Antirobe (clindamycin) is used to kill dental infections, among other
things. Since dental cleaning stirs up mouth bacteria, my vet gives
it for a week before cleaning the teeth if the cat has gingivitis.  
I don't believe it's a substitute for cleaning.

BarB

Antirobe is Pharamcia's (formerly Upjohn) major anaerobic
antibacterial. It is one of the very few antibiotics that are effective
against anaerobic bacteria. Anaerobic bacteria exist where oxygen is
scarce, unlike most bacteria. The oral bacteria in the gums and deep
tissues is commonly anaerobic in nature and thus Antirobe is uniquely
suited for this work. Another major plus for Antirobe is that it is
adsorbed very quickly getting effective levels in the bloodstream
within half an hour. Generally this is used prophylactically to insure
that bacteria are not dislodged during the cleaning process and end up
attching to the mitral valve of the heart where some dental bacteria
like to reside.

It's basically clindamycin - which works WITH, but not in place of, a proper
dental cleaning. At our shelter, we treat with clindamycin before and after
the actual cleaning takes place.