Hi Kay,
So sorry to hear about your cat. And yes, it most likely was the dry food that caused his problems, but you were only following the advice from the vet, so it's not your fault. You were only doing what you thought were best.
Firstly, dry food does not clean teeth. Secondly, as you've sadly experienced it can cause bladder infections. Thirdly, it contains a lot of crap fillers that cats can't digest. You're right to want to put him back on a wet food
I'd suggest you ignore your vet and start using a high quality wet food such as HiLife pouches. They have around 60% meat and no fillers. Eating this should normalise your cat's urine and make it more acidic, like it normally is. Food designed to acidify the cat's urine often goes too far the other way, and causes another urinary tract problem (calcium oxalate crystals), which puts you back at square one.
You could mix in some water in the wet food too, I use filtered water for my cat - just the brittafilter on the kettle.
Is the vet doing anything to remove the crystals that are there already?
Also, the wet food will help his teeth more than the dry food, however if you want to help him keep them clean you should give him some raw meat chunks and some raw chicken wings one-two times a week for him to chew on. This cleans the teeth the way nature intended. Make sure you don't cook the bones, they must be raw otherwise they can splinter.
Best of luck
And I suggest you find another vet, with some more knowledge about cat nutrition and less focus on how much money they can make from you!