Surface morphology, printing accuracy and flexural strength of 3D-printed zirconia posts with longitudinal microgrooves

Postcore restoration is essential for compromised teeth. Zirconia is a promising material due to its esthetics, strength, and radiopacity. Additive manufacturing, particularly advanced customized jetting (ACJ) technology, enables the fabrication of complex microstructures on zirconia surfaces to potentially enhance resin bonding. However, before bonding tests, it is necessary to establish the printability, accuracy, and baseline mechanical properties of such microstructured posts.

A commercial fiber post was scanned and used as a template to design zirconia posts with 4, 8, 16, and 32 longitudinal microgrooves (MZ4, MZ8, MZ16, MZ32). Posts were fabricated via ACJ 3D printing. Surface morphology and roughness were evaluated via laser scanning confocal microscopy (LSCM). Microstructural surfaces were observed via scanning electron microscopy (SEM). Printing accuracy was assessed by boundary dimension and coefficient of variation (CV) of microgroove width. Flexural strength was determined via three-point bending test (ISO 6872:2024). Data were analyzed using Welch's ANOVA (α=0.05).

LSCM and SEM revealed regular, intact microgrooves in MZ4, MZ8, and MZ16, while MZ32 exhibited structural collapse. Surface roughness increased significantly from MZ4 to MZ16. Boundary dimensions of MZ4-MZ16 showed no significant differences, whereas MZ32 deviated significantly (P<0.01). CV values for MZ4, MZ8, and MZ16 were 10.30±3.38%, 12.99±4.44%, and 11.03±0.72%, respectively, with no significant intergroup differences (P=0.862). Flexural strengths for MZ4, MZ8, MZ16, MZ32, and the fiber post control were 605.32±27.48, 466.28±20.51, 414.28±33.69, 367.36±21.28, and 471.53±22.95 MPa, respectively. Welch's ANOVA revealed a significant difference (P=0.045), with a monotonic decreasing trend in strength as groove density increased. Significant difference was found only between MZ4 and MZ32 (P=0.037), while no significant differences were detected among other groups (P>0.05).

Within the limitations of this study, ACJ printing can reliably fabricate zirconia posts with up to 16 microgrooves without compromising accuracy or flexural strength. MZ16, which provided the highest surface roughness without significant loss of strength or accuracy, may be considered as a candidate for future adhesion studies. Further investigations-including bond strength testing, mechanical aging, and fatigue evaluation-are warranted.