Four Paws is alright.. I would prefer C.E.T.. You can get it from the vet or Cain and Able.
Brushing the teeth for dogs is pretty much the same as humans... You only take of the soft surface particles.. You still have to get the teeth cleaned by a vet. They get tartar build up just like we do, except it seems to happen to them faster..
Dogs can also have what's called Sweet Saliva.. It causes the enamel to erode faster than normal causing tooth damage and heavy tartar build up.. Dogs with this usually need there teeth professionally cleaned at least twice a year.
I don't use toothpaste for dogs, I use PetzLife Gel, which is far more effective, and you don't even need to brush (though I do). Two of my dogs will soon be 8 yrs. old, have healthy gums, and nice white teeth, yet have never had their teeth cleaned professionally. They get raw bones regularly, which helps immensely.
True dogs diet does do a lot.. Mainly in the size of the kibble.. If you feed canned food only you are dooming your dogs to have horrible teeth. If you feed dry food, then you are going to want to find the largest kibble size you can.. This forces the dog to chew, which helps keep tartar to a minimum.. Also prevents the dog from inhaling food which can lead to vomiting.