Recycling selective laser melting alloy powder on cobalt chromium-to-ceramic bond strength

Reusing the powder in selective laser melting machines after multiple cycles is a cost-effective procedure for dental laboratories. However, information on the metal-ceramic bond strength of the framework fabricated by using recycled powder is lacking.

The purpose of this in vitro study was to investigate how the bonding agent and repeated alloy powder reuse affected the metal-ceramic bond strength of cobalt chromium frameworks fabricated by using selective laser melting.

Four square and 40-bar-shaped cobalt chromium frameworks were fabricated by selective laser melting. Half were produced by using virgin alloy powder (Group V; n_square=2, n_bar=20), and half with 30-times reused powder (Group R; n_square=2, n_bar=20). The particle size of each powder was measured by using scanning electron microscopy, and its phase composition was characterized by using radiograph diffraction. Each group was divided into 2 subgroups (Group W [Wash Opaque] and Group N [NP-Bond]) according to the brand of bonding agent used. After ceramic application, the metal-ceramic bond strengths were evaluated by using 3-point bend tests. The bonding agents' chemical composition was analyzed by using radiograph fluorescence. Bond strength data were analyzed by using a 2-way analysis of variance (α=.05).

Mean ±standard deviation bond strengths did not differ significantly (P>.05) between Groups V (31.25 ±4.65) and R (30.88 ±4.78). Group W (35.34 ±1.78) had significantly higher bond strength than Group N (26.80 ±1.74; P<.001). Radiograph diffraction analysis found that the phase composition of all powders was similar. The bonding agent in Group W contained cerium, whereas, that in Group N did not.

Metal-ceramic bond strength was unaffected by alloy powder reuse. However, the bonding agent brand may affect the bond strength of cobalt chromium frameworks fabricated by using selective laser melting.