When we were TTCing I fell rather badly and it was thought I had broken my tailbone. Because we were in the 2WW the x-ray place made us wait until we knew for certain before they would scan me. The radiographers I spoke to said that they personally wouldn't take the risk.
But saying that, that x-ray was right near the important bits, and like Freya said dental ones don't emit that much radiation.
Can you ring the place that you are booked into to check?