Effect of Printing Orientation and Surface Treatment on the Surface Roughness, Shear Bond Strength, and Flexural Strength of 3D-Printed Provisional Restoration Materials: An In Vitro Study.

Abstract

Objective: This study aimed to evaluate the influence of printing orientation and surface treatment on the surface roughness, shear bond strength (SBS), and flexural strength of 3D-printed provisional resin materials under laboratory conditions.

Materials and methods: Four printing orientations (0, 45, 60, and 90°) and four surface treatments (no treatment, airborne particle abrasion, tetrahydrofuran, and HC primer) were investigated. A total of 320 specimens were fabricated and tested according to ISO standards. Of these, 240 disk-shaped specimens were used for surface roughness assessment, conducted using a non-contact profilometer, and for SBS evaluation through a notched-edge shear test. Additionally, 80 rectangular bar specimens were subjected to three-point bending for flexural strength assessment. Fracture morphology was examined using scanning electron microscopy (SEM).

Statistical analysis: Normality and homogeneity of variance were verified using the Kolmogorov-Smirnov and Levene's tests. Surface roughness and SBS were analyzed using two-way ANOVA with Tukey's post hoc test, while flexural strength was analyzed using one-way ANOVA (α = 0.05).

Results: Printing orientation and surface treatment significantly affected the tested properties. Surface roughness varied according to orientation and treatment, with the 45° orientation exhibiting higher Ra values compared with other orientations. SBS values differed significantly among surface treatments and orientations, with higher bond strength observed in specimens treated with HC primer at 60°. Flexural strength was significantly greater at 60° compared with 90°. SEM analysis revealed more homogeneous interlayer integration at 60° and evident interlayer separation at 90°.

Conclusion: Within the limitations of this in vitro study, printing orientation and surface treatment significantly affected the surface and mechanical properties of the tested 3D-printed provisional resin. A 60° printing orientation combined with chemical surface conditioning demonstrated favorable laboratory performance. Further studies incorporating aging and fatigue protocols are required to confirm these findings.