Bonding characteristics of cast magnetic keeper to dental alloys

Objectives: To examine the bond strength of the Fe-Pt magnetic keeper laser-welded to dental alloys. Materials and Methods: Three alloys were used: Type IV gold (Sofard, Tokuriki Co.), Ag-Au (New Gold Para, Morita Corp.) and Co-Cr (Vitallium, Austenal) alloys. Plastic plate patterns (1.0x3.0x10.0 mm³) were cast for each alloy and the Fe-Pt keeper (Fe-36at%Pt). After polishing, the cast plate of each alloy was mounted in a jig, abutted to the Fe-Pt keeper and laser-welded (Neolaser L, Girrbach) under constant conditions at 200V (voltage) and 10ms (pulse duration). Five overlapped laser pulses (diam: 1.0 mm) were bilaterally applied to cover the joint width of the specimens (3.0 mm). Homogeneously welded and non-welded control specimens (1.0x3.0x20 mm³) for each alloy were also prepared. Tensile testing (n=5) was conducted with a universal testing machine (crosshead speed: 1 mm/min, gauge length: 10mm). The fracture force (Ff, N) and the elongation (%) were recorded and statistically analyzed using ANOVA (a=0.05). Results: In the control group, the greatest failure load was obtained for Co-Cr (1107±86N), followed by Ag-Au (993±68N), Type IV (802±36N) and Fe-Pt (575±14N)(each was significantly different than the others). The homogeneous weld group showed a tendency similar to the control group except for Co-Cr (465±97N) which was lower than Ag-Au (600±59N) and Type IV (536±48N). Homogeneous Fe-Pt showed the lowest Ff value (71±14N). All of the Ff values for the heterogeneous alloy/Fe-Pt group fell between homogeneous weld alloys and Fe-Pt. The highest value was obtained for Type IV (355±35N) which was significantly greater than Co-Cr (265±69N) and Ag-Au (186±29N). The results of elongation showed a tendency similar to the Ff results. Conclusion: To laser-weld to the Fe-Pt keeper, Type IV gold alloy could be a good candidate because of its great bond strength. Supported by Magnetic Health Science Foundation.