I think the most important thing in terms of preventing tooth decay is a good brushing routine, regardless of type of diet.
With that being said, I like to mix! Mostly for variety and increasing water intake. Toki isn't very picky and will eat plain ol' kibble but sometimes needs encouragement getting started on breakfast. I take a small spoonful of canned food and mix it with some warm water to make a loose gravy (we are watching calories and the water really helps with fullness without the calories and also stretches the canned food) and mix in her kibble with that for breakfast.
My favorite canned foods that we use are Tiki Dog, Party Animal, and Weruva. We also use the Nature's Variety Instinct although I mix that with some canned pumpkin (suggestion I found here!) to cut down on the richness of the food. I've heard great things about Fromm's canned line and will try it eventually (they only sell it in the big cans as far as I know so it takes us a while to get through them
). I've also used like a 1/4 of a rehydrated Stella & Chewy's freeze-dried patty to mix with kibble as well. We do a lot of mixing!