A new method of protecting dogs from plaque is the application of a plaque prevention gel, like OraVet. These gels must be prescribed by a veterinarian. 

OraVet Plaque Prevention Gel helps reduce the formation of plaque and tartar in a  dog's mouth. It acts as an invisible barrier and helps prevent bacteria from sticking to the surface of teeth. The gel is tasteless and odorless and is applied once, weekly. It must be stored below 86 degrees (so not in a garage or shed). 

Here's what OraVet advises about applying the gel: "Put a generous amount of gel on the applicator. While holding your dog's mouth closed, lift the upper lip on one side and spread the gel on the upper teeth and gums at the gum line. (Note that it is only necessary to apply the gel to the front of the teeth and gums.) Now spread the gel on the lower teeth and gums at the gum line. Repeat the same procedure on the other side. Discard the applicator and any leftover gel."

Contact your vet for details and whether it's recommended for your dog.