Clinical benefits of oral irrigation for periodontitis are related to reduction of pro-inflammatory cytokine levels and plaque

Background: Although a growing body of evidence indicates that oral irrigat ion with water has therapeutic benefits in periodontitis, the mechanisms of action have not been elucidated. The aims of this study were: (1) to analy ze the effects of oral irrigation (Water Pik(R) Oral Irrigator) on the clin ical signs of adult periodontitis (AP) and on the levels of interleukin-1 b eta (IL-beta), prostaglandin-E2 (PGE(2)), interleukin-10 (IL-10) and interf eron-gamma (IFN-gamma) in GCF, and (2) to analyze the influence of the peri odontitis-related IL-I genotype (IL-1GT) on these variables. Method: A single-center, blinded study in otherwise healthy humans (n = 52) with localized mild to moderate AP was carried out, using the following gr oups: group A (n = 12), no oral hygiene for 14 days; group B (n = 20), rout ine oral hygiene (ROH) for 14 days; group C (n=20), supra-gingival oral irr igation plus ROH for 14 days. Group A patients were crossed-over to group C for 14 days (= day 28) after a professional prophylaxis. Group assignment was randomized by a coin toss, with the exception of group A subjects, who were self-selected as per recommendations of the internal review board for human subjects. GCF was sampled from 3 study teeth per patient and analyzed for IL-1 beta, PGE(2), IL-10 and IFN gamma by ELISA on days 0, 7, 14 and 2 8. Probing pocket depths (PPD), clinical attachment levels (CAL), bleeding on probing (BOP), gingival index (GI) and plaque index (PI) were measured b y a calibrated examiner (TWS) on days 0, 14 and 28. Analysis of covariance was performed using SAS 6.12 and Proc Mixed with group and IL-1GT as the fa ctors and the baseline levels as the covariate, with output being least squ ares means and least significant difference (LSD). Significant differences were declared if the p-value for the F-statistic was less than or equal to 0.05. Results: Oral irrigation plus ROH resulted in a significant reduction in PP D, BOP, GI and PI, as well as IL-beta levels by 7 days and PGE(2) levels by 14 days, relative to ROH or no oral hygiene. Interestingly, decreased IL-1 beta levels in patients using oral irrigation plus ROH was accompanied by a trend for increased levels of the "anti-inflammatory" cytokine IL-10. ROH reduced GI, BOP and PI, and PGE(2) levels by 14 days, but had no effect on IL-1 beta or IL-10 levels relative to no oral hygiene. The effects of no o ral hygiene were reversed by a prophy followed by oral irrigation plus ROH for 14 days. No clinical differences were evident between IL-1 GT (+) patie nts (n = 11) and GT (-) patients (n = 40), but the former had significantly elevated levels of GCF IL-10 and borderline increases in IL-1 beta (p = 0. 07). Conclusions: Oral irrigation with water for 14 days had an improved therape utic benefit for AP over that of routine oral hygiene alone and this improv ement was accompanied y a down-modulation of the pro-inflammatory cytokine profile in GCF.