Documentation: Radiation Equivalent Dose

Patient Radiation Doses from Intraoral Dental Radiography.

From Radiation Protection in Dentistry
National Council on Radiation Protection and Measurements
NCRP Report No. 145
Issued Dec. 31, 2003

The table above gives the effective dose to the patient when taking FMX and BWX surveys:

 

A Full Mouth series of X-rays (FMX) consists of 14 to 21 films (averaged)

A Set of Bitewing X-rays (BWX) consists of 2 or 4 films (averaged)

Separate values are given for both D speed films and E speed films

Table shows short cones, long cones, and long rectangular cones

Values are in µSV which is millionths of a sievert rather than mSV

To convert µSV to mSV, move the decimal point three places to the left

Thus 3 µSV becomes .oo3 mSV and 150 µSV becomes .150 mSV

To convert µSV to mREM, move the decimal ONE place to the left

Thus 150 µSV becomes 15 mREM

1. There are very few short cones left in service in The US or Europe.  They are considered unsafe due to the larger amount of scatter they produce. (See the table above).

2. Most operators use round, long cones.  They provide more parallel rays, and their better collimation reduces scatter to the patient. 

3. *Bisecting angle techniques can be done with long cones as well as with short cones, and with much less radiation to the patient.

4. Rectangular cones are available.  They reduce the effective dose to the patient greatly.  The reason they are not more widely used is that the beam diameter is small and cone cutting is a more frequent error.

5. Very few x-ray machines today have easily adjustable kVp or MA.  The exposure is controlled exclusively by a timed pulse.  Most dental machines are set at or around 70 kVp

Estimated Average Annual Effective Dose of Ionizing Radiations to a Person in the United States

Other

From Frederiksen NL. X-Rays: What is the Risk? Texas Dental Journal. 1995;112(2):68-72

This chart shows the averaged annual dose of Radiation received by a person in the US broken down by categories.  Note that the total average exposure to the average person from medical and dental procedures amounts to 3.00 mSV while the amount of radiation from natural sources is about 0.60 mSV

You can also use this excellent web page from the American Nuclear Society to calculate your own yearly exposure from all sources of ionizing radiation.