Why is periodontal debridement (scaling and root planing) necessary before any form of antimicrobial or antibiotic is administered?

What will be an ideal response?

It is necessary to physically remove the biofilm by instrumentation, then the antimicrobial agent can be administered. For this reason, administration of antimicrobial agents should never be the sole treatment and always should be as an adjunct to periodontal debridement and/or periodontal surgery. The biofilm structure also may account for the rapid rebound or repopulation of the pathogenic flora, which occurs frequently after the use of antimicrobial agents.