Ah, I don't want to start a war but.... Famous last words.
Although I don't think flouride trays are going to inspire quite the same passion as PEGs. I confess to an age bias as I loved the 1964 cold war black comedy spoof movie Dr. Stangelove. (plot below for younger posters)
[quote]US Air Force General Jack D. Ripper plans to start a nuclear war with the Soviet Union to stop what he believes to be a fearful Communist conspiracy to put fluoride in the water supply, by his reasoning, thereby threatening the "precious bodily fluids" of the American people.[/quote]
The toxicity of flouride is beyond question, but then so is the toxicity of the radiation most of us owe our lives to.
The amount in a tooth tray from a flouride gel does not pose any real danger, IMO. Of course, I trust my prothodontist, who has been able to keep all my teeth intact.
Tooth decay is a proven risk after radiation and flouride applications reduce that risk substantially.
I agree wholeheartedly with the subject line advice of this thread: Don't swallow liquid flouride rinse at dentist. I would expand it to say: Don't swallow your flouride gel from your tooth trays either. It's supposed to be a topical application not an internal one. Just like you would never eat or swallow antibiotic cream instead of taking an antibiotic pill
Here is a pretty universal summary of why and how to use your flouride trays
[quote] Fluoride Tray Method: Head and neck radiation patients are at a lifelong risk for tooth decay due to the reduction in their saliva and an increase in decay causing bacteria. Fortunately, using fluoride once a day can prevent this rampant decay. It will be necessary to not only use the fluoride trays during treatment but also for the rest of your life. You will need to have individualized custom made trays made by your dentist for your mouth. Your dentist will prescribe a fluoride gel, such as 0.4% stannous fluoride gel or a 1.1% neutral sodium fluoride gel preferably unflavored.

First floss and brush your teeth. Rinse and dry your fluoride trays and place a thin ribbon of fluoride gel covering the bottom of the trays. Dry your teeth with gauze or a soft cloth. Insert the trays and bite down holding the trays between your teeth for 5-10 minutes. The fluoride gel must cover the gumline as that is where you will be susceptible to decay. Many patients do this while showering or bathing to save time. After 5-10 minutes, remove the trays and spit out the fluoride.

Do not swallow the fluoride or rinse the fluoride out with water. You may wipe off the excess fluoride with a dry cloth or gauze. Do not eat or drink anything for 30 minutes. Always clean the trays after the fluoride treatment and put them in a clean container. [/quote]
Charm