Available online 11 April 2024

The surface topography of metal substrate can affect its bond to porcelain. A neodynium-doped yttrium aluminum garnet (Nd:YAG) laser has been introduced to modify the metal surface topography and improve porcelain bond strength. However, studies on the effect of laser etching on metal to porcelain bond strength are lacking.

The purpose of this in vitro study was to determine the effect of Nd:YAG laser etching on the surface roughness and wettability of and the porcelain bond strength to cobalt chromium (Co-Cr) substrate fabricated by milling and direct metal laser sintering (DMLS).

Thirty-two 0.5×3×25-mm Co-Cr specimens were fabricated by milling soft Co-Cr (M group) and DMLS Co-Cr metal powder (DML group). The surface topography of representative specimens from each study group was assessed under a scanning electron microscope (SEM) and an atomic force microscope (AFM). All specimens were assessed for surface roughness using a contact profilometer, and for wettability with a contact angle goniometer. Half of the specimens of each study group (n=8) were subjected to surface laser etching by using a Nd:YAG laser. The specimens subjected to etching were assessed again for surface topography and wettability. All specimens in both study groups were veneered with porcelain. The porcelain bond strength was tested with a 3-point bend test in a universal testing machine. The results were statistically analyzed with 2-way ANOVA test followed by the post hoc Tukey test for pairwise comparisons (α=.05).

After etching, the M group had a higher mean ±standard deviation Ra and Rz of 2.9 ±0.6 and 17.7 ±3.2 µm and significantly better wettability and bond strength of 79 ±6 and 52 ±13 MPa. In contrast, after etching, the DMLS group had a significantly lower Ra and Rz of 7.9 ±2.4 and 41.8 ±9.3 µm and significantly lower wettability and bond strength of 87 ±4 and 70 ±10 MPa. The DMLS group had a significantly higher roughness and bond strength than the M group before and after laser etching. The SEM and AFM showed different surface topography in the study groups.

The manufacturing process of Co-Cr substrate had a significant effect on surface characteristics and porcelain bond strength. Laser etching improved the surface topography and bond strength of milled Co-Cr but not of DMLS Co-Cr.

Thirty-two rectangular 0.5×3×25-mm Co-Cr specimens were manufactured from a CAD design according to the International Organization for Standardization (ISO) 9693–1 standard.24 The CAD design of the specimens was conducted by using a software program (Blender version 2.77a; The Blender Foundation). The specimens were fabricated using 2 different methods: milling soft Co-Cr (M group) and DMLS Co-Cr metal powder (DML group). A sample size of 16 specimens per group was calculated by using a

The 2-way ANOVA test indicated that the manufacturing method and surface treatment had a significant effect on the surface characteristics and the porcelain bond strength (P˂.001). Table 2 summarizes the results of the surface roughness, the surface wettability represented as contact angle, and the porcelain bond strength for study groups. For the M group, laser etching did not have a significant effect on surface roughness (P>.05). However, the wettability and bond strength significantly

This study aimed to assess the effect of the manufacturing process of Co-Cr framework for metal-ceramic restorations on the surface characteristics and the porcelain bond strength before and after laser etching. The null hypotheses that no significant differences would be found in the surface roughness, wettability, or porcelain bond strength between milled and direct metal laser sintered Co-Cr before and after laser etching was rejected as the manufacturing process had a significant effect on

Based on the findings of this in vitro study, the following conclusions were drawn:

DMLS Co-Cr alloy had significantly higher surface roughness and porcelain bond strength compared with milled Co-Cr before and after laser etching.

Nd:YAG laser etching increased surface roughness and significantly improved the wettability and porcelain bond strength of milled Co-Cr.

The Nd:YAG laser etching used in this study significantly reduced the surface roughness, wettability, and porcelain bond strength of

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