Metal-ceramic bond strength of a cobalt chromium alloy for dental prosthetic restorations with a porous structure using metal 3D printing

Selective laser sintering (SLS) is a new type of additive material manufacturing technology. The development of precise 3D metal printing technology has enabled the printing of complicated metal structures, particularly in the medical field. Finding a way to integrate new technologies with Co–Cr alloys for the precision manufacturing of dental restoration materials and a way to improve the metal-ceramic bonding strength of the materials have become a key focus of dental restoration clinical trials. The purpose of this study is to evaluate bonding strength and ceramic adhesion between metal and ceramics using Co–Cr specimens with different porous structures manufactured using SLS technology. According to the international standard ISO9693:19992, we printed three sets of 10 rectangular Co–Cr alloy test specimens of the same size (25 × 3 × 0.5 mm) using an SLS-3D metal printer and fused a ceramic layer (8 x 3 × 1.1 mm) to the center of the Co-Cy alloy test specimen. Before testing, we conducted stress and fracture simulation analysis on three specimen types (no holes, circular-shaped holes, and rhombic-shaped holes), using ABAQUS results to predict the results of three-point bending tests. These simulation results were then compared with the experimental data. We used three-point bending tests to assess the bonding strength of the fabricated metal-ceramic bonding surface. We also used a digital microscope (100× and 200×) to observe the surface conditions of the samples. Finally, we analyzed the results using one-way analysis of variance. The ABAQUS bending simulations indicated that the bending energy decreased sequentially for the hole-free, circular-hole and rhombic-hole specimens. Similarly, when the three types of test specimen were manufactured using SLS, significant differences in bending energy were observed between the rhombic-hole specimens and both the hole-free (P < 0.05) and circular-hole specimens (P < 0.05). In addition, the bond strength for all groups was higher than the international minimum standard of 25 MPa (33.36 ± 3.17 MPa). In this research, the bond strength of all three metal-ceramic test specimens was higher than the international minimum standard of 25 MPa set by ISO1999/9693. However, the circular porous design did not show previous diversity with other porous shape design. In addition, due to limitations in the accuracy of 3D printing using SLS, the structural advantages our proposed specimen design are difficult to verify. Therefore, we plan to develop new structural designs to improve the bonding strength of metal-ceramic structures in future work.