Objective <p>To evaluate the retention of complete mandibular dentures produced via 3D-printing in comparison to those constructed from metal-reinforced acrylic resin regarding their retention.</p> Materials and methods <p>This in vivo study involved the selection of twenty patients who were completely edentulous from the outpatient clinic of the Removable Prosthodontics Department at Misr University of Science and Technology. The participants were divided into two groups, each containing an equal number of patients; the first group received complete dentures produced via 3D printing technology. For the second patient group, metal-reinforced acrylic resin was used to make mandibular dentures, while conventional maxillary dentures were constructed. The evaluation of retention was carried out for both groups.</p> Results <p>A study of various types of dentures revealed that 3D-printed dentures exhibited a statistically significant improvement in retention (<i>P</i> &lt; 0.05) relative to acrylic resin dentures that were reinforced with metal. Moreover, pairwise comparisons revealed significant increases in mean retention values at the one-month and three-month follow-up assessments.</p> Conclusion <p>The results of this clinical study led to the following conclusions: Compared to complete denture bases manufactured via conventional manufacturing techniques, those fabricated via 3D-printing offer superior fit and retention. The retention of dentures, irrespective of their type, tends to improve over time.</p>