Influence of thermal-cycling or staining medium on the surface properties and color stability of conventional, milled, and 3D-printed base materials

The study of denture base resin fabricated by digital technology with surface properties or color stability remains limited. In this study, thermal cycling and staining media (distilled water, artificial saliva, green tea, and Coca-Cola) immersion were used to simulate the intraoral environment to assess the surface properties and color stability of CAD/CAM (milled) and 3D-printed base resin materials, the conventionally polymerized base served as the control group. After thermal cycling, all groups showed increased surface roughness, contact angle (i.e. hydrophilicity) and color difference (∆E), the 3D-printed group had the most significant increase among the 3 groups (P<0.001). While there were no significant difference (or the difference is very small) between the conventional and milled groups. After 7 and 30 days of immersion in four staining media, the ∆E values remained highest in the 3D-printed group (∆E ≥ 3.34) (P<0.001), exceeding the clinically acceptable threshold (∆E = 2.7) at 30 days. Additionally, all groups showed significantly higher ∆E values after 30 days compared to 7 days (P<0.05). The 3D-printed group exhibited a rougher surface, poorer hydrophilicity, and reduced color stability compared to the conventional or milled groups, indicating that further improvements are needed before clinical application.