Is there a need for keratinized mucosa around implants to maintain health and tissue stability?

AIM: The objective of the present review was to analyze the literature with regard to the need for keratinized mucosa around implants to maintain health and tissue stability.
METHODS: Human and animal studies were identified through electronic and hand searches. Predetermined outcome measures were (i) implant loss, (ii) peri-implant health, (iii) oral hygiene, (iv) soft-tissue recession, (v) change in marginal bone level, and (vi) patient-centered outcomes. With respect to outcome variables, change in "attachment level", soft-tissue recession and change in peri-implant bone level were only retrieved from longitudinal studies. For remaining parameters, cross-sectional studies were also considered.
RESULTS: Nineteen relevant publications were identified (17 human and 2 animal studies). Due to marked heterogeneity in study design and reported data, no statistical analysis of retrieved data was feasible. Twelve human studies reported plaque scores for sites with "adequate" (≥2 mm) and "inadequate" (<2 mm) width of keratinized mucosa, and in five studies, an "inadequate" width was associated with a significant higher plaque score. Half of the studies showed significantly higher bleeding scores at implants with < 2 mm of keratinized mucosa, while the majority of publications (8 of 10) found no differences for probing depths. Two of three longitudinal studies reporting on recessions described no long-term differences with regard to the amount of keratinized mucosa. Evidence on the effect of keratinized mucosa on bone-level changes or implant loss was scarce, and no conclusions could be drawn. No article reporting patient-centered outcomes could be identified.
CONCLUSION: Collectively, the findings of this review show that evidence in support of the need for keratinized tissues around implants to maintain health and tissue stability is limited.