Zhao D, et al. - Authors evaluated the current evidence on the directional and non-directional associations of periodontitis with chronic kidney disease (CKD). They performed an electronic search for observational studies on the association of periodontitis with CKD in MEDLINE, EMBASE, PubMed, Open GREY and Cochrane library up to June 5, 2017. The significance of these results was limited by the high heterogeneity of studies. Findings suggested a substantial evidence on the non-directional relationship of periodontitis with CKD, while on the directional association, there are limited studies.