I just did a little research, and radiation can cause damage to the salivary glands. it actually reduces the saliva and then somehow the saliva dries out making it thicker.
Two medications that are supposed to help are listed on the bottom and then what @A MyBCTeam Member suggested and it should improve the further out of treatment you get.

Cancer treatment
According to the American Cancer Society (ACS)Trusted Source

some cancer treatments can lead to thick saliva. These include:

chemotherapy
radiation therapy to the head or neck
These treatments can damage the glands that produce saliva. As a result, the glands can only produce reduced amounts of saliva. This saliva will dry out after, making it thicker and stickier.

These include the FDA-approved pilocarpine and cevimeline, which can stimulate salivation

Mentioned Users

A MyBCTea...

I have had intermittent dry mouth the whole time I have been on treatment. The worst is in the morning because I also happen to breathe through my mouth. I drink lots of water but what I have found that works best is ACT dry mouth lozenges. There is also a mouthwash that is prescription strength and is supposed to help but I'm not sure what it's called. I'm surprised your dentist didn't know about it.

So you are already off the hormone blocker? How long have you been off of it ?

I decided to get off the messy.no one was willing to help with all the side effects especially joint pain. My quality of life was none and they told me 7% vs being on the meds 10%. 3% was not worth it for me. I'm so over this mouth thing that I'm tempted to try hormones but I think the damage is done.

There has to be something. Did you ever take a break from the hormone drug to see ? Many of us who have had side effects have taken 'vacations'. Doctors usually ok it but then personally I make that decision. My doctor said one week but I took 4 weeks off. These drugs stay in our system for some time. As you go around here and see women who said they are taking a vacation from taken their hormone blockers maybe that is something to consider