Effects of three soldering techniques on the strength of high-palladium alloy solder joints

Effects of soldering methods on tensile strength of a gold-palladium metal ceramic alloy

STATEMENT OF PROBLEM

The tensile strength obtained by conventional postceramic application soldering and laser postceramic welding may require more energy than microwave postceramic soldering, which could provide similar tensile strength values.

PURPOSE

The purpose of the study was to compare the tensile strength obtained by microwave postceramic soldering, conventional postceramic soldering, and laser postceramic welding.

MATERIAL AND METHODS

A gold-palladium metal ceramic alloy and gold-based solder were used in this study. Twenty-seven wax specimens were cast in gold-palladium noble metal and divided into 4 groups: laser welding with a specific postfiller noble metal, microwave soldering with a postceramic solder, conventional soldering with the same postceramic solder used in the microwave soldering group, and a nonsectioned control group. All the specimens were heat treated to simulate a normal porcelain sintering sequence. An Instron Universal Testing Machine was used to measure the tensile strength for the 4 groups. The means were analyzed statistically with 1-way ANOVA. The surface and fracture sites of the specimens were subjectively evaluated for fracture type and porosities by using a scanning electron microscope.

RESULTS

The mean (standard deviation) ultimate tensile strength values were as follows: nonsectioned control 818 ±30 MPa, microwave 516 ±34 MPa, conventional 454 ±37 MPa, and laser weld 191 ±39 MPa. A 1-way ANOVA showed a significant difference in ultimate tensile strength among the groups (F3,23=334.5; P<.001). Follow-up multiple comparisons showed a significant difference among all the groups. Microwave soldering resulted in a higher tensile strength for gold and palladium noble metals than either conventional soldering or laser welding.

CONCLUSION

Conventional soldering resulted in a higher tensile strength than laser welding. Under the experimental conditions described, either microwave or conventional postceramic soldering would appear to satisfy clinical requirements related to tensile strength.

Strength properties of preceramic brazed joints of a gold-palladium alloy with a microwave-assisted oven and gas/oxygen torch technique

STATEMENT OF PROBLEM

The effect of microwave brazing on the strength properties of dental casting alloys is not yet known.

PURPOSE

The purpose of this study was to compare the strength properties of preceramic brazed joints obtained by using a microwave oven and a conventional torch flame for a high noble alloy (Au-Pd).

MATERIAL AND METHODS

A total of 18 tensile bars made of an Au-Pd ceramic alloy were fabricated. Six specimens were cut and joined with a high-fusing preceramic solder in a specially designed microwave oven, and 6 specimens were joined with a conventional natural gas/oxygen torch. The remaining 6 uncut specimens were tested as a control. All the specimens were subjected to testing with a universal testing machine. A 1-way ANOVA was performed for each strength property tested.

RESULTS

The tensile strength of the uncut group was the highest (745 ±19 MPa), followed by the microwave group (420 ±68 MPa) and the conventional torch group (348 ±103 MPa) (P<.001); however, no significant difference in tensile strength was found between the microwave group and gas torch group. The tensile strength of the microwave group exceeded ANSI/ADA Standard No. 88, Dental Brazing Alloys (a joint standard of the American National Standards Institute and the American Dental Association).

CONCLUSIONS

The microwave heating preceramic solder method demonstrated the excellent tensile strength of an Au-Pd alloy and may be an alternative way of joining alloys when a torch flame is contraindicated.

Effect of soldering techniques and gap distance on tensile strength of soldered Ni-Cr alloy joint

PURPOSE

The present study was intended to evaluate the effect of soldering techniques with infrared ray and gas torch under different gap distances (0.3 mm and 0.5 mm) on the tensile strength and surface porosity formation in Ni-Cr base metal alloy.

MATERIALS AND METHODS

Thirty five dumbbell shaped Ni-Cr alloy specimens were prepared and assigned to 5 groups according to the soldering method and the gap distance. For the soldering methods, gas torch (G group) and infrared ray (IR group) were compared and each group was subdivided by corresponding gap distance (0.3 mm: G3 and IR3, 0.5 mm: G5, IR5). Specimens of the experimental groups were sectioned in the middle with a diamond disk and embedded in solder blocks according to the predetermined distance. As a control group, 7 specimens were prepared without sectioning or soldering. After the soldering procedure, a tensile strength test was performed using universal testing machine at a crosshead speed 1 mm/min. The proportions of porosity on the fractured surface were calculated on the images acquired through the scanning electronic microscope.

RESULTS

Every specimen of G3, G5, IR3 and IR5 was fractured on the solder joint area. However, there was no significant difference between the test groups (P > .05). There was a negative correlation between porosity formation and tensile strength in all the specimens in the test groups (P < .05).

CONCLUSION

There was no significant difference in ultimate tensile strength of joints and porosity formations between the gas-oxygen torch soldering and infrared ray soldering technique or between the gap distance of 0.3 mm and 0.5 mm.

Effect of temporal pulse shaping on the reduction of laser weld defects in a Pd-Ag-Sn dental alloy

OBJECTIVES

To describe the influence of pulse shaping on the behavior of a palladium-based dental alloy during laser welding and to show how its choice is effective to promote good weld quality.

METHODS

Single spots, weld beads and welds with 80% overlapping were performed on Pd-Ag-Sn cast plates. A pulsed Nd:Yag laser was used with a specific welding procedure using all the possibilities for pulse-shaping: (1) the square pulse shape as the default setting, (2) a rising edge slope for gradual heating, (3) a falling edge slope to slow the cooling and (4) a combination of a rising and falling edges called bridge shape. The optimization of the pulse shape is supposed to enhance weldability and produce defect-free welds (cracks, pores…) Vickers microhardness measurements were made on cross sections of the welds.

RESULTS

A correlation between laser welding parameters and microstructure evolution was found. Hot cracking and internal porosities were systematically detected when using rapid cooling. The presence of these types of defects was significantly reduced with the slow cooling of the molten pool. The best weld quality was obtained with the use of the bridge shape.

SIGNIFICANCE

The use of a slow cooling ramp is the only way to significantly reduce the presence of typical defects within the welds for this Pd-based alloy studied.

Bond strength of gold alloys laser welded to cobalt-chromium alloy

The objective of this study was to investigate the joint properties between cast gold alloys and Co-Cr alloy laser-welded by Nd:YAG laser. Cast plates were fabricated from three types of gold alloys (Type IV, Type II and low-gold) and a Co-Cr alloy. Each gold alloy was laser-welded to Co-Cr using a dental laser-welding machine. Homogeneously-welded and non-welded control specimens were also prepared. Tensile testing was conducted and data were statistically analyzed using ANOVA. The homogeneously-welded groups showed inferior fracture load compared to corresponding control groups, except for Co-Cr. In the specimens welded heterogeneously to Co-Cr, Type IV was the greatest, followed by low-gold and Type II. There was no statistical difference (P<0.05) in fracture load between Type II control and that welded to Co-Cr. Higher elongations were obtained for Type II in all conditions, whereas the lowest elongation occurred for low-gold welded to Co-Cr. This study indicated that, of the three gold alloys tested, the Type IV gold alloy was the most suitable alloy for laser-welding to Co-Cr.

Physical and metallurgical considerations of failures of soldered bars in bar attachment systems for implant overdentures: a review of the literature

The purpose of this literature review was to identify the etiological factors of failure of soldered bars in bar attachment systems for removable implant overdentures. A search of MEDLINE using the key words "bar attachment systems" was performed of English language peer-reviewed journals published between 1975 and 2005. Clinical studies of implant overdentures with prosthodontic maintenance complications of bar attachment systems were identified to establish the perceived etiology of failure. A further search of MEDLINE using the key words "solder joint" was also performed of the fixed prosthodontic literature to identify specific factors affecting the strength, fatigue resistance, and quality of gold solder joints used for bar attachment systems. The first search on bar attachment systems produced evidence of low failure rates of interabutment bars, but higher failure rates of bars where distal cantilever extensions were used. There were no explanations or descriptions of the nature of those failures in the clinical studies reviewed. The second search on fixed prosthodontic literature identified multiple factors that could potentially relate to the failed solder joints with bar attachments. Two potential sites of failure in bar attachments with distal cantilevers were identified, and a simple estimate of the tensile stresses at the solder joints was performed. The values found are comparable to the fatigue failure stresses reported in the searched literature.

Comparative tensile strengths of preceramic and postceramic solder connectors using high-palladium alloy

STATEMENT OF PROBLEM

It is not known whether different high-palladium alloys of similar composition possess comparable tensile strength properties associated with connector soldering.

PURPOSE

The purpose of this study was to evaluate the tensile strength properties of 2 high-palladium alloys on soldered connectors under simulated pre-ceramic and post-ceramic soldering conditions.

MATERIAL AND METHODS

Eighty cylindrical castings were fabricated (Rx Naturelle Plus alloy and Option alloy). The 40 castings for each alloy were subdivided into 2 groups of 20 each. In the first group, castings for each alloy were randomly paired and soldered with presolder (SMG2) to produce 10 preceramic test connector specimens for each alloy. In the second group, castings were similarly paired and soldered with postsolder (490 fine) to produce 10 postceramic test connector specimens for each alloy. Each soldered connector was subjected to tensile force until failure in a universal testing machine. Statistical analysis using a Wilcoxon rank sums test was performed (alpha=.05)

RESULTS

No significant difference was found between the mean tensile failure stress for Rx Naturelle Plus preceramic solder (344.7 +/- 77.6 MPa) compared to Option preceramic solder (411.5 +/- 112.8 MPa) (P =.1202). However, the mean tensile failure stress for Rx Naturelle Plus postceramic solder (260.8 +/- 223.7 MPa) was significantly lower than the Option postceramic solder (312.6 +/- 120.8 MPa) (P =.0407). Not only did Rx Naturelle Plus postceramic solder connectors show evidence of lower strength, but also an increased variation among specimens.

CONCLUSIONS

Rx Naturelle Plus solder connectors provided better strength with the preceramic as opposed with the postceramic connectors. For postsolder connectors, Rx Naturelle Plus alloy had less acceptable strength and a wider variation, suggesting it is more technique sensitive than Option alloy connectors.