Njusta, I agree that prevention is always the best route, you've been given good advice in that respect.
But if you find that despite your best efforts at prevention the plaque continues to build up, a professional cleaning may be the only option. Tooth and gum disease can lead to all sorts of problems, including serious infection.
I understand your worries about the risks of anesthesia. If professional cleaning looks like the route you have to go, we are fortunate here in Switzerland to have access to specialists in veterinary anesthesia.
Yes, most cleaning can easily be done by your general practice vet, and general practice vets are certainly qualified to do anesthesia. But when an animal is high risk for anesthesia you might consider asking your vet if it would be advisable to call in a specialist in for the operation. Perhaps having experts involved might put your mind at ease.
There is a team of mobile anesthesia specialists, led by Dr Peter Kronen, who travel to various clinics and practices in the area to assist in high risk cases.
http://www.vas-int.com/de-ch/home/
We have just gone that route with The Belltie. He has serious respiratory disease, in fact he had a life-or-death crisis last month. The little mutt managed to pull through... Only to have a tooth abscess return. We had dealt with this twice before with ABs because although this normally is a routine operation he is ultra high risk for anesthesia. But now we had to do the surgery, as the infection had spread.
Dr Isabelle Iff, a member of the VAS team, took charge of The Belltie's anesthesia... And I am happy to say that I am sitting here at Marigin watching my little Steh-Auf-Mann in the recovery box.
Info to file away in the back of your mind, just in case.
But let's hope it never comes to that, and that your prevention measures keep your cat's teeth clean and healthy.