Hi NSKN,
Glad that Tachi's eyes are alot better but sorry to hear about his other problems. Hope all goes well with the op.
Regarding the teeth, my Schui suffered really badly with gingivitis and plaque and I had to scrape his teeth daily with some stuff on a cotton bud, he also was on steroids but his was an autoimmune thing and very severe. Eventually we decided to remove the lot and he has been fine since, he is an old boy though. If I were you and could talk to my vet I would ask what she would do if it were her cat - I always do that if I am in doubt, if she has suggested it I would probably be tempted to go for it though.