Can postpolymerization for 3D-printed interim restorations be improved?

Postpolymerization methods influence the properties of 3-dimensionally (3D) printed materials. Nevertheless, it is a time-consuming step that could lead dentists to avoid the chairside use of 3D printing. Information assessing the impact of different postpolymerization workflows on flexural strength and color stability is sparse. The purpose of this in vitro study was to analyze the impact of different postpolymerization methods on the flexural strength and color stability of 3D-printed resins used for interim restorations. Three resin materials: CT (Cosmos Temp; Yller Biomaterials), DT (Denture Teeth; Formlabs), and CB (C&B MFH; NextDent) were submitted to 4 methods of postpolymerization: a Form Cure polymerization chamber (FC) (Form Cure; Formlabs), a broadband LED device (Valo Grand; Ultradent Products, Inc) operating at 1000 mW/cm2 for 2 different polymerization times (40 seconds/V40 or 120 seconds/V120), and a custom-made polymerization chamber with a 24 W UV LED Strip (CC). The specimens were assessed for flexural strength using an universal testing machine immediately after polymerization or after 10 000 thermal cycles, and the color stability was evaluated using a spectrophotometer at baseline, after 7 days in dark, dry storage at 37 °C and after 24 hours of artificial aging in water at 60 °C. The data were evaluated using 3-way ANOVA (flexural strength) and 3-way repeated measurements ANOVA (color stability), followed by the Tukey HSD test (α=.05). Flexural strength showed significant differences for resin, postpolymerization method, time, and for the interaction between all effects. CT showed the highest overall flexural strength, while DT showed the lowest. In general, V120 produced specimens with higher flexural strength. Thermocycling did not reduce flexural strength except for CB polymerized with FC and V120, and DT polymerized with V40. For color stability, significant differences were found for resin, postpolymerized method, time, and for the interaction between all effects. The highest ΔE values were observed for DT polymerized using V40 after artificial aging. The lowest values were observed for the same resin but polymerized using V120 after 7 days in dark, dry storage at 37 °C. Postpolymerization with the broadband LED device for 120 seconds can produce specimens with higher flexural strength values and higher color stability when compared with the other postpolymerization workflows tested in this study.