Objective <p>This study assessed the clinical efficacy of the combined Apically Incised Coronally Advanced Surgical Technique (AICAST), deproteinized bovine bone mineral, and a collagen membrane for guided tissue regeneration (GTR) in intrabony defects, and compared outcomes with the papilla preservation technique.</p> Methods <p>A single-center, parallel-arm, randomized controlled trial was conducted involving 26 patients with 39 deep intrabony defects in patients with periodontitis. The test group (<i>n</i> = 23 defects) received guided tissue regeneration (GTR) using the apically incised coronally advanced surgical technique (AICAST) combined with deproteinized bovine bone mineral and a collagen membrane. The control group (<i>n</i> = 16 defects) received GTR using the papilla preservation technique (PPT) with the same bone graft and membrane. The primary outcome was the change in clinical attachment level (CAL) at 12 months postoperatively. Secondary outcomes included changes in probing depth (PD), bleeding on probing (BOP), plaque index (PI), papilla tip (TP) position, radiographic new bone height (NB), supracrestal new bone (SUPRA-NB), and supracrestal attachment gain (SUPRA-AG), as well as early postoperative outcomes (wound closure score, VAS pain score, and PI at 1 and 2 weeks). Clinical parameters and cone-beam computed tomography measurements were obtained at baseline and at 3 and 12 months postoperatively.</p> Results <p>Both groups demonstrated statistically significant improvements at 3 and 12 months postoperatively in PD, BOP, PI, and CAL. The mean CAL gain at 12 months was 3.04 ± 1.10&#xa0;mm in the test group and 2.88 ± 1.13&#xa0;mm in the control group (between‑group difference: 0.16&#xa0;mm; 95% CI: − 0.66 to 0.98; <i>p</i> = 0.702). At 1 and 2 weeks postoperatively, the test group exhibited significantly lower plaque index values compared with the control group (<i>p</i> = 0.023 and <i>p</i> = 0.020, respectively), indicating improved early postoperative plaque control. After 12 months, the papilla tip position demonstrated a statistically significant change in the test group (<i>p</i> = 0.012), whereas no significant change was observed in the control group (<i>p</i> = 0.764). Comparable outcomes were observed between groups with respect to new bone height, supracrestal bone formation, and clinical attachment gain. The mean increase in new bone height was 2.67 ± 1.66&#xa0;mm in the test group and 3.30 ± 2.11&#xa0;mm in the control group (<i>p</i> = 0.302).</p> Conclusion <p>The combined AICAST and GTR approach was associated with significant improvements in clinical parameters in the management of intrabony defects. When compared to the conventional technique, this approach was associated with improved early plaque control and enhanced papillary position at 12 months, while achieving comparable regenerative outcomes. These findings support the use of AICAST as a viable surgical option for periodontal regeneration; further studies are warranted to evaluate its broader applicability and long-term efficacy.</p>