Purpose: To evaluate and compare the fit and fracture load of 3D-printed and milled composite onlays. Materials and Methods: An onlay preparation of a mandibular right molar was duplicated 28 times with 3D printing. In total, 14 onlays were milled and 14 onlays were 3D printed. The marginal and internal fit were evaluated using the silicone replica technique. For each impression, two sections were made in the silicone material. Each slice was photographed using a digital microscope, and 13 measurements were performed on both slices using ImageJ. Next, the onlays were cemented on their corresponding models and tested in a universal testing machine to determine the fracture load. Results: The printed onlays showed a significantly better marginal and internal fit (P < .05). The marginal and internal fit for the 3D-printed onlays were, respectively, 78 µm (SD 23 µm) and 222 µm (SD 30 µm), and for the milled onlays the marginal and internal fig were 100 µm (SD 38 µm) and 249 µm (SD 55 µm), respectively. In contrast, the milled onlays showed significantly better results in terms of fracture load (P < .05). Conclusions: Within the limits of this in vitro study, the printing process demonstrated a better fit but with lower mechanical properties. The fit of both the 3D printed and milled composite onlays were within clinically acceptable limits.
