alert the dentist, and do not take any more radiographs until the machine is deemed safe.
II. Patient Radiographic Safety Practices
A. Unnecessary x-radiation exposure comes from secondary radiation, scatter radiation, and leakage radiation. B. Radiation causes biologic damage through ionization. X-rays are frequently called ionizing radiation because of their ability to interact with, and change, atoms. Thus, X-rays are capable of changing molecu- lar structures in the body, affecting organ tissues.
1. Damage occurs when individuals are either exposed to high levels of radiation suddenly (e.g., acute exposure) or exposed to low levels of radiation over a very long time (e.g., chronic exposure). Acute exposure can cause immediate cell death. At lower levels, the effect on cells, and therefore health, depends on the cell type. Radiation exposure can cause damage to the DNA located within somatic cells. Cell division may be prevented or compromised, resulting in damage to the organism. In contrast, genetic cells experience damage to the chromosomes carried within the cells and can be passed to future generations.
2. The period between radiation exposure and its biological effect is the latent period, which can be several years.
C. ALARA stands for “as low as reasonably achievable.” This means exposing patients and operators to the lowest possible dose of radiation that will get the job done. Dental radiographs should never be pre- scribed on a routine basis and should be based on clinical need. Today, most state regulatory agencies require documentation of need rather than radiographs being taken routinely.
D. Before any radiographs are ordered, a complete oral examination should be conducted and a patient history should be taken, including any medical conditions as well as previous exposure to X-rays. This information should weigh into the decision to prescribe X-ray imaging. Indications for dental radio- graphs include history of previous dental disease, positive clinical signs/symptoms, and increased risk of dental caries.
Radiation Health and Saf
ety
R ev i ew Q u e s t i o n s
32. What types of cells are most easily destroyed or altered? A. Bone cells
B. Brain cells
C. Blood-forming cells D. Nerve cells
33. A collimator is used to
A. reduce the size of the primary beam. B. remove attenuated radiation.
C. minimize patient exposure time. D. fi lter scatter radiation.
34. What do the letters in ALARA mean? A. As low as reasonably achievable B. As low as reasonably available C. As long as roentgens approved D. As long as reasonably available
35. What kind of radiation exposure causes damage slowly over time before the effects are noticed? A. Acute
B. Chronic C. Cumulative D. Natural
36. The use of a thyroid collar is contraindicated when exposing A. panoramic radiographs.
B. occlusal radiographs. C. intraoral fi lms on children.
D. intraoral fi lms on edentulous patients.
37. If the dental assistant suspects that the X-ray machine is malfunctioning, which of the following actions should be taken?
A. Adjust the collimator and continue with the series . B. Check the machine at the end of the day .
C. Immediately stop exposures and notify the dentist . D. Submit a written report to the offi ce manager .
38. The ADA guidelines recommend that radiographs should be taken how often? A. Every 6 months
B. Every 12 to 18 months C. Once every 2 years D. As necessary
39. What is another name for secondary radiation? A. Controlled
B. Short C. Scatter
Radiation Health and Saf
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40. All of the following cause unnecessary radiation exposure EXCEPT A. re-takes.
B. optimum fi lm processing. C. slow-speed fi lm.
D. scatter radiation.
41. Erythema, nausea, diarrhea, hemorrhage, and loss of hair are signs and symptoms seen with A. long-term effects of radiation.
B. short-term effects of radiation. C. cataracts .
D. primary radiation.
42. Which of the following components of the tubehead helps reduce X-ray exposure? A. X-ray tube
B. Metal housing C. Oil bath
D. Step-up transformer
43. Which of the following would result in the LEAST radiation exposure to the patient? A. Slow fi lm speed and high kVp
B. Slow fi lm speed and low kVp C. Fast fi lm speed and low kVp D. Fast fi lm speed and high kVp
See p. 55 for the correct answers and rationales