RESUMO
OBJECTIVE: The aim of this randomized double-blind and placebo-controlled study was to assess if periodontal treatment with or without systemic antibiotic would change the mean level of Archaea. METHODS: Fifty-nine (59) subjects were randomly assigned to receive scaling and root planing (SRP) alone or combined with metronidazole (MTZ; 400 mg/TID) or either with MTZ and amoxicillin (AMX; 500 mg/TID) for 14 days. Clinical and microbiological examinations were performed at baseline and at 6 months post-SRP. Six subgingival plaque samples per subject were analysed for the presence and levels of Archaea using quantitative polymerase chain reaction. RESULTS: Scaling and root planing alone or combined with MTZ or MTZ + AMX significantly reduced the prevalence of subjects colonized by Archaea at 6 months post-therapy, without significant differences among groups (P > .05). Both therapies led to a statistically significant decrease in the mean percentage of sites colonized by Archaea (P < .05). The MTZ and MTZ + AMX group had a significantly lower mean number of sites colonized by Archaea and lower levels of these micro-organisms at sites with probing depth ≥5 mm at 6 months compared with SRP group (P < .05). CONCLUSION: Periodontal treatments including adjunctive MTZ or MTZ + AMX are more effective than mechanical treatment alone in reducing the levels and prevalence of sites colonized by Archaea in subjects with chronic periodontitis.