Effect of Postrinsing Times and Methods on Surface Roughness, Hardness, and Polymerization of 3D-Printed Photopolymer Resin.

Objectives:  This in vitro study investigated the effects of different postrinsing times and methods on the surface roughness, surface hardness, and degree of polymerization of materials manufactured via stereolithography (SLA).

Materials and methods:  A total of 288 disk-shaped specimens were manufactured using an SLA three-dimensional (3D) printer. The specimens were randomly divided into nine groups (n = 32) based on rinsing times and methods. The groups were categorized into three rinsing methods: automated, ultrasonic, and hand washing, with rinsing times of 5, 10, and 15 minutes using a 99% isopropanol alcohol as a solvent. Linear roughness (Ra) and area roughness (Sa) were measured using a 3D confocal laser microscopy; the roughness morphology was evaluated by using scanning electron microscopy. Vickers hardness (VHN) tests were performed using a Vickers microhardness tester. Fourier-transform infrared spectrometry was used to determine the degree of conversion of treated specimens.

Statistical analysis:  Data were statistically analyzed using two-way analysis of variance. The post hoc Tukey tests were conducted to compare the differences between groups (p < 0.05).

Results:  The choice of the rinsing time and method affected the surface properties of the SLA photopolymer resin. The 15 minutes of ultrasonic method exhibited the highest Ra scores (0.86 ± 0.1 µm), while the 15 minutes of automated method presented the highest Sa scores (1.77 ± 0.35 µm). For the VHN test, the 15 minutes of ultrasonic method displayed the highest VHN score (18.26 ± 1.03 kgf/mm²). For the degree of polymerization, the 15 minutes of automated method was initially identified as the most effective (87.22 ± 6.80).

Conclusion:  To facilitate the overall surface roughness, surface hardness, and degree of polymerization, the optimal choice of postprocessing rinsing time and method for achieving a clear photopolymer resin was determined to be the ultrasonic method with a rinsing time of 15 minutes.