The exposures of bone marrow to radiation during typical X-ray examinations are listed to the left in millirems, a measurement of radiation.
The maximum on-the-job yearly exposure for Canadian and U.S. radiation workers has been set at 5,000 millirems. Low doses spread out over a period of time are not as harmful as larger doses at once because the body has time to recover.
You would have to take 1750 dental X-rays to equal the radiation in a lower GI series! 1 dental X-ray is 1/10000 of the yearly maximum recommended dose.
To put things in perspective, each time you fly from coast to coast you receive 4 millirems of background radiation, or the equivalent of four panoramic radiographs.
As well, there is background radiation from concrete buildings, roads and even the sun! Just standing around you receive more than 3 bitewing X-rays worth of radiation every day.
We would have to take almost 10,000 dental X-rays to reach your maximum safe yearly dose!
When you weigh this against all the serious conditions such as decay, periodontal disease, abscesses and cancer that can go undetected without X-rays, it seems like a pretty fair tradeoff.