Re: dental x-rays

[Ludwik Kowalski <KowalskiL@MAIL.MONTCLAIR.EDU>]

SOME PEOPLE HAVE NOTHING BETTER TO DO THAN
TO INVENT NEW UNITS!

Some of us do not automatically remember that:

1Gy (dose of one Gray) is when 1 kg of body tissue absorbs
1 joule of energy. The older unit of dose, 1 rad, is the same as
0.01 Gy or 10 mGy.

For x rays one can assume that 1 rem=1 rad (or 1 Sv = 1 Gy).
Therefore:

Dental bitewing (4 films) 0.038 milisievert (mSv) --> ?

0.038 mSv = 0.038 mGy = 0.0038 rads = 3.8 mrads = 3.8 mrem

or roughly 1 mrem per film. In other words, what we receive from
this 4-films procedure is about 2% of what every part of our body
receives in one year from the environment. I am assuming the yearly
dose is 200 mrem. Brian quoted (see below) the average yearly
dose of 3600 mSv (360 mrad). This probably accounts for medical
treatments. Right? Otherwise 360 is about two times larger than what
is usually printed for the so-called "natural background."
Ludwik Kowalski

brian whatcott wrote:

> I see Steven Ratcliff's 100 mrem and raise him 150 microSievert and
> 1 microGray: - or to put it another way:
>
> The Health Physics Society provided this potted answer on their web page:
>
> Answer to Question #259 Submitted by Ron Sumner
> Category: Medical and Dental Procedures
>  The following question was submitted on April 11, 2000,
> and was answered by an expert in the appropriate field:
>
>  Question:
> My wife recently had a dental exam with xrays,
> and we just found out that she was probably about three
> weeks pregnant at the time. Where can I find information about
> the risks involved? Thanks.
>   Answer:
> When a pregnant patient undergoes a complete
> dental x-ray examination, the radiation dose to the embryo is
> about 1 microgray. Compare this to the average dose from
> naturally occurring environmental sources of about 3000
> microgray per year. Thus, the dose from the dental examination
> is less than that from one day of environmental exposure.
>
>  There are no data demonstrating any risk from
> such doses. While the absence of data does not provide
> conclusive proof of total safety, it does provide assurance that the
> risk, if any, is exceedingly small.
>
>  <http://www.hps.org/publicinformation/ate/q259.html>
> -----------
> By contrast, this Trexler Practice web page takes a different view:
>
>     How often are dental X-ray exams necessary?
>
>      This depends on the patient’s individual health needs. If you are a
> new patient, the dentist may recommend X-rays to determine the current
>  status of your mouth and to check for hidden problems. The schedule
> for needing radiographs at recall visits varies but typically includes
> 2-4 bitewing X-rays per year. Full- mouth series and/or panoramic films
> are typically taken every 3- 5 years. Children may need X-rays more
> often than adults because their teeth and jaws are still developing and
> they are more prone to tooth decay.
>
> How much radiation is involved in a dental X-ray exam?
>
> Using effective dose equivalents, environmental exposures may be
> compared to exposure from dental X-ray exams. Applying this method,
> a full mouth X-ray examination of 19 films will deliver an effective
> dose equivalent of approximately .15 mSv or 15 days of exposure to
> naturally-occurring environmental radiation. The chart below lists
>
>  comparisons of common sources and amounts of radiation:
>
>   Activity / Source
>                                             Amount of Radiation
>                                                  Received
>         Bitewing (4 films)
>
>                                           0.038 milisievert (mSv)
>
>         Full-mouth Series (19 films)
>
>                                           0.150 mSv
>
>         Lower GI series
>
>                                           4.060 mSv
>
>         Average U.S. citizen living in average
>         location
>
>                                           3.600 mSv annual dose
>
> <http://www.trexlerdental.com/xrays.htm>
>
> ***********************************************