The rapid advancement of digital dentistry has been significantly propelled by Digital Light Processing (DLP) 3D printing technology, renowned for its high efficiency and precision in fabricating dental restorations like crowns and bridges. However, a core challenge remains: developing resin materials that offer both excellent printability and the mechanical strength to withstand the complex stresses of the oral environment.
A recent, systematic study provides a clear solution. Focusing on a material system built around SINOMER UDMA and SINOMER PEG400DMA as the resin matrix, and SINOCURE 2425 as the photoinitiator, this research conducted a series of rigorous comparative experiments. It successfully identified the optimal material formulation and precisely defined the "golden parameters" for DLP printing.
The foundation of the study is the resin matrix itself. While UDMA is crucial for providing mechanical strength, its high viscosity can hinder printability. PEG400DMA acts as a diluent to improve flow but can compromise strength if not proportioned correctly. The first critical comparison addressed this balance.
Table 1: Effect of Different UDMA/PEG400DMA Ratios on Resin Viscosity
| Material Ratio (UDMA:PEG400DMA) | Abbreviation | Viscosity (mPa·s) |
|---|---|---|
| 8 : 2 | U8P2 | Too high, not detailed |
| 7 : 3 | U7P3 | 1253 |
| 6 : 4 | U6P4 | 701 |
| 5 : 5 | U5P5 | 407 |
| 4 : 6 | U4P6 | Further decreases |
| 3 : 7 | U3P7 | Further decreases |
| 2 : 8 | U2P8 | Further decreases |
Conclusion: The 6:4 ratio was identified as optimal, achieving the best balance between a printable viscosity (701 mPa·s) and sufficient UDMA content to maintain structural strength.
To enhance the resin's hardness and wear resistance, silanized nano-silica (SiO₂) was introduced as a filler. The key was determining the optimal loading (solid content), as it significantly affects the slurry's rheology—its behavior during spreading and layer deposition.
The study compared slurries with four different solid contents (14%, 18%, 22%, 26%) at a shear rate simulating the printing process (10 s⁻¹):
At 26% solid content, viscosity was 12.77 Pa·s, exceeding the typical DLP printing limit of 10 Pa·s, indicating poor flow.
At 22% solid content, viscosity was below 10 Pa·s, and the slurry exhibited excellent "shear-thinning" behavior (becoming thinner under shear for spreading and thicker when static to hold shape), confirming it as the optimal solid content for printability.
Thus, the finalized base slurry formula is: SINOMER UDMA and PEG400DMA at a 6:4 ratio, blended with 22% nano-SiO₂ and 1% photoinitiator SINOCURE 2425.
With the formula established, the research proceeded to optimize the printing process. The team systematically compared the impact of four key parameters on the flexural strength of printed parts, using the optimized slurry.
Table 2: Comparative Optimization of Key DLP Printing Parameters and Final Results
| Parameter | Test Range | Optimal Value | Flexural Strength (MPa) | Key Finding |
|---|---|---|---|---|
| Exposure Intensity | 14 - 29 mW/cm² | 20 mW/cm² | 132.39 ± 8.92 | Strength peaked here. Higher intensity caused internal stress and reduced strength. |
| Layer Exposure Time | 2.0 - 4.0 s | 3.0 s | 131.73 ± 9.43 | 3.0s achieved sufficient curing. Longer exposure provided no significant gain. |
| Post-Curing Time | 15 - 90 min | 30 min | 126.23 ± 8.55 | Strength stabilized after 30 minutes. Longer post-curing was unnecessary. |
| Layer Thickness | 25, 50, 100 μm | 50 μm | Best Performance | Best matched the light penetration depth (119.79 μm), yielding the strongest interlayer adhesion. |
Photocuring Property Note: Calculations determined the slurry's critical exposure energy (Ec) to be 25.54 mJ/cm² and its light penetration depth (Dp) to be 119.79 μm. The optimal exposure energy (20 mW/cm² × 3.0 s = 60 mJ/cm²) is about 2.35 times Ec, ensuring complete curing.
This research, through a series of interconnected comparative experiments, provides a complete optimization roadmap from material science to process engineering:
Material Formula: Establishes the optimal system: SINOMER UDMA/PEG400DMA (6:4) matrix, reinforced with 22% nano-SiO₂, and initiated by SINOCURE 2425.
Printing Process: Defines the precise "golden parameters" for DLP printing: Exposure Intensity: 20 mW/cm², Exposure Time: 3.0 s, Post-Curing: 30 min, Layer Thickness: 50 μm.
Under this optimized protocol, the DLP-printed dental crown and bridge resin demonstrates a flexural strength exceeding 130 MPa. This provides reliable data and a practical process blueprint for meeting the long-term mechanical demands of oral restorations. The study not only validates the excellent performance of SINOMER and SINOCURE material systems in advanced digital dentistry but also offers a feasible, high-strength, high-precision digital manufacturing solution for clinical application.
