Use of radiation in health care
X-ray examinations of the teeth and face are a dentist’s important tool for diagnosis and follow-up of treatment. Different types of X-ray examinations of the teeth are performed at approximately 2,000 locations around Finland.
The number of dental X-ray examinations is high compared to the number of all X-ray examinations, but they concern a small region and cause a relatively small radiation dose to the patient. X-rays are always taken at the dentist’s discretion and decision, and they are not made routinely without a patient-specific consideration of necessity.
Dental X-ray appliances
Dental X-ray examinations are performed using a dental X-ray device that images using an intraoral image sensor (intraoral X-ray device), panoramic radiography devices and cephalostats and cone beam computed tomography systems (CBCT device).
In an intraoral X-ray device, the image is recorded on film or digital image sensor placed inside the mouth. The device is used for imaging individual or a few adjacent teeth. The radiation dose caused to the patient from one image is around 0.01 millisievert (mSv), which equals approximately 24 hours’ exposure to environmental background radiation. The recent digitalisation of dental X-ray equipment has decreased the radiation dose from intraoral imaging in particular. There are approximately 4,800 intraoral X-ray devices in use in Finland, and the annual imaging volume is approximately 2.3 million images.
In a panoramic radiography device, the radiation source, or the X-ray tube, and image scanner rotate diametrically in a semicircle around the patient’s head, which makes it possible to image all teeth in a single image. It is important from the point of view of the photo succeeding that the patient is positioned correctly using the indicator lights in the device. The radiation dose in panoramic imaging is approximately 0.02 mSv, equal to the environmental background radiation exposure during a couple of days. There are approximately 700 panoramic radiography devices in use in Finland, and they currently perform approximately 400,000 examinations a year. A cephalostat can be added to the panoramic radiography device, if necessary. Cephalostat is an additional head-positioning device used when taking lateral images of the skull. These images can be used for assistance in orthodontic treatment, for example. The radiation dose from a single lateral cranial image is under 0.01 mSv.
In oral X-ray examinations, the thyroid gland is the most important organ to be protected from the point of view of protecting the patient from radiation. The thyroid gland is protected by a special lead collar if it does not interfere with the actual examination. Lead protection for shoulders can be used in panoramic radiography. A foetus’ exposure to radiation in dental X-ray examinations is very low. A lead apron placed on the abdomen therefore does not have a significant shielding effect, but one may be used.
The need for radiation protection in the imaging room is influenced by, for example, the frequency of use of the X-ray appliance, radiation output of the device, size of the radiation beam and imaging directions, as well as the location of the X-ray device in the room and the purpose of use of the rooms surrounding the imaging room. In the case of intraoral and panoramic devices, the existing structures of the room (such as brick walls) are in many cases sufficient structural radiation protection. If the structures are deemed to be insufficient, the radiation protection of walls or parts of the walls has to be strengthened.
Employees performing dental X-ray examinations must protect themselves from radiation. The minimum distance from the patient and the radiation source in intraoral and panoramic tomography imaging is two metres. Moving behind a partition wall for the duration of imaging is usually sufficient radiation protection.