Role of Keratinized Mucosa on the Risk of Peri-Implant Diseases and Soft Tissue Dehiscence in the Posterior Mandible-A 20-Year Prospective Cohort Study.

Aim: To evaluate the 20-year outcomes of tissue-level implants placed in the posterior mandible, comparing implants surrounded by keratinized tissue (KT) or alveolar mucosa (AM).

Methods: At baseline, 128 patients (128 implants) were rehabilitated with implant-supported fixed dental prostheses in the posterior mandible and enrolled in a supportive periodontal/peri-implant care (SPC) program. Patients were categorized based on the presence (KT) or absence (AM) of keratinized mucosa. During the first 10 years of SPC, 11 AM patients underwent free gingival grafting (FGG), identifying a third group (AM + FGG). At the 20-year follow-up, peri-implant health status and soft-tissue dehiscence were assessed according to the 2018 Case Definitions. The need for additional treatment between the 10- and 20-year examinations was also recorded.

Results: Of the 98 patients evaluated at the 10-year follow-up, 64 (KT = 42; AM = 16; AM + FGG = 6; drop-out rate: 35%) attended the 20-year examination. Additional treatment was required in 11 AM patients (50%) versus 2 KT patients (5%) (p < 0.01). AM implants exhibited significantly greater marginal bone loss, bleeding on probing, and soft tissue recession compared to KT implants (p < 0.01). The application of an FGG (AM + FGG = 6) had a protective effect on peri-implant health status at 20 years. Peri-implantitis was diagnosed in 4.2% of implants surrounded by keratinized mucosa (KT or AM + FGG) versus 25% in the AM group (OR = 6.67; 95% CI: 1.09-40.9; p = 0.041).

Conclusion: Tissue level implants placed in the posterior mandible without KT showed greater marginal bone loss, bleeding on probing, soft tissue recession, and peri-implant diseases compared to implants with KT at 20 years.