That's what I was led to believe by my dentist when I asked. I just checked danish national guidance, and they say the dose of x-rays is so low the increased risk is incalculable. Instead they say the dentist should only ever use an x-ray if they find it medically necessary out of a principle of minimization.

So it sounds like it's the individual dentists judgment, and their organizing body says that they base it on the occurrence of dental problems in the population the clinics they oversee, with some adjustments based on patient age and risk factors.

So according to Danish authorities, you should be safe getting x-ray'ed every 6 months. They just don't recommend it, since it's a waste.