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It is well known that the thyroid gland is highly susceptible to radiation and exposure to ionizing radiation has been shown to cause thyroid cancer.

Definite increased cancer risk

Experts from Cambridge University evaluated the exposure of those with thyroid cancer to dental X-rays in the Kuwait Cancer Registry to determine the risk posed by these X-rays. When those who had undergone dental X-rays were compared to those who had never received X-rays, the risk of thyroid cancer more than doubled.1 The most common types of cancer found were papillary and mixed papillary/follicular types of thyroid cancer. These findings support other studies that found an increased risk of thyroid cancer in dentists, dental assistants(13 X higher risk), diagnostic x-ray workers, and radiology technologists.2-7

Does it matter if the X-rays are digital?

Digital X-rays have been used for some time instead of conventional X-rays that need to be developed. The amount of radiation with digital X-rays is 50 to 80% less than for traditional X-rays.  It was not known if the majority of X-ray exposure was from digital or conventional X-rays in the Cambridge study. Unfortunately, experts have found that some dentists are inclined to take more digital X-rays because of ease of use and diminished radiation exposure offsetting some of the benefit of using this newer technology.8

What should you do?

The amount of radiation from newer X-ray technology and the scatter of radiation from the mouth to the nearby thyroid may be minimal. In fact, a single set of digital dental X-rays provides much less than the normal daily background exposure to radiation that occurs naturally in the environment. However, any excess radiation should be avoided and wearing a lead lined thyroid guard seems reasonable in light of the high sensitivity of the thyroid gland to radiation, the closeness of the thyroid gland to the areas being X-rayed, and the known association of ionizing radiation with thyroid cancer.

 


References

  1. Memon A, Godward S, Williams D, et al. Dental X-rays and the risk of thyorid cancer: a case-control study. Acta Oncol 2010; 49: 447-453.
  2. Wingren G, Hallquist A, Hardell L. Diagnostic X-ray e xposure and female papillary thyroid cancer: A pooled analysis of two Swedish studies. Eur J Cancer Prev 1997;6:550 –6.
  3. Wingren G, Hallquist A, Doberman A, Hardell L. O ccupation and female papillary cancer of the thyroid. J Occup Environ Med 1995;37:294 –7.
  4. Hallquist A, Hardell L, Degerman A, Boquist L. O ccupational exposures and thyroid cancer: Results of a case-control study. Eur J Cancer Prev 1993;2:345 –9.
  5. Wang JX, Boice JD Jr, Li BX, Zhang JY, Fraumeni JF Jr. Cancer among medical diagnostic x-ray workers in China. J Natl Cancer Inst 1988;80:344 –50.
  6. Wang JX, Inskip PD, Boice JD Jr, Li BX, Zhang JY, Fraumeni JF Jr. Cancer incidence among medical diagnostic X-ray workers in China, 1950 to 1985. Int J Cancer 1990;45: 889–95.
  7. Zabel EW, Alexander BH, Mongin SJ, Doody MM, Sigurdson AJ, Linet MS, et al. Thyroid cancer and employment as a radiologic technologist. Int J Cancer 2006;119:1940 –5.
  8. Berkhout WE, Sanderink GC, Van der Stelt PF. Does digital radiography increase thenumber of intraoral radiographys? A questionnaire study of Dutch dental practices. Dentomaxillofac Radiol 2003; 32: 124-127.

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