The fluoride trays are not the same as the fluoride treatment that kids get at the dentist’s. The head and neck cancer patient is advised to use the trays (which are like mouth guards with fluoride in them) for ten to 15 minutes before bedtime. It’s a long term preventative measure. My husband had really good teeth prior to radiation but he eventually slackened off after his radiation treatment (his complaint was he was having to put too many things in his mouth every night) and he promptly started getting dental decay and required root canals. Apparently the radiation did a number on the enamel.