Humans do not stay completely deprived of radiation. Nature emits a very small amount of radiation and many other things that leaves the human vulnerable to radiation.
In dental x-rays, humans are only exposed to an average of 0.005 to 0.01 mSv, where the average dose per person on the Earth is 2.4 mSv.
In fact, you would have received significantly more radiation on your flight on your last holiday than you would have at your last dental examination.