Effect of postpolymerization on the wear behavior of additively manufactured definitive crown resins

Additively manufactured definitive crown ceramic-reinforced composite (DC-CRC) resin materials have been increasingly used in clinical dentistry. However, their mechanical performance depends on postpolymerization parameters. Limited evidence is available regarding the influence of different postpolymerization techniques on the wear behavior of DC-CRC materials.

The purpose of this in vitro study was to evaluate the effects of several postpolymerization techniques and durations on the wear volume of additively manufactured DC-CRC specimens after thermomechanical aging and to compare these outcomes with those of a subtractively manufactured hybrid ceramic.

Disk-shaped specimens (Ø12×2 mm) were digitally designed and fabricated either from a hybrid ceramic block (Vita Enamic) by milling (Group VE, n=10) or from definitive crown resin (Saremco Crowntec) using a digital light processing (DLP) 3-dimensional (3D) printer (n=50). Printed specimens were assigned to 5 postpolymerization protocols: ultraviolet (UV) light polymerization for 30 minutes (Group Sx1), UV-light polymerization for 2×30 minutes (Group Sx2), otoflash polymerization in a nitrogen atmosphere using 2×2000 flashes (Group Nx1), otoflash polymerization in a nitrogen atmosphere using 4×2000 flashes (Group Nx2), and light-emitting diode (LED) light polymerization for 2×40 seconds (Group LED). All specimens were finished and polished according to the manufacturer's instructions and subjected to thermomechanical aging in a mastication simulator (50 N, 240 000 cycles, 5 to 55 °C). Pre-aging and post-aging digital scans were obtained with a laboratory scanner. Wear volume (mm³) was calculated by aligning STL files and performing a 3D analysis. Statistical evaluation was performed using 1-way ANOVA, followed by the Tukey post hoc test for multiple comparisons (α=.05).

A significant difference in wear volume was found among the groups (P<.001). The hybrid ceramic (VE) exhibited the lowest mean ±standard deviation wear (0.12 ±0.05 mm³), whereas the highest wear was observed in the UV-polymerized Sx1 group (0.33 ±0.09 mm³). The wear in Sx1 was significantly greater than in Nx2 and VE. No significant differences were found between the Sx1 and Sx2 groups and between the Nx1 and Nx2 groups (P>.05). LED-polymerized specimens exhibited significantly greater wear than VE. Postpolymerization in the nitrogen atmosphere groups (Nx1 and Nx2) showed wear volumes comparable to those of the hybrid ceramic.

Postpolymerization techniques influenced the wear resistance of additively manufactured DC-CRC materials. Polymerization in a nitrogen atmosphere improved wear performance compared with that of subtractively manufactured hybrid ceramic. Extending polymerization duration showed no significant differences in wear within each method; however, prolonged polymerization in a nitrogen atmosphere showed better outcomes than standard UV-light polymerization. Postpolymerization in a nitrogen atmosphere may therefore enhance the clinical durability of 3D printed definitive resin crowns, although long-term and clinical investigations remain necessary.