Effect of implant protrusion length on intrasinus bone formation in transalveolar sinus lift without grafting: a meta-analysis

Background: Transalveolar sinus floor elevation (TSFE) without bone grafting has gained attention as a minimally invasive approach for vertical bone augmentation in the atrophic posterior maxilla. Although implant protrusion length (IPL) is theorized to be a key determinant of intrasinus bone gain, the existing evidence is inconsistent. Objective: The purpose of this systematic review and meta-analysis is to evaluate the effect of IPL on intrasinus bone gain following transalveolar sinus floor elevation performed without bone graft materials. Methods: Electronic searches were conducted in PubMed/Medline, Scopus, Web of Science, and Science Direct until December 2024. Randomized controlled trials, cohort studies, and retrospective analyses reporting IPL and vertical bone gain (VBG) were included. Data were pooled using random-effects meta-analysis, with subgroup analyses by IPL categories (<3 mm, 3-5 mm, >5 mm). Results: = 78%). The osteotome technique demonstrated superior consistency compared to threaded expanders. Conclusion: Controlled implant protrusion (3-5 mm) optimizes bone formation in graft-free TSFE, offering a biologically driven alternative to graft-dependent approaches. Standardization of IPL measurement protocols and long-term implant survival studies are warranted to refine clinical guidelines.