A short-term longitudinal study was carried out to assess how microbiological and clinical characteristics, measured surrounding periodontal sites with amalgam class II fillings intentionally made to overhang, vary following their replacement with a correct form of filling. The results of the study showed a significant reduction of the total bacterial count and the percentages of Gram-negative and anaerobic organisms spreading from overhanging fillings to non-overhanging fillings. The paper concludes that, as has been already demonstrated in the case of onlays, there are both qualitative and quantitative variations in the subgingival plaque in the presence of overhanging fillings which can lead to periodontal damage.