28 participants in both control and test groups (14 patients in each group) receive mucogingival surgery to increase the width of attached keratinized peri-implant mucosa. They should have at least one implant lacking attached mucosa on the buccal side. Baseline measurements includes the width of keratinized gingiva in the buccal side of implants (as primary outcome), plaque index, gingival index and probing pocket depth in adjacent natural teeth. Furthermore, surface texture and color are recorded using photographs. For both groups, the recipient bed is prepared using a surgical blade (number 15), beginning from the mucogingival line, as a split thickness periosteal bed. Muscle attachments are incised to create a periosteal bed. The mucosal flap is sutured to the buccal mucosa or it is removed. For the participants in the control group, a free gingival graft is harvested from the palatal area. The graft size is determined using an aluminum foil placed on the recipient bed. The gingival graft is stabilized by 4-0 vicryl absorbable sutures. In the test group, an amniotic membrane graft is cut to the appropriate size, then, it is fixated using the similar sutures. Immediately after homeostasis, the width measurement and clinical measurements are repeated. The measurements are repeated after the 1st, 2nd, 6th and 12th weeks. The participants are asked to fill the VAS pain related questionnaire in every recall sessions.