It's not true that kibble cleans plaque - if it were then we wouldn't find so many dogs and cats with oral health issues. The truth is that dogs rarely chew their food. If you ever seen dog vomit, you'll have seen intact grains of kibble. Even if they do chew, their sharp teeth cut into the kibble and so the kibble never really rubs against the gums, which is where dental health issues arise. Healthy teeth depend on a healthy diet and, of course, brushing.