Do I need those dental x-rays?

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Xray of lower molar teeth showing many possible problems causing pain and infection

It is not unusual for patients to ask us about whether dental x-rays are safe. Good periodontal diagnosis frequently involves us taking anything from two to twelve dental x-rays and this is sometimes a cause for concern. When we plan our dental implants we frequently refer patients for a special low-radiation type of scan called a cone-beam CT scan. To add to the fears about the risks, the media are quick to publish data suggesting increased risks of various tumours from dental radiography. One recent study (1) for example, reported a risk between dental x-rays and meningioma (a type of brain tumour). Below I discuss the reasons why the findings from this study could be questioned, but before I do that, lets look at a few facts:

Dental x-rays are an essential part of our armamentarium. They help us make good diagnosis which avoids risks of pain, infection or further dental disease for the patient. They help us avoid making guesses and subsequent mistakes when treating our patients. Dental x-rays produce such a small amount of radiation that it is difficult to measure the risk. We can compare a dental x-ray’s radiation exposure to the amount of radiation received from space when taking a short flight. Estimates suggest that this exposure relates to a maximum risk of one in two million of causing a fatal tumour (7). We are constantly bombarded by radiation from the natural world around us – resulting in an annual exposure of 2,400 microSieverts (the unit of radiation exposure). A single dental x-ray carries a maximum exposure of a mere 5 microSieverts – more or less the same radiation exposure as living for another day on planet Earth.

Notwithstanding these facts, we take the exposure of our patients very seriously and adopt the following measures to minimise their exposure.

  • We always weigh up the benefit from taking the x-ray versus the potential risk and only take x-rays if we have a good reason for doing so (5,7).
  • We do not take any x-rays as part of a standard programme; every patient is individual and we consider their needs before making an exposure (6,7).
  • When receiving referred patients we do our best to obtain their recent x-rays from the referring dentist to reduce the need to make further exposures ourselves (7).
  • We use a state of the art digital imaging system which is very sensitive and needs very little exposure to create a good image.
  • We take and process each image carefully to avoid the need to take another one (7).
  • Finally, we ensure we get the benefit from the images by examining them with care.

What about that meningioma study?

We must be very careful when interpreting medical literature; what is presented as science can sometimes be interpreted in a completely skewed way by the media in order to create a good story. This particular study verbally asked patients with meningioma whether they remembered having any dental x-rays. They matched these patients with healthy individuals of the same age and gender and asked these latter about their exposure to dental x-rays. The meningioma group reported more dental x-rays being taken and this was taken as as association between dental x-rays and development of this tumour. Unfortunately as is the case in many association studies – the association is not necessarily a demonstration of causation.

First of all – certain factors such as for example cigarette smoking or an unhealthy diet could be factors leading to dental disease (resulting in a need for dental x-rays) and also influence the development of a tumour. The tumour and the dental x-rays are associated in the same people, yes, but not because one caused the other. Rather they were both caused by something else! Secondly – a meningioma may cause symptoms of pain and discomfort in the teeth and jaws before they are diagnosed (2 and 3). This could encourage the patient to see the dentist who would naturally get some x-rays to find out what is wrong. Here we have a situation where the tumour causes the x-ray to be taken and not the other way about! Finally,  it is debatable whether asking someone to remember whether they had any dental x-rays is a reliable way to collect information – if they have a brain tumour they may be more likely to want to place the blame somewhere and remember the dentist’s xrays.

To further add to this picture lets compare the brain radiation exposure from four dental x-rays (0.07 mGy) versus that of a head CT scan (50mGy) – about 700 times as much! Studies have tried and failed to show a link between head CT scans and brain tumours (4) showing that even at these comparatively high levels of radiation exposure, it is not really possible to find a definite link between x-rays and brain tumours.

References

  1. Claus EB, Calvocoressi L, Bondy ML, Schildkraut JM, Wiemels JL, Wrensch M. Dental x-rays and risk of meningioma. Cancer. 2012 Apr 10. [Epub ahead of print]
  2. Bullitt E, Tew JM, Boyd J. Intracranial tumors in patients with facial pain. J Neurosurg. 1986;64:865-871. Abstract
  3. Cook RJ, Sharif I, Escudier M. Meningioma as a cause of chronic orofacial pain: case reports. Br J Oral Maxillofac Surg. 2008;46:487-489. Abstract
  4. Phillips LE, Frankenfeld CL, Drangsholt M, Koepsell TD, van Belle G, Longstreth WT Jr. Intracranial meningioma and ionizing radiation in medical and occupational settings. Neurology. 2005;64:350-352. Abstract
  5. International Commission on Radiological Protection. Radiological Protection in Medicine. Ann ICRP. 2007;37:ICRP Publication 105.
  6. American Dental Association Council on Scientific Affairs. The use of dental radiographs: update and recommendations. J Am Dent Assoc. 2006;137:1304-1312. Abstract
  7. European Commission. Radiation Protection. European guidelines on radiation protection in dental radiology: the safe use of radiographs in dental practice. Issue No. 136.http://ec.europa.eu/energy/nuclear/radioprotection/publication/doc/136_en.pdf Accessed 30th November, 2012.

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