The effect of layer thickness, curing time, and thermal aging on the physical and mechanical properties of a 3D-printed permanent crown resin

The Effect Of Layer Thickness, Curing Time, and Thermal Aging On The Physical and Mechanical Properties Of a 3D-Printed Permanent Crown Resin Aim: Three-dimensional printing technologies provide significant advantages in the fabrication of dental materials in terms of speed, precision, and customization. This study aimed to investigate the effects of layer thickness, post-printing curing time, and thermal aging on the water sorption/solubility, surface roughness, and flexural strength of a 3D-printed permanent crown resin. Material and Method: A permanent crown resin (VarseoSmile TriniQ; BEGO GmbH & Co. KG, Bremen, Germany) was printed at a 90° build orientation using 50 and 100 µm layer thicknesses. A total of 120 disc-shaped specimens (15 mm diameter, 1.5 mm thickness; n = 60 per layer thickness) were fabricated using an Asiga MAX 2 UV printer (Asiga, Sydney, Australia). Post-processing cleaning was performed in 99% isopropyl alcohol (IPA) using a Pro-Sonic 600® ultrasonic cleaner (Sultan Healthcare, Salt Lake City, UT, USA). The specimens were randomly divided into three curing groups (n = 20) and post-cured using an Otoflash G171 unit (NK-Optik GmbH, Baierbrunn, Germany) at 2000, 4000, and 8000 flashes. Following curing, half of the specimens from each group were stored in distilled water for 24 h (Group 1), while the remaining specimens were subjected to thermal aging for 5,000 cycles between 5–55 °C (Group 2; n = 10). Surface roughness was measured using a mechanical profilometer (Taylor Hobson, Leicester, UK), and surface topography was examined by scanning electron microscopy (JSM-6610; JEOL Ltd., Tokyo, Japan). Biaxial flexural strength was evaluated using a universal testing machine (Instron 3344, Metalinspec, Canton, USA). Statistical analyses were performed using SPSS software (SPSS Inc., Chicago, IL, USA). Independent sample t-tests or Mann–Whitney U tests were applied for two-group comparisons, while ANOVA or Kruskal–Wallis tests were used for multiple-group comparisons. The level of significance was set at α = 0.05. Results: No statistically significant effects of layer thickness or curing time were observed on water sorption and solubility (p > 0.05). Regarding surface roughness, specimens cured with 4000 flashes exhibited the lowest values for both layer thicknesses (p < 0.05). Flexural strength was generally higher in specimens fabricated with 100 µm layer thickness; however, this effect was statistically significant only at the 8000-flash curing condition (p < 0.05). The lowest flexural strength values were recorded in the 2000-flash curing group (p < 0.05). Thermal aging did not significantly affect flexural strength or water sorption/solubility; however, a significant reduction in surface roughness was observed only under the 100 µm–2000-flash condition (p < 0.05). Conclusion: Specimens cured with 4000 flashes demonstrated superior physical and mechanical properties. Insufficient curing (2000 flashes) resulted in inferior material performance, whereas no consistent trend of improvement or deterioration was observed with excessive curing (8000 flashes). Keywords: Additive Manufacturing; CAD/CAM; 3D Permanent Resin; 3D Printing; Post-Printing Curing