Effect of Subcrestal Placement of Platform-Switched Implants on Bone Loss: A Narrative Review of Clinical, In Vivo, and FEA Studies

Abstract

Aim: The effect of placing platform-switched (PS) implants subcrestally versus equicrestally on peri-implant bone loss remains controversial. This narrative review critically appraises the evidence from biomechanical, animal, and clinical studies to determine if an optimal implant placement depth exists. Materials and Methods: A systematic search was conducted in PubMed, Google Scholar, and Scopus for studies published since 2015, following Preferred Reporting Items for Systematic reviews and Meta-Analyses guidelines. The PICO-driven search included clinical, in vivo, and finite-element analysis (FEA) studies comparing subcrestal and equicrestal placement of PS implants. Risk of bias was assessed using randomized clinical trials (RCTs) using the Risk of Bias Tool 2.0. Results: Seventeen articles were included (nine clinical, four in vivo, and four FEA). FEA studies suggest that subcrestal placement (<2 mm) can confer biomechanical advantages, but these findings are highly dependent on idealized model parameters like cortical bone thickness. The four in vivo studies provided conflicting and inconclusive results. A quantitative summary of nine clinical studies (n = 952) revealed no significant overall difference in bone loss between subcrestal and equicrestal placement (Std. mean difference: 0.10; 95% confidence interval: -0.42 to 0.62). However, this finding is compromised by substantial and significant heterogeneity across studies (I 2 = 86.7%; P < 0.0001). Conclusion: Despite biomechanical promise in simulation models, there is currently no conclusive clinical or in vivo evidence to support routine subcrestal placement of PS implants over equicrestal placement for mitigating bone loss. The high heterogeneity in clinical data underscores an urgent need for large-scale, standardized RCTs with long-term follow-up to resolve this ongoing debate.