A double-blinded , placebo-controlled , randomized clinical trial was conducted in @ severe CP patients ( @ males and @ females , @ @ years old on average from @ to @ ) receiving @ different sequences of debridement-antibiotictherapy : Group A , antibiotic usage ( metronidazole , MTZ , @ g , tid , @ d ; amoxicillin , AMX @ g , tid , @ d ) was started together with SRP ( completed by @ times in @ d ) ; Group B , antibiotic usage ( MTZ @ g , tid , @ d ; AMX @ g , tid , @ d ) was started @ d after SRP ( completed by @ times in @ d ) ; Group C , SRP alone -LSB- probing depth ( PD ) , bleeding index ( BI ) and tooth mobility -RSB- was examined .