Julia,
the saliva glands are hit pretty hard during radiation. If I recall correctly it was somewhere around the end of the first week where I started to notice and around the third week where I could complain about dry mouth.

Every case is extremely different due to how they radiate the field, especially considering the amount of surgery he has already had to the location.

On the flip side, I am nearly 1.5 years out and I only get dry mouth at night now. I keep a glass of water by the bed and it is pretty manageable.

Even though my saliva is present it is considerably different(much thinner and slower flow) and I hate eating without having a glass of milk to help create the right viscosity.