Getting a soft natural food is your best option but it does tend to be a bit pricey. Canines are supposed to get hydration from their food anyways so teeth or no it's a great idea to moisten food for them before you serve it.
Any hard food can be softened with a little water. Or canned is already soft
I agree with the people above. Wet dog food is a good option but you can make use of the dry food you currently have by moistening it with water. Basically treating the dog with no teeth like they are a puppy again. Best of luck!
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