Objective: This study assessed the impact of margin design and fabrication technique on the marginal adaptation of printable and machinable polymer-based ceramic occlusal veneers.

Materials and Methods: Thirty-six extracted human maxillary first premolars were prepared with either a butt or chamfer margin design (n=18) and randomly subdivided to receive occlusal overlays by two fabrication techniques: 3D printed or milled (n=9). The 3D-printed group used ceramic-filled resin material (VarseoSmile Crown plus, Bego, Germany) processed with a DLP printer, while the milled group used Cerasmart (GC America Inc.) blocks and a CEREC MC XL (Dentsply, Sirona) milling machine. Marginal gaps were measured at three points along the restoration using a digital microscope, and results were analyzed with two-way ANOVA.

Results: There was a significant interaction between margin design and fabrication technique (p = 0.005). For butt margins, no significant difference in marginal gap was found between 3D-printed and milled samples (p = 0.681). Chamfer margins in the 3D-printed group showed significantly larger gaps compared to the milled group (p < 0.001). Within the 3D-printed group, chamfer margins had larger gaps than butt margins (p = 0.002), while the milled group showed no significant difference between margin designs (p = 0.365).

Conclusion: Margin design and fabrication process affect the marginal adaptation of polymer-based ceramic overlays. 3D-printed restorations have greater marginal gaps than milled ones, indicating a need for improvement in 3D-printing technology for intricate patterns like chamfer margins.