Influence of printing procedure and printing axis of dental alloys on dimensional accuracy, surface roughness, and porosity

Abstract

Objectives: This study aimed to evaluate the printing procedure and printing axis and its influence on the dimensional accuracy, surface roughness, porosity, and strength of 3D-printed dental alloys used in orthodontics prepared using binder jetting (BJ), electron beam melting (EBM), or selective laser melting (SLM). Material and Methods: Specimens with a dimension of 50 mm × 12 mm were produced using BJ, EBM, and SLM techniques of dental alloys and were printed either along the X-, Y-, or Z-axis (n = 8 per group). Specimen dimension was chosen according to the ISO standard 6892-1 for tensile strength test specimens. Surface roughness parameters Sa, Sz, Sq, and Ssk were obtained using a 3D laser microscope and porosities were visualized with scanning electron microscopy (SEM). The specimen surfaces were optically scanned and volumetric deviations from the original stereolithography files were calculated. Afterward, tensile strength was measured. Results: The printing method and printing axis significantly affected surface roughness parameters (P < 0.05). Overall, the lowest surface roughness Sa values were found for BJ (9.1 ± 3.4 µm) followed by SLM (39.8 ± 24.2 µm) and EBM (50.4 ± 6.4 µm). BJ showed the smallest dimensional deviation followed by EBM and SLM. SEM analysis revealed a porous structure of BJ while fewer pores were observed on EBM and SLM samples. The ultimate tensile strength was only determined for BJ (495 ± 6 MPa) and EBM (726 ± 50 MPa) as the strength of SLM superseded the strength of the holder of the universal testing machine. Conclusion: BJ printing provides the highest dimensional accuracy with the smoothest surfaces irrespective of the printing axis. However, the remaining porosities owed to this printing procedure may have decreased the strength of the material.

Clinically Relevant Properties of 3D Printable Materials for Intraoral Use in Orthodontics: A Critical Review of the Literature

“…With regard to metal printed devices, it emerged from this literature review that few investigations focused on the properties of 3D-printed alloys, although the digital workflow for their production has been described in the literature [ 7 , 61 , 62 , 63 , 64 ], and considered as a simplification compared to the analog procedures [ 61 ]. In addition to avoiding patient discomfort with conventional impression-taking techniques and eliminating the need for a physical model, with 3D-printed metallic appliances, the step of teeth separation can also be skipped, as the structures do not extend in interdental spaces [ 61 ].…”

“…With regard to metal printed devices, it emerged from this literature review that few investigations focused on the properties of 3D-printed alloys, although the digital workflow for their production has been described in the literature [ 7 , 61 , 62 , 63 , 64 ], and considered as a simplification compared to the analog procedures [ 61 ]. In addition to avoiding patient discomfort with conventional impression-taking techniques and eliminating the need for a physical model, with 3D-printed metallic appliances, the step of teeth separation can also be skipped, as the structures do not extend in interdental spaces [ 61 ]. The versatility of digital design, allowing the production of multitasking appliances, the possibility to create a digital library, streamlining the design process, the remote communication with the laboratory or other practitioners, and widening the opportunities for cooperation have been indicated as advantages of 3D-printing metal appliances [ 61 ].…”

“…In addition to avoiding patient discomfort with conventional impression-taking techniques and eliminating the need for a physical model, with 3D-printed metallic appliances, the step of teeth separation can also be skipped, as the structures do not extend in interdental spaces [ 61 ]. The versatility of digital design, allowing the production of multitasking appliances, the possibility to create a digital library, streamlining the design process, the remote communication with the laboratory or other practitioners, and widening the opportunities for cooperation have been indicated as advantages of 3D-printing metal appliances [ 61 ]. Among the disadvantages of the technology, the restricted choice of available alloys, their rigidity, and the current inability to print multiple alloys have been mentioned [ 61 ].…”

“…The versatility of digital design, allowing the production of multitasking appliances, the possibility to create a digital library, streamlining the design process, the remote communication with the laboratory or other practitioners, and widening the opportunities for cooperation have been indicated as advantages of 3D-printing metal appliances [ 61 ]. Among the disadvantages of the technology, the restricted choice of available alloys, their rigidity, and the current inability to print multiple alloys have been mentioned [ 61 ]. The stiffness of the alloys makes any minor mistake in the design and manufacture of the appliances quite unforgiving and makes rather difficult any chairside or intraoral adjustment through wire bending [ 61 ].…”

“…Among the disadvantages of the technology, the restricted choice of available alloys, their rigidity, and the current inability to print multiple alloys have been mentioned [ 61 ]. The stiffness of the alloys makes any minor mistake in the design and manufacture of the appliances quite unforgiving and makes rather difficult any chairside or intraoral adjustment through wire bending [ 61 ]. Additionally, the removal can be difficult with conventional band-removing tools, as 3D-printed devices typically exhibit good fit and smooth structures.…”