Choosing what you want to feed your dog in terms of feeding kibble versus wet food carries many different considerations.
Dry food is usually what many dog owners decide to feed their dogs. Because its low concentration of water (~10%) and how easy it is to transport and serve this is usually the more economical choice. Because kibble is dry people tend to think that it'll help keep tartar build up low because it scraps the teeth. This isn't entirely wrong or right. The kibble pieces break apart at the tip of the tooth so not much scraping action goes on near the base of the teeth. Special bones and treats can be given to the dog to help with tartar build up but kibble alone won't eliminate the problem.
Semi moist foods aren't always the best choice, simply because they are high in sugar and salt and most of our pets don't need the extra salt/sugar. Sticky and sugarly foods can also contribute to certain dental diseases that are responsible for tooth loss in dogs and cats
Wet foods have high concentration of water but can be more convinient to use for small dogs. But because of smallers dog's crowded teeth the soft nature of wet food can certainly contribute to faster plaque build up in the teeth. (Although tartar will always be there no matter what diet the dog is on, this is why it is important to keep your dog's dental hygiene in tip top shape!).
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http://peteducation.com/article.cfm?c=2+1659+1661&aid=3328