Nettypoho, I seriously doubt that these rubber trays will affect mouth damage, as the radiation can easily penetrate them. I do, however wear the bottom one during my radiation treatments because after having some teeth pulled, the remaining ones do not line up exactly right, and the pressure the mask puts on them is uncomfortable, and probably not good for the teeth. Thus the guard, which works wonderfully well. I certainly hope your dentist knows something I don't!
Joanna