Effect of soldering on the metal-ceramic bond strength of an Ni-Cr base alloy

Statement of problem

Although soldering is a common laboratory procedure, the use of soldering alloys may adversely affect metal-ceramic bond strength and potentially decrease the longevity of metal-ceramic restorations.

Purpose

The purpose of this study was to investigate the effect of soldering on metal-ceramic bond strength of a representative Ni-Cr base metal alloy.

Material and methods

Twenty-eight rectangular (25 × 3 × 0.5 mm) Ni-based alloy (Wiron 99) specimens were equally divided into soldering (S) and reference (R) groups. Soldering group specimens were covered with a 0.1-mm layer of the appropriate solder (Wiron-Lot) and reduced by 0.1 mm on the opposite side. Five specimens of each group were used for the measurement of surface roughness parameter (R_z) and hardness, and 3 were used for measurement of the modulus of elasticity. Six specimens of each group were covered with porcelain (Ceramco 3) and subjected to a 3-point bending test for evaluation of the metal-ceramic bond strength according to the ISO 9693 specification. The data from surface roughness, hardness, modulus of elasticity, and metal-ceramic bond strength were analyzed statistically, using independent t tests (α=.05).

Results

Statistical analysis of the R_z surface roughness parameter (S: 3.4 ± 0.3 μm; R: 3.7 ± 0.7 μm; P=.07) and bond strength (S: 46 ± 3 MPa; R: 40 ± 5 MPa; P=.057) failed to reveal any significant difference between the 2 groups. The specimens of the soldering group demonstrated significantly lower values both in hardness (S: 128 ± 11 VHN; R: 217 ± 4 VHN; P<.001) and in modulus of elasticity (S: 135 ± 4 GPa; R: 183 ± 6 GPa; P=.035) than the reference group.

Conclusion

Under the conditions of the present study, the addition of solder to the base metal alloy did not affect the metal-ceramic bond strength.