It's the bones that help with the cleaning- but they must be raw, not cooked.
Also the saliva they produce to digest raw food helps to break down plaque.
The Plaque Off is great stuff but you can't use it on cats that have thyroid problems or pregnant or lactating queens.
You could also try the homeopathic remedy Fragaria- given once a week helps to prevent the build up of plaque in the first place.