I don't know that it addresses breath, but there is a very, very safe product called Healthy Mouth that you can add to their drinking water that has been clinically proven to discourage plaque from adhering to teeth (it is approved by the VOHC). It turns the water green and you want to introduce it slowly. I began using it after their last dentals at the end of last year, and in combination with brushing, their teeth still look great. Jaynie has latent kidney issues and Healthy Mouth is safe for her.
They've recently introduced gels, but I am sticking with the water additive product because it's so easy, and because I don't want to bug them too much on top of brushing.
Because Arlie had particularly poor teeth, I also used Dentatreat on her food in the evening (because I brush in the AM and didn't want to remove the benefit of the Dentatreat).