Actually according to the research of Dr. Lonsdale, the "flossing" action of raw meaty bones is quite effective for the removal of biofilm - which is the soft precursor of plaque.
How intensive the buildup on the teeth is depends on many different factors, including genetic predisposition. Some dogs can eat poor quality food all their lives and still maintain nice, clean teeth, others need help even when eating a completely raw diet including plenty of bones.
Many of my clients whose dogs needed some extra help have had excellent results with the homeopathic remedy Fragaria Vesca, 6X, or even better 3C pellets. One pellet per day for up to one month until tartar is significantly reduced. As a preventative from there on out one pill, once weekly.