Hi Deb!
With the right diet, the right insulin, and dose adjustments via home testing, 80+% of newly diagnosed cats go into remission. However, the remission rate is only that high if all of these steps are followed. It is very hard to regulate a cat if any or all of these pieces are missing.
So first, the right diet. You'll want to ditch the dry food completely. Even the prescription dry food is still too high in carbs for a diabetic cat. The canned Purina DM is ok to feed (in fact, it's the only prescription food that is low enough in carbs for a diabetic). However, any commercial food that's low in carbs is good to feed. The quality of ingredients in the DM is not that great, about the same as Friskies. And since there are low carb flavors of Friskies, there's no point wasting money on the DM. There are many better quality foods for less than the DM. Low carb, grain free Fancy Feast is a very popular food for diabetic cats:
http://felinediabetes.com/glutenfree.htm. Here is a link to food charts that tell you the carb content of different foods:
http://felinediabetes.com/diabetic-cat-diets.htm. You can feed Merlin anything under 10% carbs (but preferably below 8%, since many cats need a little bit lower than that).
Second, is choosing the right insulin. You want to have a slow acting insulin like Lantus, Levemir, or Prozinc. Lantus and Levemir seem to work a little better than Prozinc in my opinion, but Prozinc is still a good choice and many cats do achieve remission on it. If your vet has prescribed an insulin other than these three, you will want to return it and get a new prescription.
Finally, dose adjustments via home testing. Home testing is the only way to safely and adequately make dose adjustments in your cat, just like a human diabetic would. Once we find out what insulin you're using, we can give you information about how the dose for that type of insulin should be adjusted. You can give it to your vet if they don't already have it, and work from it yourself (unless your vet is on call 24/hrs a day, you will need to make some adjustments yourself, which is why home testing is vital). I do want to warn you many vets (both bad and good) do not give good dosing advice; it's just very hard for them to keep current with every disease for every animal. Starting doses of insulin for cats should be 1 unit, according to the AAHA guidelines. Many vets often start cats out on too high a dose, and this can be both dangerous and counterproductive.
There are very, very experienced and knowledgeable people here that have helped bring hundreds of cats into remission with these treatment steps, including my own. Like with people, Diabetes is very manageable with the right treatment. Bandit's diabetes is probably one of the best things that ever happened to him--it forced me to make diet changes (getting rid of the dry food) that have made him a much healthier cat. He is the picture of health now, no longer needing insulin and eating a healthy diet. You'll see that this can really be a blessing in disguise.
One thing I wanted to point out, because you mentioned your cat's teeth and I don't want you to have any hesitation to get rid of the dry food for Merlin or even both of your cats, is that dry diets have no correlation with dental health. Both of my cats ate a dry diet most of their life, and they both developed major dental problems on the dry diet. Bandit has two teeth left in is mouth because they all had to be pulled, and the problem arose before his diet change to canned food. My Maine Coon, Gabby, ate a dry diet for 14 of her 16 years, and she had lost or had pulled all but one of her teeth, and all that happened on a dry diet. Dental health has alot to do with genetics, and whether the cat has regular dental cleanings. If you never went to the dentist to have your teeth cleaned, but you ate crunchy food all the time, would it prevent gum disease? It's the same thing with cats. Here is a great link about the subject:
http://www.catinfo.org/#Dental_Disease.
Dr. Lisa Pierson's cat nutrition web site is a wonderful resource and explains why dry food can cause so many nutrition related diseases, including diabetes:
http://www.catinfo.org
I hope I'm not overwhelming you with all of this information. There's so much to learn in the beginning, but it gets easy pretty quickly with the right steps in place. Ask lots of questions and remember to breathe! Youv'e already taken the best step you possibly could for Merlin, which is educating yourself about diabetes. This is wonderful and Merlin is a very lucky kitty.
