Effect of Peri-implant Keratinized Tissue Width on Tissue Health and Stability: Systematic Review and Meta-analysis

Purpose: There is uncertainty in the literature on whether the presence of keratinized tissue (KT) ameliorates the state of peri-implant tissue health. A systematic review and meta-analysis was performed to synthesize evidence on the association between peri-implant keratinization, defined as adequate (≥ 2 mm) or inadequate (0 to 2 mm), and peri-implant health and stability, measured as tissue inflammation, plaque accumulation, tendency to bleeding, and probing depth (PD). Materials and Methods: This systematic review adhered to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) statement and was registered on PROSPERO. According to predefined inclusion criteria, full papers for potentially eligible studies resulted from electronic databases (PubMed, Cochrane, and OpenGrey) and screening of titles/abstracts. Publication bias and risk of bias in primary studies were assessed. The primary outcome was gingival inflammation, measured with Gingival Index (GI) and modified Gingival Index (mGI). Additional outcomes were plaque accumulation (mPI/PI), bleeding (bleeding on probing/modified Bleeding Index), and PD. For each outcome, a random-effects meta-analysis was performed comparing the adequate group (≥ 2 mm, KT1) and the inadequate group ( 2 mm, KT0) KT width. The mean number of implants and proportion of mandibular implants were investigated as potential causes of heterogeneity using meta-regression. Sensitivity analysis was performed excluding low-quality studies. Results: From 362 screened studies, a total of 15 papers were included in the systematic review, and 8 articles were finally included in the meta-analysis. Heterogeneity was found for all outcomes. The main analysis showed a statistically significant association between adequate KT level and a lower mGI-GI (standard mean difference [SMD] KT1 vs KT0 = -1.25, 95% CI = -2.12 to 0.37, P = .01). For plaque accumulation (SMD = -1.18, 95% CI = -2.36 to 0.00, P = .05), bleeding (SD = -1.99, 95% CI = -4.60 to 0.61, P = .13), and PD (MD = -0.06, 95% CI = -0.13 to 0.01, P = .10), no statistically significant difference was detected; however, the trend of results was in favor of the KT1 group. The sensitivity analysis supported the main analysis conclusions. Conclusion: The importance of having an adequate KT width around implants was confirmed by this review; adequate KT was significantly associated with less peri-implant inflammation evaluated qualitatively with mGI/GI. No difference was found for plaque accumulation and bleeding, but a positive trend was found favoring implants with adequate KT. Keywords: keratinized tissue, peri-implant health, systematic review