Clinical measurement and microbiological analysis was taken at baseline, 1 month, 3 month post-treatment. Clinical parameters used in this study was probing depth, gingival recession, gingival index, bleeding on probing, plaque index, tooth mobility(Periotest Value). Microbiological analysis consisted of determination of the percentages of 4 bacterial groups according to morphologic type with phase-contrast microscope and measuring Black-pigmented Bacteroides after anaerobic culture.

1. There were significant changes in probing depth and gingival recession at 1 month(P>0.05), and these changes remained through 3 month. However, no significant differences were observed between two groups(P>0.05).

2. There were also significant reductions in gingival index and bleeding on probing at 1 month(P<0.05), and these reduced levels were maintained through 3 month with no significant differences between two groups(P>0.05).

3. In both groups, motile bacteria decreased significantly at 1 months(P<0.09), but increased nearly to baseline level at 3 month.

4. The percentages of Black-pigmented Bacteroides, in both groups, decreased significantly at 1 month(P<0.05), and in the subgingival curettage group, significant more reductions were observed than in the root planing group(P<0.05). At 3 month, significant reduction was found in subgingival curettage group only(P<0.09).

According to these results, we surmised that concomitant subgingival curettage and root planing give some advantageous effect on bacterial recolonization.