Something like this has good tasting doggie toothpaste and also a toothbrush AND a finger brush for you to have better control:

C.E.T. Oral Hygiene Kit: Pet Toothbrush & Toothpaste - 1800PetMeds

I would think some place like Petco or Petsmart might have the same thing or something very similar if you can't find this exact item (altho your vet prolly sells it).

I know CET also makes dental chews to prevent plague buildup.

And btw, it's more about what the dog's gums look like than the teeth themselves. Of course, plague usually causes gums to be inflamed (and then there is a definite need to get the teeth cleaned as you are trying to do), but just wanted to mention that.