Abstract: The clinical significance of peri-implant keratinized tissue (KT) has long been a matter of debate. Some studies indicate that the absence of peri-implant KT is not significantly associated with plaque control, peri-implant health status, or marginal bone loss. However, an increasing number of investigations have demonstrated that KT deficiency can promote plaque accumulation, leading to bleeding on probing (BOP), increased probing depth, mucosal recession, and even marginal bone loss. The 2017 World Workshop on the Classification of Periodontal and Peri-implant Diseases and Conditions concluded that no consensus has yet been reached regarding the minimum width of KT required to maintain peri-implant health and prevent peri-implant diseases. In recent years, a growing body of implant-specific evidence has highlighted the critical role of KT in the long-term stability of peri-implant hard and soft tissues. Currently, commonly used clinical approaches for peri-implant KT augmentation include a standalone apically repositioned flap (APF), APF combined with an autologous free gingival graft (FGG), and APF combined with a xenogeneic collagen matrix (XCM). Among these, FGG is regarded as the gold standard for peri-implant KT augmentation because of its predictable outcomes; however, it requires a second surgical site and is associated with a relatively high risk of complications. Consequently, alternative substitute materials have been actively explored in an attempt to reduce patient morbidity while maintaining clinical efficacy. This article systematically reviews the key surgical steps, clinical outcomes, and indications of the main techniques used for peri-implant KT augmentation, providing both evidence-based and experience-based guidance for clinical decision-making.

Key words: Peri-implant keratinized tissue augmentation, Apically repositioned flap (APF), Autologous tissue graft, Xenogeneic collagen matrix (XCM)