Depends where the damage is. Skin is made mostly of epithelial cells with a limited lifespan. Genetic damage to individual cells isn't lifetime- it goes away

Depends where the damage is. Skin is made mostly of epithelial cells with a limited lifespan. Genetic damage to individual cells isn't lifetime- it goes away when the cell dies. The damage a damaged cell can do is significant, though. But those cells are grown from stem cells, and if they remain undamaged, their descendants (the brand-new epithelial cells making up skin) will begin their life already damaged. With all that said, the underlying biology of cancer is extremely complicated and it's hard to evaluate the impact of things like this. Some amount of DNA damage happens constantly that bodies can clear up without any real long-term impact. For a dentist visit, we assume that the increased benefits from infrequent x-rays exceed the low probability of cancer. I don't know about UV used in dental applications, though.