Influence of print layer thickness, immersion time, and solution type on the color stainability, roughness, and...

The thickness of the print layer in 3-dimensionally (3D) printed resins may affect the clinical performance of interim crowns and occlusal devices by altering their color stainability, surface roughness, and bacterial adhesion. Studies on these effects across different resin types to optimize printing outcomes are lacking.

The purpose of this in vitro study was to evaluate the effects of printing layer thickness, immersion time, and different substances on the color stability and surface roughness of resins used for interim crowns and occlusal devices.

A total of 150 disk-shaped specimens (Ø15×1.2 mm) were printed using 2 photopolymer resins (CosmosTemp for interim crowns and CosmosSplit for occlusal devices) and 2 print layer thicknesses (25 µm and 50 µm), totaling 10 groups per resin (n=15) based on immersion solution (distilled water, tea, coffee, red wine, or soda). All specimens were postprocessed, abraded, and immersed for up to 60 days. Color changes (∆E) were measured at 0, 7, 14, 30, and 60 days using a spectrophotometer. For surface roughness and bacterial adhesion, 40 blocks (4×4×4 mm) were printed using the same parameters and divided into 4 groups (n=10) based on resin type and layer thickness. Surface roughness was analyzed with a 3D optical profilometer, and Streptococcus mutans adhesion was quantified after incubation in selective media. Statistical analysis included 3-way and 2-way ANOVA and the Kruskal-Wallis test (α=.05).

Color variation was significantly influenced by the immersion solution used, the thickness of the printing layer, and the time elapsed (P<.001). Red wine caused the greatest discoloration, particularly in specimens with a thickness of 25 µm. Surface roughness (Sa) was significantly higher for the occlusal device resin (P=.015) but was not affected by layer thickness. No significant difference in bacterial adhesion was found among the groups (P=.721).

Thinner layer thickness (25 µm) led to greater color instability over time. Red wine was the most chromogenic agent. Surface roughness and bacterial adhesion were not significantly influenced by printing resolution, although the occlusal device resin exhibited higher Sa values than the interim resin.