Influence of Keratinized Tissue on Short Dental Implants: A Parallel Cohort Retrospective Study on 217 Implants with a Mean Follow-up of 4.1 Years

Purpose: To assess whether the presence or absence of keratinized tissue height (KTh) may have an influence on marginal bone levels, complications, and implant survival for short implants. Materials and Methods: The study was designed as parallel cohort retrospective research. Short implants with an implant length < 7 mm were considered. One cohort was composed of patients with short implants surrounded by ≥ 2 mm of KTh (adequate KTh); the other cohort included implants with < 2 mm of KTh (not-adequate KTh). Outcome measures were marginal bone level (MBL) changes, failures, and complications. Results: One hundred ten patients treated with 217 short and extrashort implants (4 to 6.6 mm long) were retrospectively included. The mean follow-up was 4.1 years after prosthetic loading (range: 1 to 8 years). The differences between KTh groups in MBL were not statistically significant at every follow-up considered: 0.05 mm at 1 year (P =.48), 0.06 mm at 3 years (P =.34), 0.04 mm at 5 years (P =.64), and 0.03 at 8 years (P =.82). A total of nine complications were reported: three in the not-adequate KTh group and six in the adequate group; the difference was not statistically significant (OR: 3.03, 95% CI: 0.68 to 13.46, P =.14). Five implants failed due to peri-implantitis, two in the not-adequate KTh group and three in the adequate group, without a statistically significant difference (OR: 2.76, 95% CI: 0.42–17.99, P =.29). Conclusion: This study showed no statistically significant differences in MBL, complications, and implant failure rates between short implants with adequate or not-adequate KThs. However, given the importance of patient comfort while brushing and plaque accumulation, keratinized tissue grafts could be important in selected patients, especially for those who are severely atrophic, also taking into consideration all the limitations of this study and the medium-term follow-up. Nevertheless, longer follow-ups, larger numbers of patients, and randomized controlled clinical trials are needed before making more reliable clinical recommendations.