Chulalongkorn University Dental Journal

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Objective To compare the ultimate tensile strength of the soldering joint from conventional torch technique and the welding joint from laser technology in three types of alloy, gold-palladium (Au-Pd) alloy, nickel-chrome (Ni-Cr) alloy and cobalt-chrome (Co-Cr) alloy using the ISO standard model. Materials and methods Fifty four specimens were prepared in accordance with ISO 6892 from three different alloys, Au-Pd alloy, Ni-Cr alloy and Co-Cr alloy. Six specimens of each alloy were cut and either soldered with gas propane-oxygen torch or welded with laser. The control group was six specimens without cutting (as cast specimens) of each alloy. All specimens were then undergone for thermocycling required for oxidation, opaque layer, dentine layer and glazing before testing. Specimens were tested for ultimate tensile strength (UTS) using universal testing machine. Scanning electron microscopy and energy dispersive x-ray microanalysis of the fractured surface were also obtained and evaluated. Results The means ultimate tensile strength of laser welding specimens were higher than those of torch soldering specimens in all alloy groups (mean laser welding in Au-Pd group = 422.51 MPa, mean torch soldering in Au-Pd group = 279.33 MPa, mean control in Au-Pd group = 548.54 MPa, mean laser welding in Ni-Cr group = 600.99 MPa, mean torch soldering in Ni-Cr group = 395.06 MPa, mean control in Ni-Cr group = 549.42 MPa, mean laser welding in Co-Cr group = 646.67 MPa, mean torch soldering in Co-Cr group = 453.68 MPa and mean control in Co-Cr group = 672.13 MPa). Data analysis using one-way ANOVA and Bonferroni's test indicated that there were statistically significant differences (p < .05) of UTS between laser welding and solder specimens in all alloy groups while there was no statistically significant difference (p < .05) of ultimate tensile strength between welding joint and as cast in Ni-Cr alloy and Co-Cr alloy group. Conclusion From this investigation, ultimate tensile strength of joint from laser welding technique was greater than that of a gas-propane oxygen torch soldering joint in Au-Pd, Ni-Cr and Co-Cr alloy.



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