Influence of Implant Positioning on Peri-Implant Colonization by Porphyromonas gingivalis and Fusobacterium nucleatum: A Prospective Longitudinal Observational Cohort Study

Introduction: Peri-implant microbial colonization plays a critical role in the maintenance of peri-implant tissue health and the development of peri-implant diseases. Implant positioning relative to crestal bone may influence the peri-implant microenvironment and affect the accumulation of pathogenic microorganisms. However, limited evidence is available regarding the relationship between implant placement depth and the prevalence of key periodontal pathogens. The present study aimed to evaluate and compare the prevalence and quantitative levels of Porphyromonas gingivalis and Fusobacterium nucleatum in the peri-implant region of subcrestal and supracrestal dental implants, and to assess their association with peri-implant clinical parameters. Materials and methods: This prospective longitudinal observational cohort study included 40 participants with functional dental implants, including 20 subcrestal and 20 supracrestal implants. Peri-implant clinical parameters, including probing pocket depth (PPD), bleeding on probing (BOP), plaque index, and radiographic bone loss, were recorded. Peri-implant crevicular fluid samples were collected from sterile paper points and subjected to genomic DNA extraction. Quantitative real-time polymerase chain reaction (qPCR) was performed to detect and quantify P. gingivalis and F. nucleatum. Detection rates, bacterial loads, and correlations with clinical parameters were analyzed at a significance level of p < 0.05. Results: Baseline demographic and clinical characteristics were comparable between the subcrestal and supracrestal implant groups, with no significant differences in age, sex, smoking status, implant location, PPD, BOP, plaque index, or radiographic bone loss (all p > 0.05). At 12 months, P. gingivalis was detected in 10 (50.0%) of supracrestal implants compared with 5 (25.0%) of subcrestal implants (p = 0.102), while F. nucleatum was detected in 13 (65.0%) and 7 (35.0%) of implants, respectively (p = 0.058). Quantitative analysis demonstrated significantly higher bacterial loads in supracrestal implants for both P. gingivalis (1.95 ± 0.86 vs. 1.52 ± 0.79 log₁₀ copies; p = 0.042) and F. nucleatum (2.32 ± 0.91 vs. 1.89 ± 0.84 log₁₀ copies; p = 0.031). In the supracrestal group, bacterial loads showed stronger positive correlations with peri-implant clinical parameters, with the strongest association observed between F. nucleatum and PPD (r = 0.61, p = 0.005), followed by BOP (r = 0.58, p = 0.007) and radiographic bone loss (r = 0.55, p = 0.009). Conclusions: Supracrestal implant placement is associated with increased colonization by periodontal pathogens and stronger relationships between bacterial burden and peri-implant tissue deterioration. Subcrestal implant placement may provide a more favorable microbiological environment and contribute to improved peri-implant tissue health.