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The curing characteristics of photopolymer resin determine the relationship between the vat polymerization (VP) process parameters and the layer thickness, geometric accuracy, and surface quality of the 3D printed specimen. Dispersing filler material into the photopolymer resin changes its curing characteristics because the filler scatters and absorbs light, which modifies the curing reaction. However, the ability to cure photopolymer resin with high filler volume fraction is important to 3D print material specimens for specific engineering applications, e.g. structural polymer composite materials, electrical and thermal conductive materials, and ceramic materials for biological and high-temperature environments. We methodically measure the curing characteristics of diacrylate/epoxy photopolymer resin with dispersed glass microspheres. The experiments show that the curing depth, degree-of-cure, and surface roughness depend on both the light exposure dose and the filler fraction. We determine that the degree-of-cure increases with increasing filler fraction for constant exposure dose, and approaches 90% with increasing exposure dose, independent of the filler fraction. The geometric accuracy of the 3D printed specimens decreases with increasing exposure dose and with increasing filler volume fraction due to so-called profile broadening. Finally, we show that the average surface roughness of the 3D printed specimens decreases with increasing exposure dose and filler fraction. This work has implications for VP of photopolymer resins with high filler fraction.

Objectives The aim of this study is to investigate depth dependent changes of polymerization process and kinetics of visible light-curing (VLC) dental composites in real-time. The measured quantity - "ion viscosity" determined by dielectric analysis (DEA) - provides the depth dependent reaction rate which is correlated to the light intensity available in the corresponding depths derived from light transmission measurements. Methods The ion viscosity curves of two composites (VOCO Arabesk Top and Grandio) were determined during irradiation of 40 s with a light-curing unit (LCU) in specimen depths of 0.5/0.75/1.0/1.25/1.5/1.75 and 2.0 mm using a dielectric cure analyzer (NETZSCH DEA 231 with Mini IDEX sensors). The thickness dependent light transmission was measured by irradiation composite specimens of various thicknesses on top of a radiometer setup. Results The shape of the ion viscosity curves depends strongly on the specimen thickness above the sensor. All curves exhibit a range of linear time dependency of the ion viscosity after a certain initiation time. The determined initiation times, the slopes of the linear part of the curves, and the ion viscosities at the end of the irradiation differ significantly with depth within the specimen. The slopes of the ion viscosity curves as well as the light intensity values decrease with depth and fit to the Lambert-Beer law. The corresponding attenuation coefficients are determined for Arabesk Top OA2 to 1.39 mm-1 and 1.48 mm-1, respectively, and for Grandio OA2 with 1.17 and 1.39 mm-1, respectively. For thicknesses exceeding 1.5 mm a change in polymerization behavior is observed as the ion viscosity increases subsequent to the linear range indicating some kind of reaction acceleration. Significance The two VLC composites and different specimen thicknesses discriminate significantly in their ion viscosity evolution allowing for a precise characterization of the curing process even with respect to the polymerization mechan

Objectives The aim of this study is to investigate depth dependent changes of polymerization process and kinetics of visible light-curing (VLC) dental composites in real-time. The measured quantity - "ion viscosity" determined by dielectric analysis (DEA) - provides the depth dependent reaction rate which is correlated to the light intensity available in the corresponding depths derived from light transmission measurements. Methods The ion viscosity curves of two composites (VOCO Arabesk Top and Grandio) were determined during irradiation of 40 s with a light-curing unit (LCU) in specimen depths of 0.5/0.75/1.0/1.25/1.5/1.75 and 2.0 mm using a dielectric cure analyzer (NETZSCH DEA 231 with Mini IDEX sensors). The thickness dependent light transmission was measured by irradiation composite specimens of various thicknesses on top of a radiometer setup. Results The shape of the ion viscosity curves depends strongly on the specimen thickness above the sensor. All curves exhibit a range of linear time dependency of the ion viscosity after a certain initiation time. The determined initiation times, the slopes of the linear part of the curves, and the ion viscosities at the end of the irradiation differ significantly with depth within the specimen. The slopes of the ion viscosity curves as well as the light intensity values decrease with depth and fit to the Lambert-Beer law. The corresponding attenuation coefficients are determined for Arabesk Top OA2 to 1.39 mm-1 and 1.48 mm-1, respectively, and for Grandio OA2 with 1.17 and 1.39 mm-1, respectively. For thicknesses exceeding 1.5 mm a change in polymerization behavior is observed as the ion viscosity increases subsequent to the linear range indicating some kind of reaction acceleration. Significance The two VLC composites and different specimen thicknesses discriminate significantly in their ion viscosity evolution allowing for a precise characterization of the curing process even with respect to the polymerization mechan