- a) previous professional root planning; b) systemic/topic antibiotic or antiinflammatory treatment, at least 6 months prior to the initiation of the study; c) immunosuppression or need for antibiotic coverage for routine dental therapy; d) systemic condition that could affect the progression of periodontal disease (diabetes); e) pregnancy or lactation; e) allergy or intolerance to metronidazole or amoxicillin; f) smokers