BACKGROUND The present study aimed to evaluate whether non-surgical treatment interferes with clinical parameters and local patterns of osteo-immunoinflammatory mediators (IL-17 and TNF-alpha) and matrix metalloproteinase-8 (MMP-8) that are found in peri-implant crevicular fluid (PICF) and biofilms during the progression of peri-implant mucositis. MATERIAL AND METHODS We selected 30 patients with peri-implant caused mucositis before (MP) and after treatment (TP) and 30 healthy people (HP) for the analysis of IL-17, TNF-alpha cytokine, and MMP-8 production in PICF and for analysis of colonization dynamics of periodontopathogenic bacteria in supra- and subgingival plaque samples. The levels of IL-17 and MMP-8 concentrations in samples were assayed by enzymatic immunosorbent assay (ELISA) and TNF-alpha levels were determined by enzyme amplified sensitivity immunoassay (EASIA) method in PICF. The micro-IDent test was used to detect 11 species of periodontopathogenic bacteria in subgingival biofilm. RESULTS We found significantly (P<0.001) higher levels of IL-17, TNF-alpha, and MMP-8 in the PICF of the MP and TP groups in comparison to the HP group. A significant association was found in MP associated with Parvimonas micra, as TNF-alpha in PICF was significantly higher (P=0.034) than in patients without Parvimonas micra. TNF-alpha levels in the samples of PICF showed a moderate correlation with clinical parameters, including plaque index (PI) (P=0.007) and MMP-8 levels (P=0.001), in the MP group. CONCLUSIONS Assessment of levels of inflammatory cytokines in PICF can aid in the identification of peri-implant mucositis, which can assist in early diagnosis, prevention, and treatment.