Outcomes and Prognostic Factors of Absorbable Collagen Sponge-Assisted Apical Microsurgery: A Retrospective Cohort Study

<title>Abstract</title> <p> <bold>Aims</bold> Absorbable collagen sponge (ACS) is increasingly used as a bone void filler in apical microsurgery (AMS). However, studies on the outcomes and prognostic factors of ACS-assisted AMS remain limited. This retrospective study aimed to evaluate the outcomes and prognostic factors of ACS-assisted AMS using a time-to-event analysis and to identify prognostic factors associated with the time to success. <bold>Methods</bold> This retrospective cohort study included 91 teeth with 84 periapical lesions from 70 patients who underwent ACS-assisted AMS between January 2022 and December 2025, with a minimum follow-up of 6 months. All included patients had pre-operative and post-operative CBCT (follow-up: 6–42 months). The endpoint event was strict success, defined as CBCT-PAI ≤ 2 with no clinical symptoms. Time-to-event analysis was performed using the Kaplan-Meier method and Cox proportional hazards regression. <bold>Results</bold> Under the lenient criteria, the overall success rate was 96.4% (81/84). Under the strict criteria, the success rate was 66.7% (56/84). Lesion size ≤ 5 mm and anterior tooth location showed a significant association with success rate. In the time-to-event analysis, the cumulative probability of success was 87.1% at 36 months, with a median time to success of 17.0 months (95% CI: 13.5–20.5). In Cox univariate analyses, anterior tooth location, preoperative absence of symptoms, and lesion size≤5mm were associated with shorter time to success (P &lt; 0.05), but only lesion size remained an independent prognostic factor of time to success in the multivariable Cox regression (HR: 4.91, 95% CI: 2.49–9.67, P &lt; 0.001). The media time to success was 8.0 months (95% CI: 4.1–11.9) for lesion size≤5mm, compared with 19.0 months (95% CI: 15.5–22.4) for lesions &gt; 5 mm. <bold>Conclusion</bold> ACS-assisted AMS achieved favorable outcomes, with a median time to success of 17.0 months. Anterior tooth and lesion size were associated with success rate. Lesion size were identified as an independent prognostic factor of time to success. <bold>Clinical Relevance</bold> This study demonstrates that ACS-assisted AMS achieves predictable healing, with a median time to success of 17.0 months. Lesion size≤5 mm predicts faster healing and a higher success rate, while anterior teeth also show a higher success rate. ACS represents a alternative material for periapical bone defect management. </p>