Effect of soldering method on tensile strength of gold-palladium ceramic alloy
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The present study was designed to compare the tensile strength obtained by microwave post-ceramic soldering, conventional post-ceramic soldering, and laser post-ceramic welding. Specific aims were to compare tensile strength (measured by Instron Universal testing machine) and study representative fracture surfaces (observed with the help of SEM sections). The research hypothesis was the tensile strength of microwave post-ceramic soldering is comparable or superior to that of conventional post-ceramic soldering, and the laser post ceramic welding. Gold - Palladium ceramic alloy (Evolution lite, Ivoclar-Vivadent. Inc) and gold based solder were used in this study. Twenty seven wax samples were cast in Au-Pd alloy and randomly divided into four groups as follows: (1) laser welding with a specific post filler alloy (Laser ceramic white .5mm wire, Ivoclar-Vivadent Inc), (2) microwave soldering with a post ceramic solder (.585 Fine gold solder, Ivoclar Vivadent Inc.), (3) conventional soldering (Programat P200, Ivoclar vivadent Inc.) with the same post-ceramic solder used in the microwave soldering group, (4) control. All specimens were heat treated to simulate normal porcelain sintering sequence (IPS d.SIGN, Ivoclar Vivadent Inc.). The tensile strength of the four groups was measured by an Instron Universal Testing Machine. Results were analyzed statistically using one way analysis of variance (ANOVA). The surface and fracture sites of specimens were randomly selected and subjectively evaluated for fracture type and porosities using scanning electron microscope. A significant difference in tensile strength was found among all four groups. The control group showed the highest tensile strength, followed by the microwave, conventional, and laser welding group. The microwave and conventional (furnace) solder joints presented varying degrees of porosity and a combination of ductile and brittle fractures. Control specimens showed a homogeneous ductile fracture with no contamination or inclusions. However, the laser-weld samples showed large voids at the middle of the joint surface that were surrounded with ductile fracture pattern. Higher tensile strength was found for gold-palladium alloys soldered using microwave soldering than for either conventional soldering or laser welding. Conventional soldering resulted in higher tensile strength than laser welding. Pending a clinical validation of these results, it appears that, under the experimental conditions described, either microwave or conventional post-ceramic soldering satisfies ordinary clinical requirements related to tensile strength.