I guess I am lucky, never any bad experiences.......and I've had 3 senior cats with varying stages of CRF who have had dentals and never any problems.
My VERY old cat BeeJoo was a sickly stray I had found; determined to be very old but how old, who could say for sure? She had horrible teeth when I found her, and had CRF, high blood pressure, a rare condition of adrenal glands, etc. It's very likely that her horrible teeth had contributed to her CRF to begin with. I felt no choice but to have dental done, and she had several extractions as well. If anything, her BUN and Creat actually improved a little following dental.
My old cat Taco had elevated Creat and BUN for many years.....first noticed in 2000 if you can believe it. He had 3 dentals in 9 years, each time having extractions. He was also diabetic for his last 2 dentals so had to be even more closely monitored. He came out like a trooper and no noticable impact to kidneys. I was able to get his blood sugars back on track shortly after dentals.
My oldest cat Tigger (passed away in Dec of 2009), she'd had a dental back in August which included 3 extractions. This was her first dental ever - because she'd always had great teeth and gums; every year when I'd take her in for check-up, they remark how great her teeth and gums were.........and her breath was so fresh (not the usual funk breath that older cats often get with gingivitis). It was only this past summer she started to get a lot of tartar on back molars and breath started to get funky. She did pretty well after the dental though there was a period there that she didnt' want to eat much but in her case I attributed this to the suture where one tooth extracted, it came open and food would get stuck in the hole. Took me a few days to figure this out. When I did, I took her back so they could flush the piece of food out, I had them start her on antibiotics. The moment I got home after they flushed out food (the tip-off was her breath was so funky, like rotting food, which wasn't normal to me)......she ate like a pig, obviously felt so much better.
So I had 3 higher risk senior cats with known CRF and never had any bad experiences with dentals. I use a clinic that monitors BP and heart rate while under anesthetic (this is critical; not all do, and that's crazy stupid; as blood pressure can drop during anesthetic and if BP not being monitored, they're not going to know until heartrate really starts to go up...by then there's been less perfusion to kidneys, other things...so critical to find a clinic that does this.......and most where I live do NOT). I only allow the use of Isoflurane gas for anesthetic which I think nowadays, thankfully, is the normal. Much less tough on kidneys.
I also don't gork my cats up on pain killers once at home recovering. They generally give them a shot of Metacam post-op and send me home with the liquid to give, which I do not as a rule though I did with Taco for 2 days post-op because at the time I didn't know any better........and truth be told, despite his CRF, it had no ill effects whatsoever. None.
2 of my other cats, non CRF, have had dentals..........one had extractions, the other didn't need them. No problems afterward, none whatsoever.
Untreated gingivitis and bad teeth can lead to CRF and heart issues......the bacteria in gums travels through bloodstream to organs.
There was even a point where Taco had a dental 4 yrs ago and they did bloodwork pre-dental and called me to tell me his Creat was quite high, wanted to know if I wanted to proceed (i think it was 4). He very much needed the dental so I decided that to forego it would be even harder on his kidneys so they proceeded under my direction............and that was 4 yrs ago, no ill effects from same.
Something I've learned and am a huge proponent of, if cat having a dental.
Insist on the following:
1. pre-anesthetic bloodwork. this is a must. stupidly, many clinics seem to offer this as an option to owners, I guess to cut costs. Get it done. #1 so that you know where things stand prior, in case cat has funky things going on that would make anesthetic a risk..and #2, so that you have a baseline in the event that cat has problems following dental; at least then if subsequent bloodwork is done, you have something to compare to.
2. Insist on IV prior to dental. Again here many clinics seem to offer this as an option to owners, again to cut costs. This is ludicrous to me. As a human nurse who's worked with humans going for all kinds of surgery, it would be unheard of for any human to undergo any kind of surgery, even day surgery, without having an IV in place..........not only for fluids (to help prevent or counteract possible drop in blood pressure during anesthetic), but to have an effective and establish "port", if you will, so that if the patient (cat or human) "goes flat" during anesthetic, they have IV in place to give required meds........ it is unthinkable to me, to have a cat potentially "go flat" during anesthetic and have no IV in place, then try to scramble to start one which may not even be possible.
3. Insist on proper monitoring of vitals signs during anesthetic. I will not use a clinic that doesn't have proper blood pressure monitoring during this. Many clinics here don't, they just monitor heart rate. To me that's not enough. If a cat's BP drops during anesthetic and BP isn't being monitored, by the time the heart rate monitor starts to beep to signify trouble, the BP is already damn low........best for them to see the BP dropping before it becomes a critical situation, IMO.
4. If cat has extensive extractions, request post-op antibiotics. yes, they'll often give IV or IM shot of Baytril or something before discharging cat home.........but to me, a one-time dose is not enough. In my older cats who've had extractions, particularly one who had diabetes and the last thing we needed was an injection going on due to the extraction and monkeying around in there, I would insist on a week or 10 days of antibiotics. My preference was Convenia; the injectable antibiotic that is sustained release and works for 14 days. Now I've read that some cats have side effects with this; mine never did (3 of them). In one of my cats, Taco, he couldn't tolerate ANY oral antibiotic so he was the first cat to get this, we had no choice.
ALSO; to add............this is only MY preference........but in a cat with really bad gingivitis/funky mouth, I prefer a week to 10 days of antibiotic treatment PRIOR to the dental..........like Clindamycin (Antirobe). No different to me than with humans who have a bad tooth, say an abscess, and the dentist/dental surgeon will want them on a course of antibiotics prior to the dental. It's riskier to be poking around in there, doing an extraction, when there's infection in there............plus, whether humans or cats, they often do a 'nerve block' in addition to anesthetic............if tooth is bad. A nerve block doesn't take as well if infection present...........so antibiotics a good thing.
Just my 2 Canadian cents, based on my experiences.
Hope this helps.
Thanks especially to The Food Lady for that informative post! 
I want the issue solved before the dental, but then again I don't want to delay the dental for months while we try to fix his digestive issues. Will the loose stools add an additional risk to the dental procedure?
He's a farm vet - old country style.
Also, remember that if there is dental disease, not having a dental done is a risk too. Bad teeth allow bacteria into the bloodstream where they can affect the organs, especially the heart, kidneys and liver. You are making a choice either way. I prefer to have the procedure done when I know my cat is relatively healthy and stable--that way I avoid waiting until there is an infection present and my cat is at greater risk. My vet only uses isoflurane and propofol on my older kitties--that combination is safer and works well for them (the same combination was used when my kitty Willow had a feeding tube inserted prior to her passing--she was very ill at the time but came through the procedure without any ill effects).
