Evaluation of flexural strength of additively manufactured resin materials compared to auto-polymerized provisional resin with and without hydrothermal aging.

Purpose: Additive manufacturing (AM) technologies are used to fabricate 3D-printed provisional dental restorations. The purpose of this study was to investigate the flexural strength of 3D-printed resins and compare their mechanical performance with those of conventional resins indicated for provisional restorations.

Materials and methods: This study included six different 3D-printed resin materials, namely (Nextdent (ND); Temp PRINT (TP); Optiprint temp (OT); 3Delta Etemp (DE); Saremco print | CROWNTEC (SA); MED690 (ST)), and one conventional (Protemp (PT)) (Control) provisional resin material. Specimens (N = 168) were prepared (25x2x2 mm³) following ISO 10477:2018 guidelines for temporary materials using a printer (Asiga MAX 3D). Post-processing was accomplished following each manufacturer's recommendation. While half of the specimens were tested after 24 H without aging, the other half was subjected to thermomechanical aging in a custom-made chewing simulator (1.200.000 cycles, 5 °C and 55 °C). Flexural strength of the specimens was determined using a Universal Testing Machine. Data were analyzed using two-way ANOVA followed by Tukey's post-hoc test (α = 0.05). Weibull modulus for each group was calculated based on parametric distribution analysis of censored data for maximum fracture load.

Results: No significant difference was observed in mean flexural strength (MPa) when non-aged and aged conditions were compared in the OT and PT groups (p>0.05). Groups ND, SA, TP, DE, and ST presented significant differences ranging between 12.67 and 57.39 MPa (p<0.05). All groups presented lower shape and scale values in aged groups compared to their non-aged counterparts. While OT and PT maintained their flexural strength after aging, ND exhibited the highest decrease (30%), followed by DE (23.8%), SA (16.2%), TP (12%), and ST (8.6%) in descending order. Weibull modulus decreased as a function of aging except in group ST.

Conclusion: Significant effect of themomechanical aging especially on ND and DE materials should be considered with caution when such materials are indicated as interim or long-term interim provisional restorations. SA and TP exceeded the expectations from a provisional material compared to that of the conventional control material PT.