Full mouth SRP will be initiated on Day 1 followed by randomized treatment of that side. If necessary, SRP and randomized treatment may be completed on the other side of the mouth on Day 2. Treated pockets that still have a PPD ≥ 5mm at the 4 and 12 week visits will be retreated with SRP or SRP plus placebo or PS, as randomized. Assessments will be conducted over a 24 week (6 month) period including safety assessments and assessments of dental parameters (PPD, BOP, Plaque index, Gingival Index, Clinical attachment level).