Effect of hatch distance on porcelain bond strength of metal frameworks produced by selective laser melting

The hatch distance, which refers to the spacing between adjacent laser lines in the laser melting process, may influence the microstructure of the metal framework and, hence, the metal-ceramic bond strength. However, studies on the influence of hatch distance on metal-ceramic bond strength are lacking.

The purpose of this in vitro study was to investigate the porcelain bond strength of cobalt chromium frameworks fabricated using selective laser melting with hatch distances of 50 µm, 55 µm, and 60 µm.

Bar-shaped cobalt chromium frameworks were fabricated using selective laser melting with hatch distances of 50 µm (Group-50), 55 µm (Group-55), and 60 µm (Group-60). After porcelain application, the metal-ceramic bond strength was evaluated using a 3-point bend test according to the International Organization for Standardization (ISO) 9693-1 standard. After the 3-point bend test, elemental analysis was performed on both the metal and porcelain interfaces of 1 randomly selected specimen from each group, and the density of 1 metal framework from each group was determined using the Archimedes method. In addition, microstructural analysis was performed on 1 metal framework from each group using optical microscopy, while 1 porcelain-applied metal framework was analyzed using scanning electron microscopy. The metal-ceramic bond strength data were statistically analyzed using a 1-way analysis of variance (α=.05) RESULTS: Hatch distance significantly affected the metal-ceramic bond strength (P<.001). Group-50 exhibited the highest mean ±standard deviation metal-ceramic bond strength (32.99 ±3.17 MPa), which was significantly higher than Group-55 (29.98 ±2.41 MPa; P<.001) and Group-60 (29.33 ±1.83 MPa; P<.001). No significant difference was found between Group-55 and Group-60 (P=.83). The elemental analysis indicated the absence of metal alloy components Co, Cr, Mo, and W on the porcelain side of the fracture interface across all groups. The proportions of porcelain composition elements Si, Ce, Ti, Zr, K, Al, Na, and Ca detected on the metal side of the fracture interface were consistent among the groups. As the hatch distance increased, the density of the frameworks decreased while porosity within the frameworks increased. The densities of Group-50, Group-55, and Group-60 were calculated as 8.28 g/cm³, 8.14 g/cm³, and 8.06 g/cm³, respectively.

The results revealed that hatch distance may affect the metal-ceramic bond strength and microstructure of cobalt chromium frameworks.