If you ever want to see us develop a twitch when asked a question, ask us something about the teeth-cleaning ability of kibble.
First, you need to be aware that a great number of dogs don’t even (or just barely) chew their kibble. And even for the dogs who do chew their chow, there just isn’t any significant tooth-scraping that happens from eating regular kibble. (Some companies make “prescription” diets that are clinically proven to help keep dogs’ teeth clean. We wouldn’t recommend feeding any of them to a dog long-term, however. The foods are very high in fiber and fat and very low in protein, among other issues.) Expecting kibble to clean a dog’s teeth is like expecting granola to clean yours; it doesn’t work!
Tartar on a dog’s teeth forms from an accumulation of plaque; plaque forms from an accumulation of bacteria on and between the tooth surfaces, above and especially below the gums. The bacteria actually benefit from carbohydrates – typically present in higher amounts in kibble than canned food.
Sustained chewing on toys, raw meaty bones, or any safe, chewable substance can help reduce the amount of plaque on a dog’s teeth, but only brushing removes plaque reliably. Sorry!
A dog’s diet can affect the rate of accumulation of dental plaque – but it doesn’t have anything to do with the physical action of crunching the food; it has more to do with the nutritional and chemical composition of the food. Low-carbohydrate diets are associated with lower gingival and periodontal inflammation (which should be a boost for canned diets, which are almost always low in carbs). A dog’s diet can affect the pH of his saliva (at least temporarily) and the pH of a dog’s saliva can affect the rate of plaque formation – but no one has yet formulated a diet that keeps the dog’s saliva at a level that has proven to reduce plaque and tartar formation. (Oral rinses that accomplish this, in contrast, have proven to be effective at helping combat these causes of dental disease.)
Bottom line: Regular dry foods don’t keep dogs’ teeth any cleaner (free of plaque and tartar) than canned foods.