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Correct Answer: extraoral radiographs.
during dental x-rays, various types of radiographic examinations are used to visualize different aspects of the teeth and jaws. the type of x-ray dictates whether certain protective measures, such as the use of a thyroid collar, are necessary. the thyroid collar is a lead or lead-equivalent shield that wraps around the neck to protect the thyroid gland from radiation exposure. the thyroid gland is sensitive to radiation, and unnecessary exposure can increase the risk of thyroid dysfunction or cancer.
for intraoral radiographs, which include types like periapical, bitewing, and occlusal films, the x-ray source and film are placed inside the mouth. these types of x-rays focus on capturing details of individual teeth or groups of teeth. because the beam of radiation is directed towards a very localized area inside the mouth, there is a potential risk that the scattered radiation could reach the thyroid gland. therefore, the use of a thyroid collar is recommended to minimize this risk and protect the gland.
however, for extraoral radiographs, such as panoramic or cephalometric x-rays, the situation is different. in these procedures, the x-ray source and the film or detector rotate around the outside of the patient’s head. these x-rays are designed to capture larger areas or the entirety of the facial structure, not focusing intensely on any area that would direct radiation towards the thyroid gland. as such, the design of these machines and the nature of the exposure generally ensure that the thyroid gland is either outside the primary beam or exposed to very minimal radiation.
this understanding leads to the practice where a thyroid collar is not typically used during extraoral radiographic procedures. the decision not to use a thyroid collar in these scenarios is based on the low risk of thyroid exposure combined with the practical aspects of carrying out these types of x-rays. using a thyroid collar in extraoral procedures could interfere with the positioning and quality of the images obtained, which are crucial for effective diagnosis and treatment planning.
it is important to note that while the thyroid collar is not used for extraoral radiographs due to the reasons mentioned, all dental x-ray procedures must still adhere to the alara principle (as low as reasonably achievable), which aims to minimize the radiation doses and reduce exposure to as little as necessary by using appropriate shielding, proper equipment, and optimal techniques. this approach ensures patient safety while achieving the diagnostic benefits of radiographic imaging.
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