The patients were divided into two groups based upon the diagnosis of PD (maximal probing depth ≧ 4 mm) (a), three groups based upon the severity of PD (EWP) (b), or two groups based upon the presence of P. gingivalis in subgingival biofilm (c). MTX treatment introduction in each groups were compared by cumulative hazard method. X axis indicates days for MTX treatment introduction after the first visit. Y axis indicates the cumulative hazard ratio for MTX introduction. Hazard ratio of positive PD (probing depth≧4mm) vs negative PD was 2.68 (95% CI, 1.11–6.50), p = 0.03. Hazard ratio of severe PD (EWP) vs non PD (EWP) was 7.26 (95% CI, 0.75–69.9), p = 0.09, and hazard ratio of moderate PD vs non PD was 4.42 (95% CI, 0.60–32.4), p = 0.15. Hazard ratio of positive Pg vs negative Pg was 0.77 (95% CI, 0.39–1.53), p = 0.45.