The flouride trays are a must. The teeth can literally rot out of a person's mouth after radiation. Another board I am on just had a post from someone who is experiencing that because no one told him about the need for flouride.
Like Dinah I couldn't use mine right away because my mouth was too sore. In the meantime I brushed with a foam brush and used various oral rinses and a baking soda solution. I've been using the flouride for about 8 months now and thankfully my teeth seem to be in good shape. My dentist has had other patients who have had radiation and he is very familiar with the special concerns. Excellent dental care is very important post radiation. I also have a very skilled and patient hygenist who can deal with my inability to open my mouth very wide.