Routine dental X-rays are not backed by evidence

I am all for evidence-based medicine making its way into dentristry if it's lacking... but if you're someone who is worried about cumulative exposure to X-ray length radiation, what is the dosage? And can we compare it relative to to say, millimeter scanners at the airport or a domestic flight?

I was under the impression that the digital machines they use these days are:

1. localised 2. very, very low dose

My dentist said something like "it exposes you to less radiation than eating a banana", but she also left the room when the machine was firing.