Nanoparticle jetting 3D printing of zirconia: Optimized intaglio microstructures for achieving superior bonding performance and fracture resistance in fixed prosthodontics.

STATEMENT OF PROBLEM: Ultrathin 3-dimensionally (3D) printed zirconia restorations require optimized intaglio microstructures to balance bonding performance and fracture resistance; however, systematic data regarding surface morphology and depth for nanoparticle jetting (NPJ)-fabricated zirconia are lacking.

PURPOSE: The purpose of this in vitro study was to investigate the effects of surface-microstructural morphology and depth on the shear bond strength (SBS) and fracture load of NPJ 3D printed zirconia restorations and to optimize the surface-topography design for clinical use.

MATERIAL AND

METHODS

Zirconia specimens with 4 surface textures (circular, triangular, concentric circular, and undercut circular) and 4 depths (40, 60, 80, and 100 μm) were fabricated by NPJ additive manufacturing and conventional milling. Ultrathin zirconia complete crowns (0.5 mm thick) were prepared. The SBS and fracture load were tested with a universal material testing machine. The debonding modes and interfacial elemental composition were analysed by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). One-way analysis of variance (ANOVA) coupled with the Tukey HSD test was adopted for intergroup comparisons (α=.05).

RESULTS

The bonding performance and mechanical strength of nontextured NPJ-printed zirconia were similar to those of milled zirconia (P=.984). The surface microstructures significantly increased the bond strength, with the circular and undercut circular textures performing the best. The bond strength increased with depth and plateaued at 80 to 100 μm. For the 0.5-mm crowns, the fracture load decreased significantly with increasing depth (P<.001). The 60-μm circular microstructure balanced favorable SBS and mechanical stability, and all the groups satisfied clinical mechanical criteria under the International Organization for Standardization (ISO) 6872 graded standards.

CONCLUSIONS

NPJ technology enables precise control of the zirconia surface topography to increase bonding. For ultrathin prostheses, the 60-μm circular microstructure represented the optimal design that provided high bond strength and sufficient fracture resistance for clinical application.