Background: The autogenous bone core block (BCB) is a viable, biologically advantageous, and minimally invasive alternative to other augmentation procedures for small bone defects around dental implants. This study focused specifically on horizontal vestibular defects in the mandible, a frequently encountered yet underrepresented clinical situation, to evaluate the effectiveness and predictability of bone core grafting. Methods: Cylindrical autogenous bone cores, harvested from the implant-site osteotomy using trephine drills with a 2.5 internal diameter, were stabilized with osteosynthesis screws, and implants were placed simultaneously. Initial preoperative measurements of the edentulous ridge width were performed based on cone beam computer tomography (CBCT). At 4 months postoperatively, a subsequent CBCT measurement was performed for each implant site. Results: A total of 38 augmentation procedures were analyzed with a mean horizontal bone gain of 1.8 mm (p = 0.000). Improved outcomes were observed in V-shaped defects with remaining vertical bony walls, which contributed to better graft stability and volume preservation. While Khoury et al. previously validated the general applicability of this technique across various defect types, our study refines its indication by offering a clear protocol tailored to a common clinical niche. Conclusions: The proposed BCB method proved to be a safe, efficient, and with reduced morbidity procedure, providing clinicians with a practical and evidence-based tool for predictable horizontal bone augmentation