The effect of repeated baking of porcelain on its bonding strength to a Co-Cr alloy 3D-printed by selective laser melting.

OBJECTIVES: This study aimed to evaluate the effect of multiple baking cycles of porcelain on its shear bond strength to a cobalt-chromium (Co-Cr) alloy that is three-dimensionally printed using Selective Laser Melting (SLM) technique.

MATERIALS AND METHODS: The research sample comprised forty-eight discs measuring 5 mm × 3 mm, divided into four groups according to: the manufacturing method (SLM, casting) and the number of porcelain baking cycles (1, 3) as follows: Group A: Co-Cr alloy by SLM with one baking cycle; Group B: Co-Cr alloy by SLM with three baking cycles; Group C: Ni-Cr alloy by casting with one baking cycle; Group D: Ni-Cr alloy by casting with three baking cycles. Then, porcelain was melted on disks, shear testing was performed and the values of the Shear Bond Strength (SBS) in MegaPascals (MPa) were calculated.

RESULTS: The mean SBS values for each group were (A: 25.69 - B: 19.51 - C: 35.72 - D: 28.67 MPa). Statistical analysis showed that the manufacturing method and the number of porcelain baking cycles had a significant influence on shear bond durability (P > 0.05): the strength of this bond decreased when baking cycles increased. The Co-Cr samples manufactured by SLM also showed a decrease in binding strength compared to the Ni-Cr samples made by casting.

CONCLUSION: Repeated baking of porcelain reduces the strength of the porcelain bond with the Co-Cr alloy made by Selective Laser Melting (SLM) technique.