Marketing claims that diets "clean teeth" or "freshen breath" appeal to
consumers, but they are a bit ambiguous from a scientific point of view when
one wishes to compare diets.  References to "dental benefit", or lack
thereof, without specific mention of what that entails can be similarly
vague.  Therefore, it is important to note that the VOHC Seal is granted
only to those diets shown to reduce plaque and calculus accumulation by a
certain amount over a standardized dry diet control.  (Theoretically,
reduction of plaque and calculus accumulation should lead to reduction of
periodontitis and gingivitis, however, measurement of those conditions are
not in the VOHC protocol.)

Cats fed dry diets generally do have less plaque accumulation than those fed
wet food, however, there are currently only three feline diets with the VOHC
Seal:  Hills T/D, Friskies Dental Diet, and Science Diet Oral Care.  This
does not mean that dry diets without the Seal have no dental benefit; it
only means that they have not been shown to reduce plaque and calculus
accumulation by a certain amount over a standardized dry diet control.
Regardless, when primarily concerned about pets' teeth, it almost always
makes much more sense to follow a proper home care regimen and see a
veterinarian for regular oral health evaluations and periodontal treatments.

Edward