Open Access

Ausra Ramanauskaite, Frank Schwarz, Robert Sader

• Aim: To evaluate the influence of the width of keratinized tissue (KT) on the prevalence of peri-implant diseases, and soft- and hard-tissue stability. Materials and methods: Clinical studies reporting on the prevalence of peri-implant diseases (primary outcome), plaque index (PI), modified plaque index (mPI), bleeding index (mBI), bleeding on probing (BOP), probing pocket depths (PD), mucosal recession (MR), and marginal bone loss (MBL) and/or patient-reported outcomes (PROMs; secondary outcomes) were searched. The weighted mean differences (WMD) were estimated for the assessed clinical and radiographic parameters by employing a random-effect model that considered different KT widths (i.e., <2 and ≥2 mm). Results: Twenty-two articles describing 21 studies (15 cross-sectional, five longitudinal comparative studies, and one case series with pre–post design) with an overall high to low risk of bias were included. Peri-implant mucositis and peri-implantitis affected 20.8% to 42% and at 10.5% to 44% of the implants with reduced or absent KT (i.e., <2 mm or 0 mm). The corresponding values at the implant sites with KT width of ≥2 mm or >0 mm were 20.5% to 53% and 5.1% to 8%, respectively. Significant differences between implants with KT < 2 mm and those with KT ≥ 2 mm were revealed for WMD for BOP, mPI, PI, MBL, and MR all favoring implants with KT ≥ 2 mm. Conclusion: Reduced KT width is associated with an increased prevalence of peri-implantitis, plaque accumulation, soft-tissue inflammation, mucosal recession, marginal bone loss, and greater patient discomfort.