DIFFERENTIAL CLINICAL TREATMENT OUTCOME AFTER SYSTEMIC METRONIDAZOLE AND AMOXICILLIN IN PATIENTS HARBORING ACTINOBACILLUS-ACTINOMYCETEMCOMITANS AND OR PORPHYROMONAS-GINGIVALIS/

48 adult patients with untreated periodontitis harboring subgingival A ctinobacillus actinomycetemcomitans and/or Porphyromonas gingivalis as assessed by PCR were randomly assigned to receive full-mouth scaling alone (control) or scaling with systemic metronidazole plus amoxicilli n and supragingival irrigation with chlorhexidine digluconate (test). In patients harboring A. actinomycetemcomitans intraorally at baseline , the adjunctive antimicrobial therapy resulted in a significantly hig her incidence of probing attachment level (PAL) gain of 2 mm or more c ompared to scaling alone over 12 months (p<0.05). In addition, suppres sion of A. actinomycetemcomitans in subgingival plaque below detectabl e levels was associated with an increased incidence of PAL gain. In co ntrast, patients initially harboring P. gingivalis but not A. actinomy cetemcomitans in the oral cavity showed a significantly higher inciden ce of PAL loss following adjunctive antimicrobial therapy compared to scaling alone (p<0.05). When the presence of pathogens at baseline was disregarded in the analysis, adjunctive antimicrobial therapy did not significantly enhance clinical treatment outcome. The results indicat ed that adults with untreated periodontitis harboring A. actinomycetem comitans may benefit from the adjunctive antimicrobial therapy for a m inimum of 12 months, whereas, the regimen may adversely affect the cli nical treatment outcome of patients harboring P. gingivalis but not A. actinomycetemcomitans.