Dental treatments with implants are now being widely performed due to advances in the development of surgical procedures for dental implants and prosthodontics. However, the incidence of peri-implant diseases has been increasing with implant placement [1], and thus, the early detection of these diseases is important for maintaining dental implants. Peri-implant diseases with inflammation and the destruction of peri-implant tissues have mainly been classified into peri-implantitis with the resorption of alveolar bone around osseointegrated dental implants and peri-implant mucositis without pathological bone resorption [2]. Peri-implant diseases are diagnosed by clinical indicators including probing depth (PD), bleeding on probing (BOP), suppuration, the mobility of an implant, and radiographic bone loss (BL) [3, 4]. Clinical indicators for a diagnosis of peri-implant diseases are similar to the diagnostic indicators for periodontal diseases of natural teeth. However, the measurement of PD using a dental probe is more difficult around dental implants than around natural teeth because peri-implant tissues have less attached gingiva compared with periodontal tissue, and implant structures and prosthetic superstructures sometimes prevent a probing [3, 5]. BL of 2–3 mm on radiographs has been used as a diagnostic standard in cumulative interceptive supportive therapy (CIST) [6]; however, difficulties are associated with obtaining accurate information on slight BL on radiographs in conventional X-ray examinations. The prevalence of peri-implant mucositis and peri-implantitis was previously reported to be between 19 and 65% and between 1 and 47%, respectively [1, 7], and showed a wide range because case definition of peri-implant diseases was different among those studies in which peri-implant diseases were diagnosed using clinical indicators. These reports suggest that the case definition with the diagnosis of peri-implant diseases using clinical indicators is not sufficiently accurate or clear to evaluate pathological conditions.

The diagnosis of peri-implant diseases using biomarkers in peri-implant crevicular fluid (PICF) has recently been examined and may be more accurate than that of clinical indicators to evaluate inflammation and the degradation of tissue surrounding dental implants [4, 7, 8]. PICF contains similar components to gingival crevicular fluid (GCF), namely pro-inflammatory cytokines such as interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α), enzymes including aspartate aminotransferase (AST) and collagenase-2 (matrix metalloproteinase-8 (MMP-8)), and bone-related proteins such as cross-linked C-telopeptide of type I collagen (ICTP) and receptor activator of nuclear factor-κB (NF-κB) ligand (RANKL) [9,10,11,12,13]. These factors and proteins in PICF and GCF are regarded as diagnostic biomarkers for peri-implant diseases as well as periodontal diseases.