Depth of implant mucosal tunnel influences its microbiota: a prospective observational cross-sectional study

PURPOSE: to assess whether implant mucosal tunnel depth is associated with differences in cultivable microbial diversity in clinically healthy peri-implant tissues. METHODS: fifty-two patients with single molar implants were included after a standardized 3-month healing period and stratified into three groups according to implant mucosal tunnel depth: <3 mm, 3-5 mm, and > 5 mm. Microbial samples from the inner lining of the implant mucosal tunnel were cultured under aerobic and anaerobic conditions and identified using MALDI-TOF mass spectrometry. As a secondary exploratory outcome, TNF-α expression in peri-implant mucosa was quantified using real-time PCR. RESULTS: a total of 262 cultivable isolates representing 46 species were identified, with facultative anaerobic species predominating (81.68%). The highest Shannon diversity index was observed in the 3-5 mm group, whereas tunnels > 5 mm demonstrated reduced cultivable diversity, with clinically significant growth predominantly represented by streptococci. TNF-α expression showed a progressive increase with increasing implant mucosal tunnel depth, reaching approximately 38-fold higher levels in the > 5 mm group compared with < 3 mm (p < 0.017). CONCLUSIONS: within the limitations of this exploratory cross-sectional study, implant mucosal tunnel depth was associated with differences in cultivable microbial composition and local TNF-α expression in clinically stable peri-implant tissues. Deeper mucosal tunnels (> 5 mm) demonstrated reduced cultivable species diversity without a consistent predominance of cultivable periodontal pathogens under the applied culture conditions. The observed increase in TNF-α expression should be interpreted as a biologic association rather than evidence of active inflammation or disease. Due to the culture-based methodology and the absence of longitudinal clinical data, no conclusions regarding disease risk or progression can be drawn. TRIAL REGISTRATION: ClinicalTrials.gov, NCT05870774. Registered on 20,230,425.