bad breath chronic halitosis?

bad breath cures
Claudiu asked:

I have a friend he is 16 years old.
Hes breath smells extremly bad especialy when we are in a tight place like bus or something hes smell go like a few meters even other people feel it.
He knows he has bad breath and tryed everything to cure it:
1. by himself at home cleaning 3 times+floss+tongue +water with salt for tongue + on bus parsley/gum(Orbit/Winterfresh/and others) EXTREMLY MUCH WATER he drinked water like each 30 seconds in bus
2.He got to dentist no luck….
I really want to help him as hes my best friend.
Also I don’t know if it matters but hes breath smells very bad when he breaths on nose He don’t need to talk to feel hes bad breath he just need to breath…..
So please any suggestions??
at least some mask for time on buss and stuff as hes very emberassed and avoid talking to me cause he go mo further from me and dont speak to me on transportation as it says I don’t want people to think it’s from U + I don’t want to make U suffer…
So any suggestions???
and sorry for my english