What you have to remember is that each infection is caused by a specific bacteria, which in turn needs a specific antibiotic. Infections are identified by a testing called Gram's Staining, the result will either be Gram positive or Gram negative....if, for example, the infection you are taking Clindamycin for is a Gram negative bacteria and the abscessed tooth has a gram positive bacteria, then clindamycin may not help if it isn't designed for Gram positive bacteria. It's all kind of confusing.....so really what I'm saying is talk to your doctor or dentist about the new infection just to be sure.