My mother’s two most recent cats both got gum disease and the resulting kidney disease and tooth loss. They were always fed on the ‘very best’ commercial ‘cat foods’. Her first cat, fed by my grandparents who did not believe in the new ‘pet food’ fad, lived to be 22 and never had to see a vet for any problems. She had all her teeth when she died. She was fed on table and butcher scraps, including cooked bones (now known to be risky - raw is better).
I would say drop the prescription diets for any cats with these problems. The vets are selling you the only product they can: highly processed food low in phosphorous and protein (to give the kidney less work to do). What they’re not telling you is that cats must have protein in order for their organs to function - including the kidney. That’s like telling a city dweller with asthma to breathe less, when what he should be doing is moving to the mountains where the air is cleaner and oxygen is more abundant. The key is to feed high quality protein, which is essential for the animal’s health and very, very easily processed by the kidney.
The protein in processed ‘pet foods’ is very low quality, and only 40 percent bioavailable (the cat will only get 40 percent of what is shown on the label, which in renal ‘prescription diets’ is already dangerously below the required levels). The protein in eggs, raw or cooked, is 100 percent available - and eggs are an excellent (almost perfect) food for our pets (take out the white if feding daily). In raw meat, the protein is 95 percent available. Cottage cheese is also excellent. But make sure there are bones present, as in a chicken leg (great daily meal for a cat). The cat will not eat all the bone, but will work the teeth and gums hard to get the meat off.
Please, don’t be sold on processed foods as the cure for an ailing pet and certainly not as the basis of a healthy diet. Our renal failure animals were given months to live but all but one thrived on to live to a normal living age, and they were fed primarily raw meaty bones (much more meat than bones for these guys, because of the phosphorous in bones) with some supplements to aid kidney function.
One of our adopted poodles had severe kidney and liver disease; her owner completely saw the sense of feeding the right diet, which she did brilliantly, and the vets are all amazed at the dog’s unexpected progress - they are baffled, but we just shared a knowing smile (I do educate my vets about this, and they do start to listen when they see such results). Check out the newsletter archives at http://www.b-naturals.com for more info on diets and supplements for renal disease. You’ll be blown away by the sense of it all. 
Very best of luck with your cats.
