I had a kitty that had really bad teeth. What can I say, I got her when I was a poor struggling grad student then a post-doc didn't pay much either. Her teeth were a mess and she had just been diagnosed with chronic renal failure, she was about 13. They did the tests to be sure she could handle it after I spent a couple months giving her fluids to help her with the kidney failure. In the end, they did the cleaning and she felt so much better. They joked that she was the only renal failure cat they had who gained weight. That was all due to the fact that she felt so much better with her teeth cleaned (and a couple pulled). She lived 6+ more years with the renal failure, and I'm sure the cleaning helped her do so well. Though I will admit that as we went along, I declined to do another cleaning because I worried about the risk/benefit ratio with her.