Apical bone coverage and implant survival after lateral sinus floor elevation: a retrospective study.

OBJECTIVES: This study evaluated the impact of apical bone height (ABH) on implant survival after lateral sinus floor elevation (LSFE) with simultaneous implantation, controlling for confounding factors. METHODS: A retrospective cohort of 195 implants was analyzed. ABH was measured immediately postoperatively (T1), at 6 months (T2), and at ≥ 2 years (T3), and stratified as ≤ 2 mm or > 2 mm. Survival was assessed using Kaplan-Meier curves and multivariable Cox regression, adjusting for demographic, surgical, behavior, and anatomic variables. RESULTS: ABH and endo-sinus bone gain significantly declined from T1 to T2 (p < 0.001) and continued to decrease at T3 (p < 0.001). Multivariable analysis identified ABH > 2 mm as a significant independent protective factor for implant survival at all timepoints (T1: HR = 0.100, p = 0.035; T2: HR = 0.039, p < 0.001; T3: HR = 0.040, p = 0.007). Conversely, the magnitude of ABH change did not significantly influence survival. Kaplan-Meier analysis showed markedly lower cumulative survival rates (CSRs) for ABH ≤ 2 mm (log-rank p < 0.001). At 40 months, CSRs were 20.0% at T1, 37.5% at T2, and 46.1% at T3. When ABH was excluded from the model, smoking emerged as an independent predictor (HR = 3.648, p = 0.023), while sex, age, and implant site were not significant. CONCLUSIONS: ABH decreases significantly within 6 months after LSFE and continues to decline thereafter. Critically, ABH ≤ 2 mm is a consistent and powerful predictor of implant failure, underscoring its importance in treatment planning. CLINICAL SIGNIFICANCE: Maintaining ABH > 2 mm is essential for long-term implant stability, emphasizing early monitoring and bone preservation after LSFE.