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Radiation doses in dental radiology

FAQs for health professionals

» What is meant by radiation dose of X-rays?

Radiation dose is a measure of how much energy is absorbed when something or someone is exposed to X-rays. This is important because it is this absorption of energy that can cause damage to a person. There are two commonly used ways of talking about radiation dose in dental procedures: dose estimated at the patient’s skin surface (correctly known as “entrance surface air kerma”) and effective dose. Dose estimated at the skin surface is easier to measure and is used in national surveys of X-ray equipment. Effective dose is complicated to calculate but the value can be related directly to radiation-associated risk.

» What unit are used for “dose” of X-rays?

The unit of entrance surface air kerma is the gray (Gy), but in dental radiology the dose levels are usually a small fraction of one gray (milli gray; mGy or even micro gray). In panoramic radiography, the different way in which the equipment works means that it is more sensible to use another quantity, not mentioned above for reasons of simplicity, that is, the kerma x area product (mGy.cm2). The unit of effective dose is the sievert (Sv). In dental radiology doses are fractions of a Sievert (milli sievert, mSv, or micro sievert, µSv).

» What is a typical dose from a dental radiological procedure?

Mean values from various national surveys are in the following ranges:

  • 1-8 mGy in terms of entrance surface air kerma for intraoral radiography; 
  • About 100 mGy.cm2 in terms of kerma-area product for panoramic radiography; 
  • 0.25-7 mGy in terms of entrance surface air kerma for cephalometric radiography.

As yet, there are no corresponding national survey datasets for CBCT.

Effective doses are:

  • intraoral dental X-ray imaging procedure 1–8 μSv; 
  • panoramic examinations 4-30 μSv; 
  • cephalometric examinations 2-3 μSv;
  • CBCT procedures 34-652 μSv,(for small dento-alveolar volumes) and 30-1079 μSv, (for large “cranio-facial” volumes). 

Thus the doses from intraoral and cephalometric dental radiological procedures are lower, usually less than one day of natural background radiation. Doses for panoramic procedures are more variable, but even at the high end of the range are equivalent to a few days of natural background radiation which is similar to that of a chest radiograph. CBCT doses cover a wide range, but may be tens or even hundreds of micro Sv of effective dose higher than conventional radiographic techniques, depending upon the technique. Rapid technological improvements to CBCT equipment mean that typical dose ranges are likely to change.