Influence of Multiple Castings and Surface Treatments on Metal-Ceramic Bond Strength and Surface Composition Variations of Nickel-Chromium (Ni-Cr) Alloy

Aim The aim of this study was to investigate the effect of multiple castings of nickel-chromium (Ni-Cr) base metal alloy and surface treatment on the metal-ceramic shear bond strength and surface chemical composition. Material and methods A total of 108 specimens (5 × 10 mm) were prepared and divided into six groups (n = 18). Three groups of Ni-Cr (4-all; Ivoclar, Schaan, Liechtenstein) alloy specimens (5 × 8 mm) were cast as follows: 100% fresh alloy (C0), addition of 50% by weight remnant of C0 (C1), and addition of 50% by weight remnant of C1 (C2). Within each alloy group, half of the specimens were treated with oxidative heat treatment only (S0), and the remaining half were treated with oxidative heat treatment combined with air abrasion (S1). Feldspathic ceramic (IPS Classic Ceramic; Ivoclar) was applied (5 × 2 mm), and shear bond strength was evaluated using a universal testing machine. Fracture surfaces were analyzed with a stereomicroscope. One specimen from each group was further evaluated for surface composition using scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectrometry (EDS). Data were analyzed using two-way ANOVA followed by the post hoc Tukey test with Bonferroni's correction. Results Group C0 exhibited the highest mean shear bond strength, followed by C1, which was not significantly different. Both groups had significantly higher values compared to C2 (P < 0.05). Fracture modes were predominantly mixed in C0 and C1, whereas C2 showed a higher frequency of adhesive failures. SEM-EDS analysis revealed a gradual decline in molybdenum (Mo) and Cr content with successive recasting. Conclusions Recasting up to one generation with 50% fresh alloy supplementation maintains clinically acceptable metal-ceramic bond strength. Recasting beyond the first generation significantly compromises bond integrity. Group S1 showed higher bond strength than Group S0; however, the difference was not statistically significant, and its advantage remains uncertain.