Modern dental x-rays are basically negligible for most patients, although not for dentists who do them daily, even though they're well away from the beam - which is why they have to hide when they take them.

Less negligible are CT scans, which can expose you to multiples of the average annual background dose in a few minutes.

That's still relatively low level exposure. But there isn't really a safe minimum exposure level, and it's certainly not something you'd want to have regularly.