Sieverts- They Used To Be So Rad....

Remember how those twisted microbiologists had a beer-soaked conference in Gstaad (Gum Tissue Is The Issue, April 2009) and drove us students of all things dental positively mad by arbitrarily re-naming the germs that cause periodontal disease? Well, someone had their hands in the Cookie Jar of Arbitrary Nomenclature Changes again, because while I wasn't looking, they took the units of radiation exposure, Rads, and changed them all to Sieverts. Why oh why do they tax our brains so? It's bad enough to face all those other taxes... But I digress.

As a practicing dentist who sometimes encounters resistance to the taking of diagnostic X-rays, and as a person who hasn't flown in awhile but is astonished by those X-ray scanners that the TSA imposes, without consent, on travelers who use airports, I thought it would be instructive to compare radiation doses from lots of stuff. I won't editorialize. Much. I'd rather leave you to draw your own conclusions. I should say though that the scanners amaze me- they are used without formal consent. You're forced to go through them if you're going to fly that day. In Pennsylvania law, if we subject a competent patient to any invasive procedure on their body without their consent, it's called battery and it's breaking the law. I suppose there are alternatives so that going through a scanner is not forced. All I can think of is not flying and taking the bus instead. Which is difficult if your destination is Marseilles. Do they give you other alternatives? A voluntary strip search? Writing a term paper? I haven't flown recently enough to know.

Of course we are balancing essentially involuntary radiation exposure against national security concerns, and it is a case of "The needs of the many outweigh the needs of the few. Or the one." It's just a strange and alien thought process for a dental practice like ours that asks, "May we take an X-ray of this area today?"

So- let's do the numbers. A "mSv" is a milli-Sievert, one thousandth of a Sievert.

Also- big point- whole body exposure is a very different thing than a diagnostic film of just one part of us. So a seven hour airplane flight "equals" three dental panoramic X-rays, but not really because only a particular part of one's head is exposed for the dental image.

Here we go:

3 mSv/year or 0.01mSv/day: natural background radiation.

0.02 mSv: Additional exposure from a 7 hour airplane filght, because you are above much of the Earth's protective atmosphere which shields us against cosmic radiation. And because airplanes are made largely of aluminum, not a great insulator against radiation. Then again, planes made of lead don't fly very well.

2.2 mSv/year: Additional radiation exposure experienced by commercial airline pilots and crew. So, their occupation almost doubles their background radiation exposure.

2.2 mSv: Brain CT Scan. Same as the flyers, but not whole-body.

7.0 mSv: Chest CT Scan.

0.001 mSv: Backscatter Wave Scanner at airport security. Supposedly- I'd like to see independent data, not just government quotes. Still, it wouldn't be off by a factor of 10, so the scanner gives you about 1/20th the exposure of the flight itself. Supposedly. ***As of 11/2010 the government has not allowed any independent research facility to measure the radiation form a Backscatter Wave Scanner, according to Dr. Dvid J. Brenner (Higgins Professor of Radiation Biophysics, Columbia University): http://www.npr.org/2010/11/19/131447056/are-airport-scanners-safe

0.1 to 0.5 mSv: Chest X-ray. So, in principle, it would take 100 airport TSA scans to equal one chest X-ray.

0.1 to 0.2 mSv: Skull X-ray.

0.6 to 1.7 mSv: Abdomen X-ray.

3.0 to 8.0 mSv: Barium X-ray.

2.0 to 4.0 mSv: Head CT Scan.

5.0 to 15.0 mSv: Body CT Scan.

Now for the teeth:

0.084 mSv: Full mouth series of X-rays, D-speed film. (Recommended every five years)

0.033 mSv: Full mouth series of X-rays, F speed film and digital with phosphor plates or sensors. Digital is often even less.

0.17 mSv: Bitewing X-rays, D-speed film. (Recommended eachyear, four films)

0.007 mSv: Bitewing X-rays, F-speed film and digital. Digital is often even less.

0.007 - 0.014 mSv: Panoramic study, shows the entire mouth but like mapping the spherical Earth there are distortions, so bitewings are used to supplement and gain detail between teeth.

0.005 - 0.038 mSv: Kodak K9000 3-D dental imaging scan (as used for individual teeth)