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 irrigation with water has therapeutic benefits in periodontitis, the mechanisms of action have not been elucidated. The aims of this study were: (1) to analyze the effects of oral irrigation (Water Pik(R) Oral Irrigator) on the clinical signs of adult periodontitis (AP) and on the levels of interleukin-1 beta (IL-beta), prostaglandin-E2 (PGE(2)), interleukin-10 (IL-10) and interferon-gamma (IFN-gamma) in GCF, and (2) to analyze the influence of the periodontitis-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 groups: group A (n = 12), no oral hygiene for 14 days; group B (n = 20), routine oral hygiene (ROH) for 14 days; group C (n=20), supra-gingival oral irrigation 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 28. Probing pocket depths (PPD), clinical attachment levels (CAL), bleeding on probing (BOP), gingival index (GI) and plaque index (PI) were measured by 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 factors and the baseline levels as the covariate, with output being least squares 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 PPD, 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 oral hygiene were reversed by a prophy followed by oral irrigation plus ROH for 14 days. No clinical differences were evident between IL-1 GT (+) patients (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 therapeutic benefit for AP over that of routine oral hygiene alone and this improvement was accompanied y a down-modulation of the pro-inflammatory cytokine profile in GCF.