Photodegradation versus network densification in UV-cured PolyJet 3D-printed polymers: A structure-mechanics study

PolyJet™ 3D printing of MED610™ photopolymer is increasingly used for dental and prosthetic structures; however, the coupled effects of in-plane printing direction and post-curing temperature on network evolution, photooxidation, and mechanical durability remain insufficiently understood. Herein, MED610 specimens were printed in two horizontal orientations (X and Y) and post-cured at room temperature or 64 °C to establish a chemistry-based structure-property relationship. The Y-oriented specimens exhibited lower roughness and pore-like defects than the X-oriented specimens, leading to improved tensile and flexural performance. The room-temperature post-curing enhanced interlayer bonding and increased flexural stress by approximately 8.5% compared with the untreated Y-oriented sample, while maintaining tensile strength. In contrast, UV post-curing at 64 °C caused substantial deterioration, reducing tensile stress, flexural stress, flexural modulus, wear resistance, and effective network integrity. FTIR and XPS confirmed post-curing-induced surface chemical changes, with the O 1 s/C 1s atomic ratio increasing from 0.13 to 0.21 after 64 °C treatment, indicating enhanced surface oxidation. DMA further revealed that room-temperature post-curing increased Tg and effective crosslink density, whereas 64 °C treatment produced the lowest storage modulus and effective crosslink density. These results support a competition between beneficial network densification/interlayer strengthening at room temperature and UV-assisted photooxidative degradation within the glass-transition region at 64 °C. This work distinguishes itself from previous processing-focused studies by linking PolyJet horizontal orientation and post-curing temperature to molecular-level network evolution, surface oxidation, and wear-mechanical performance, providing guidance for optimising MED610-based dental structures within the tested conditions.