hi, my old cat in the UK, had the calc/plaque removed twice by vets.
The first one did blood and kidney tests, then gave her a full anesthetic, did the teeth. also she stayed in overnight. Cost quite a bit. The cat had a nice smile afterwards though!

A few years later, her gums looked a little sore so I took her to a different vet. This vet said she needs her teeth needed the clean again, but this vet wrapped the car in a blanket there and then, I held her tight while the vet picked off the calc with her thumb nails and pliers! OK, the cat didn't like it, but the job was done. The vet said she the whole aneasthetic thing was overkill, especially with older cats, unless the cat needed a tooth to be removed.