To evaluate the clinical effect of peri-implant free gingival grafting (FGG) at different timing in the posterior mandible.

A total of 40 patients with keratinized gingival insufficiency (with a width of 2 to 4 mm) of a single missing tooth in the posterior mandibular area were selected from the Department of Implant Restoration, Dongguan Jianli Stomatological Hospital, from October 2018 to October 2020. The patients were randomly divided into experimental and control group. In the experimental group, the healing abutment was placed during the first-stage surgery and FGG was performed at the same time. In the control group, submerged healing was performed in the first-stage surgery, and in the second-stage surgery in 3 months, FGG was performed and the healing abutment was placed at the same time. The survival of the graft was observed after surgery. The width of the remaining keratinized gingiva on the alveolar ridge was measured before operation. The width of the buccal FGG immediately after the operation, the width of the keratinized gingiva in 2 months after transplantation, the keratinized gingiva immediately after crown delivery, and the width of the buccal keratinized gingiva 6 months after crown delivery were measured.

The operations in both groups were successful. The wounds healed normally, and the tissue flaps survived. The width of the remaining keratinized gingiva on the alveolar crest of the experimental and control group before surgery were (2.9 ± 0.3) and (3.0 ± 0.3) mm, respectively, and there was no significant difference between the two groups. The width of the keratinized gingiva measured at the midpoint of the buccal gingival margin of the experimental and control group immediately after surgery was (4.9 ± 0.5) and (4.9 ± 0.5) mm, respectively, and the difference was not statistically significant (t = 0.2, P = 0.8) . Besides, the width of the keratinized gingiva measured at the midpoint of the buccal gingival margin in 2 months after operation was (4.2 ± 0.4) and (4.5 ± 0.4) mm, respectively, and the difference was statistically significant (t = -2.9, P<0.05) . In addition, the width of the keratinized gingiva at the midpoint of the buccal gingival margin of the implant measured on the day of crown delivery was (3.2 ± 0.4) and (3.7 ± 0.5) mm, and the difference was statistically significant (t = -2.6, P<0.05) . Moreover, the width of the keratinized gingiva at the midpoint of the buccal gingival margin of the implant measured in 6 months after teeth placement was (3.1 ± 0.4) and (3.5 ± 0.3) mm, and the difference was statistically significant (t = -3.7, P<0.05) .

When the width of the residual keratinized gingiva in the posterior mandibular area is 2 to 4 mm, FGG can achieve better effects of increasing keratinized gingiva at both the first- and second-stage surgery. Compared with the first-stage surgery, FGG performed at the second-stage surgery can achieve higher width of the buccal keratinized gingiva, the drawback of more operations.