Flexural strength of 3D-printed nanocomposite provisional resins: Impact of SiO2 and ZrO2 nanoparticles and printing orientations in vitro

Purpose: The aim of this study was to investigate and compare the influence of zirconium dioxide nanoparticles (ZrO(2)NPs) and silicon dioxide nanoparticles (SiO(2)NPs) addition and printing orientation on the flexural strength (FS) of provisional three-dimensional (3D) printing resins undergoing thermal cycling (TC). Methods: Three dimensional-printed resin (NextDent C&B MFH) was used to fabricate 300 bar-shaped specimens (25 x 2 x 2 mm(3)). The ZrO(2)NPs and SiO(2)NPs specimens were divided into two groups, then subdivided into three groups, based on the nanoparticle concentration (i.e., 0 wt% (original group), 0.5 wt%, and 1 wt%). Each concentration was printed in three printing orientations (0 degrees, 45 degrees, and 90 degrees). The printed specimens were exposed to 5000 cycles of TC, followed by a three-point bending test to assess the FS. Fracture surface analysis was conducted by using a scanning electron microscope (SEM). For data analysis, ANOVA and Tukey's post hoc were utilized (alpha = 0.05). Results: Compared to the original material, the addition of ZrO(2)NPs and SiO(2)NPs had a significantly positive impact on the FS, (P > 0.001). After TC, the FS of the original group decreased significantly and had the lowest value. The highest FS value was observed in 1% ZrO(2)NPs at 0 degrees. Regardless of the nanoparticle concentration, the 0 degrees orientation consistently showed a higher FS, compared to the 45 degrees and 90 degrees orientations. At all orientations (i.e., 0 degrees, 45 degrees, and 90 degrees), the FS significantly increased with the addition of NPs, compared with that of the original material (P > 0.001). TC had a significantly negative effect on the FS of the unmodified groups. However, no significant differences existed in FS among the modified groups after TC. Conclusion: The addition of SiO(2)NPs and ZrO(2)NPs increased the FS of the 3D-printed provisional resin. Regardless of the nanoparticle concentration, the 0 degrees orientation had the higher FS. TC had an effect on the original resin, whereas it had no significant effect on the nanoparticle-modified resins. In clinical practice, 3D-printed provisional nanocomposite resins printed at the 0 degrees orientation could be recommended for long-term dental provisional restorations.