1) for dahlek--- Arimidex does cause dry mouth. Once this starts, then the saliva changes, and hence the pH of the mouth changes...and down the hill you go.

2) For Nide (Bob)... receding gums... reveal parts of the tooth that don't have good or any enamel, and hence decay can start more easily.
This is when the Prevident/GelKam may help. Periogard only kills germs, it does
not do anything for loss of enamel or receding gums.
If you have periodontal disease, there is a treatment --low dose doxycycline..called Periostat that may help. This reduces inflammation of the gums. But smoking..this is not good. The oxygen levels are reduced to the
gums when you smoke. It is very hard to counteract this.

3) regarding crowns... I have a couple that are going on 20 yrs now. Can that be true??... oh gosh... 20 yrs doesn't seem like it.
My dentist is very very aggressive about crown installation --and I have to
admit with my 6 crowns now---I suffer greatly when he prepares them.
He puts a "rope" material way under the gums during impressions, and makes the crown go way down there... to be protected from decay. So while it takes me several days or a week of pain/swelling after he is through with me, I have not had alot of decay.Also when the crown is installed, he grinds the interior down..so it is way below the gum line. And he fits them tightly to the other teeth (my crowns are in the back) so food cannot be trapped easily between them. And I should explain that I have very soft teeth, and fillings you wouldn't believe. But adult decay..I do not have, yet!. (we have fluorodated water now--and maybe that is another reason?).

There are alot of reasons for poor teeth with health declining.
1) poor gums--poor nutrition low Vit C status, low CoQ-10
2) poor immunity
3) poor Vit D and calcium status
4) dry mouth/saliva deterioration due to drug therapies