More on X-ray

The most common dental X-ray, the bitewing radiograph, exposes you to 0.038 mSv, and a full-blown dental X-ray examination is only 0.150 mSv.

That's on the old film X-rays though, Digital Dental X-rays can be up to 1/3rd to 1/4th   less than even the traditional dental x-ray.

Compare that to how much radiation you are exposed to from space every year: 0.510 mSv, and how much from nature: 3.000 mSv.

Source
Estimated Exposure (mSv)
Man MadeDental X-raysBitewing radiographs
Full-mouth series
0.038
0.150
Medical X-raysLower gastrointestinal tract radiography
Upper gastrointestinal tract radiography
Chest radiograph
4.060
2.440
0.080
NaturalCosmic (Outer Space) RadiationAverage radiation from outer space In Denver, CO (per year)
0.510
Earth and Atmospheric RadiationAverage radiation in the U.S. from Natural sources (per year)
3.000