A great dentist who focuses on cancer patients is 100% critical, IMO. It takes a little work but once you've finished, you don't have to do it again.
For a good dentist who knows about cancer, I would ask all your oncologists first. Ask which dentist they would go to, or send a loved one to, in your situation. Explain you want the best care. Then would ask your family practice/regular doc that you are familiar with (if you have one) if they know of any good dentists who could help you.
Get several names if you can, then look them up & call each dentist office. Ask the receptionists specific questions about the dentists capabilities/history -- this was a great strategy for me as it led to me talking to several dentists directly over the phone for free before making any appointments! Ask about insurance. Check your insurance policy's website and be sure who you pick is covered. (Fluoride trays are "cosmetic" w/ our insurance so we have to pay for that.) Look online only AFTER you get the name from a trusted source, not before (saves time.) Any time a new issue came up this year, we've used this strategy to get to the next doctor we needed.
We drive 2.5 hours to see my husband's dentist in KC because we know he is the best. We love him. Here's a page that kind of shows why he's special and not the typical dentist most people see. Not advertising, by the way! Just sharing Hope that's allowed.