Hi Anita,
I strongly suspect he is using Gel-Kam, HUP reommended, or some other .4 stannous flouride which does cause major discoloration of the teeth. This is what I use and my teeth are darker than when I was a cigarrette smoker. I get mine cleaned and polished every two months by my periodontist. There is a 1.1 some other type of flouride that is not supposed to stain as badly but it is also not supposed to be as effective. Thus far, I have not found any brand available in our area. I did have my teeth professionally whitened by my prosthodontist and it was after that that I started to develop all sorts of cavities eventually leading me to have all my teeth capped (I only have 12, they pulled the others before rads). My dentist says no relation and he is a MDA graduate so should know but I wonder if the bleach on the radiated teeth was just too much. Clark does need to keep using his trays if he wants to keep his teeth. Maybe see if you can find some of that other flouride that doesn't stain as badly. If you do, let me know the brand.

Take care,
Eileen