Preus HR, et al. – The target of this trial was to test the theory of no difference in the 5–year clinical result of therapy between groups of patients treated with conventional over–weeks scaling and root planing or same–day full–mouth–disinfection, with or without adjunctive metronidazole. While single–level analyses demonstrated statistically significant differences, they couldn't be affirmed with more appropriate analyses and were too small to suggest metronidazole, with its risk of patient side effects and environmental consequences, for the treatment of patients with severe periodontitis.