Influence of shaking method, shaking time, and frequency of resin reuse on the flexural strength of 3D-printed fixed restoration resins.

backgroundThe manipulation and handling of three-dimensional (3D) printing liquid resins prior to printing have not been reported in the literature. Therefore, this study was designed to assess the effect of different shaking methods and shaking times, together with the number of times the resin bottle was opened for resin reuse on the flexural strength (FS) of 3D-printed specimens, in conditions simulating routine laboratory handling protocols.

methodsTwo different resins (ASIGA DentaTOOTH and NextDent C&B MFH) were used for specimens' fabrication. Rollers and horizontal shakers were used to shake the resins for 30 and 60 min before printing. A total of 240 specimens were fabricated and grouped according to shaking method (roller and horizontal) and shaking time (30 and 60 min). Further subdivisions were performed according to resin reuse cycles. The resins were reused at defined 7-day intervals, with each resin bottle reopening considered one reuse cycle, resulting in three groups: first use, second use, and third use (n = 10). Bar-shaped (25 × 2 × 2 mm) specimens were printed according to manufacturers' recommendations and thermally cycled (5000 cycles), followed by 3-point bending test for FS testing. Data analysis was performed by using two-independent samples T-test, One-Way ANOVA and K-factors ANOVA. P-values less than 0.05 were considered statistically significant.

resultsK-factors ANOVA results indicated that repeated opening and reuse × material, shaking time × shaker, shaker × material, and shaking time × shaker × material all had significant interacting effects on the flexural strength (p < 0.001). For ASIGA, the roller shaker significantly produced higher FS values across all groups at 60 min shaking time (p < 0.001), but this effect was absent at 30 min shaking time. First use showed significantly higher FS compared to third use at 30-minute shaking time for both shakers (roller, p = 0.005; horizontal, p = 0.004). However, at 60-minute shaking time, no significant differences in FS were observed between the different reuse groups (p > 0.05). For NextDent, no significant differences were found between the two shakers for any reuse groups at either shaking times (p > 0.05). However, first use consistently demonstrated higher FS than second and third uses for both shaking times and shakers (p < 0.001). ANOVA revealed significant interactions among material types, shaking method, shaking time, and reuse cycle on FS (p < 0.001). For ASIGA resin, the roller shaker improved FS at 60 min shaking time, whereas no shaker-related differences were observed at 30 min. FS decreased with repeated use, particularly at shorter shaking times. For NextDent resin, shaker type had no significant effect; however, FS progressively decreased with repeated use cycles regardless of shaking conditions.

conclusionResin type, shaking method, shaking time, and repeated bottle opening significantly influenced the FS of 3D-printed resin. Proper resin handling may therefore help maintain the mechanical performance of 3D-printed resins.