Answer to Question #10794 Submitted to "Ask the Experts"

I just had a root canal and now I am in the process of getting the crown. I am also getting braces. My concern is that in the past 10 days I've had a total of 10 x rays on the tooth involved in the root canal and a panoramic x ray from my orthodontist. Four of the tooth x rays, as well as the panoramic x ray, were done with the new computerized machines. Six of the other x rays were done with a machine from the 1980s. My regular dentist has not upgraded to the newest technology. I am concerned that this radiation exposure could lead to brain tumors or other health concerns. I still have to go back to my dentist to put the permanent crown and there may be more x rays to come.

Thank you for your two-part question regarding machines and patient dose.

Regarding machines: Dental x-ray machines, whether of older (for example, the 1980s) or newer vintage, should be regulated by your state health department, and should be required to be inspected periodically by a physicist or technician to confirm that (a) each machine is generating the proper spectrum of x rays, (b) the timer is accurate, and (c) no unacceptable leakage of radiation is occurring.

Noncompliant machines must be repaired before they are used again. Regardless of the development of new technologies in x-ray machines, such as computerized controls, the new machines generate, for safety purposes, the same x-ray beam as the older machines and therefore should essentially deliver the same dose of x rays to the patient.

Regarding dose: Each dental x-ray image made results in a small deposition of energy within the patient. This is called “absorbed dose.” Absorbed dose to the patient from dental x-ray imaging, even if dozens of images are made, is very small compared to other x-ray exposures made for medical purposes.

If there is a biological risk to patients from dental x rays, this risk is for neoplasms (benign or malignant tumors) of various tissues, including the brain, salivary glands, and bone marrow. I say “if” because there is a healthy disagreement among experts as to whether such small doses actually result in an increased likelihood of neoplasms.

The body has DNA repair mechanisms which may sufficiently overcome the damage from such small doses to prevent progression of the chain of events resulting in the development of a neoplasm. If there is indeed such a risk, it is conservatively estimated to be within the range of 0.5 to 1 fatal cancers from a million single-intraoral exposures, and between 0.3 and 1.3 fatal cancers from a million panoramic exposures. This is a very small risk; we accept much larger risks from this several times per week in our daily lives. A “full mouth” dental image series typically consists of 20 exposures, and so having had 10 such exposures recently is not extraordinary. You should weigh this estimate of risk against the risk(s) that would follow from proceeding with your treatment without the image(s) in question.

Your dentist should be able to explain to you exactly why a particular image is needed, and should avoid making images that are not essential. I suggest discussing your concern with your dentist and ask him or her to use the fastest available image receptor (either E or F speed film, or a digital sensor) to minimize your absorbed dose. Some dentists also use a device called a “rectangular collimator” for making intraoral images that further reduces absorbed dose.

A journal article summarizing the absorbed dose and risk considerations is in the Journal of the American Dental Association (Ludlow JB, Davies-Ludlow LE, White SC JADA 139:1237–1243; September 2008).

S. Thomas Deahl DMD PhD