An inadequate amount of peri-implant soft tissue results in more plaque accumulation around the implants, peri-implant mucositis, marginal bone loss, mucosal recession, and/or attachment loss. In the literature, there are studies evaluating the application of injectable platelet-rich fibrin to the gingiva and oral mucosa around teeth, but injectable platelet-rich fibrin application around implants has not been encountered. This study aimed to evaluate the effect of subgingival and submucosal application of injectable platelet-rich fibrin on peri-implant soft tissue phenotype in patients with inadequate peri-implant soft tissue phenotype.The study will include 80 systemically healthy and non-smoking patients/implants older than 18 years of age with insufficient peri-implant keratinized mucosa width and mucosal thickness who applied to Kütahya University of Health Sciences, Faculty of Dentistry, Department of Periodontology. There are two study groups according to peri-implant mucosa phenotype: Thin phenotype and thick phenotype. All patients will undergo the same procedure of injectable platelet-rich fibrin application