People are talking about x-rays as if they are simply a test for cavities. They serve other purposes.
I get an annual dental checkup (military) with the around-the-face x-ray machine. The first thing the dentist does is to compare it to last year's scan. The x-ray allows them to spot all sorts of things they would otherwise miss, especially since I don't think I've ever seen exactly the same dentist twice. Teeth move. Teeth wear down or chip. Sometimes this can be spotted by eye but the x-ray record is more reliable and more easily communicated between offices.
As for radiation, if you are worried about an annual dental x-ray then you better not fly in an airplane, live in Colorado, or hang around too long near the bananas at the grocery store.