Colloidal silver!

Colloidal silver.  Put it in your cat's drinking water and it will help kill off infection in the teeth and gums. Not only that, even at 23 you may notice increased vitality.

If you can, try to massage and/or brush the silver into the cats teeth and gums.  If not, just put it in the water.

Here is an article that might be helpful regarding brushing/massaging the teeth:

http://www.drsfostersmith.com/pic/article.cfm?aid=56

Also, if you consider any other items first check to make sure they are safe for cats.  Some items you might consider for humans or even dogs are toxic to cats.  For example, tea tree oil, aloe vera and garlic are all toxic for cats.  Oil of oregano might be a possibility, though it will likely sting and that might not go over too well with a cantankerous cat.

All the best,

DQ