3D-printed material for temporary restorations: impact of print layer thickness and post-curing method on degree of conversion

Aim: The purpose of this investigation was to evaluate the impact of print layer thickness and post-curing method on the degree of conversion (DC) of a three-dimensional (3D) print material for temporary restorations. Materials and methods: 120 specimens of the resin material NextDent C&B were additively manufactured in three different print layer thicknesses (25 µm, 50 µm, and 100 µm) using a DLP printer, and post-cured by either Labolight DUO (LL), Otoflash G171 (OF), LC-3DPrint Box (PB) or PCU LED (PCU). Each subgroup contained 10 specimens. Raman spectra were measured for the liquid state of the resin (n = 10), directly after printing (Rprint) and after post-curing (Rcured). DC and ΔDC were calculated. The data were statistically analyzed using the Kolmogorov-Smirnov test, the general linear model analysis together with partial eta-squared (ηP²), Kruskal-Wallis, and Mann-Whitney U tests (P 0.05). Result: Specimens post-cured by OF showed the highest ΔDC, followed by specimens post-cured by PB, PCU, and LL (P 0.001). Post-curing by PB, PCU, and LL resulted in the same ΔDC value range (P = 0.076 to 0.209). The print layer thicknesses of 100 µm and 50 µm (P = 0.931) showed higher ΔDC than the print layer thickness of 25 µm (P 0.001). Conclusion: The choice of the post-curing method has a high impact on the DC of the tested 3D print material followed by the specific print layer thickness. Overall, specimens post-cured by OF showed the highest DC and ΔDC values. Brands Technology Duration Wavelength Manufacturer LC-3DPrint Box (PB) Ultraviolet light (UV) 30 min Range 315 to 550 nm, peaks at approximately 360 and 435 nm NextDent (Soesterberg, Netherlands) Otoflash G171 (OF) Flashlight, nitrogen atmosphere Two processes of 2000 flashes Range 300 to 700 nm, peaks at approximately 480 and 530 nm NK Optik (Baierbrunn, Germany) Labolight DUO (LL) Light-emitting diode (LED) Two processes of 3 min Range 380 to 510 nm, peaks at approximately 395 and 475 nm GC Europe (Leuven, Belgium) PCU LED (PCU) Light-emitting diode (LED), vacuum 5 min Peaks at approximately 410 nm Dreve (Unna, Germany) Keywords: degree of conversion, Raman spectroscopy, post-curing, 3D printing, additive manufacturing, print layer thickness