The tensile strength and appearance of solder joints in three base metal alloys made with high- and low-temperature solders

Soldering and remelting influence on fatigue strength of cobalt-chromium alloys

STATEMENT OF PROBLEM

For laboratory production, it would be economically advisable to reuse excess cobalt-chromium alloys in manufacturing partial denture frameworks. Furthermore, discrepancies in fit, modifications, repairs, and also economic factors could lead to soldering procedure on the metal framework.

PURPOSE

This study evaluated the influence of soldering and remelting procedures on the fatigue strength of Steldent, Dentorium, and Biosil cobalt-chromium alloys, as new alloys and in a mixture of new and previously casted alloy and when submitted or not submitted to conventional soldering procedure.

MATERIAL AND METHODS

The soldering procedure was conducted in rod specimens 1.7 mm in diameter made with new, or with a mixture of new and reused alloy (n = 10 per group). The results were compared with those of intact rods. The fatigue strength was carried out with a cyclic testing machine simulating the insertion and the removal of partial dentures. After failure, the fracture surface was examined with a scanning electron microscope.

RESULTS

The soldered specimens revealed 1119 loading cycles before fracture. These means differed statistically from those of intact alloys, which disclosed 2733 cycles before failure (p < 0.05). Statistical analysis indicated that the soldering procedure reduced fatigue strength of all new alloys or those in a mixture of new and previously casted alloys. It was also found that the soldering procedure may cause premature failure of a removable partial denture. Photomicrographs from fracture surfaces revealed the presence of inclusions and voids. Conversely, there were no significant differences between new and reused specimens, soldered or not (p > 0.05), which suggested that it may be possible to reuse excess cobalt-chromium alloys without compromising the fatigue strength of the framework.

Evaluation of soldered connectors of two base metal ceramic alloys

Soldered connectors for two base metal ceramic alloys (nickel-chromium and cobalt-chromium) were compared by use of four different techniques: (1) infrared preceramic soldering, (2) gas and oxygen preceramic soldering, (3) porcelain furnace postsoldering under vacuum, and (4) porcelain furnace postsoldering without vacuum. A control group was established with solid cast specimens of each alloy. No statistically significant difference was noted between infrared and torch preceramic soldering techniques for either of the two alloys. However, the joints postsoldered under vacuum were significantly superior to postsoldered connectors without vacuum (p < 0.0001). No significant differences were observed among techniques 1, 2, and 3, although the three groups were substantially superior to technique 4 for both alloys (p = 0.05). The control group for both alloys was appreciably stronger than the soldered groups (p < 0.0001), and the nickel-chromium samples within the control group were significantly stronger than the Co-Cr samples.

Repair of an overcontoured cemented crown

A method for retracting gingival tissue to allow recontouring of crown surfaces and removal of overhanging margins has been presented.

Tensile strength analysis of midpontic soldering

A total of 120 three-unit fixed partial dentures were made by using a latex mold to produce uniform wax patterns. Four groups were used to compare the tensile strength of connectors with interproximal solder, midpontic vertical solder, midpontic diagonal solder, and a control of one-piece castings. Three different metals were tested and the tensile load required to fracture the samples as well as the fracture sites were recorded. The following was found: Soldering the interproximal connector area produced the weakest solder joints, regardless of metal tested, at p less than .001. There was no significant difference in the fracture loads between midpontic vertical soldering and midpontic diagonal soldering with all three metals at p less than .01. There was no significant difference in fracture loads between midpontic soldering and unit casting with all three metals at p less than .01. The extreme variations in fracture loads when soldering nickel-chrome-beryllium confirms the technique sensitivity of presoldering this alloy.

Strength properties of soldered joints for a gold-palladium alloy and a palladium alloy

Strength of a soldered palladium alloy, PGC (Engelhard Corp.), and a soldered medium gold alloy, PGX (Engelhard Corp.), was examined. The results obtained were as follows: Highest strength was observed with postsoldered specimens of PGC alloy. Microstructural examination of postsoldered specimens revealed nearly pore-free solder joints with PGC and PGX alloys, and fracture appeared at the solder-alloy interface with PGC and PGX alloys. Microstructural examination of presoldered and presoldered/thermocycled specimens revealed that presoldered specimens of PGC and PGX alloys exhibited intrasolder fracture; PGX solder joints had considerably less porosity, which may explain the equivalent bond strengths of all the soldered specimens and the yield point of the controls; PGC solder joints exhibited large quantities of pores, which may explain the lower strength; pores observed in PGC alloy may be the result of the high fusing temperature of the solder; and these results indicate a need to develop a new presolder for PGC. The best result was obtained with postsoldered specimens of the PGC alloy. However, for PGX alloy, either postsolder or presolder techniques can be used.

Report on base metal alloys for crown and bridge applications: benefits and risks. Council on Dental Materials, Instruments, and Equipment

Despite the widespread use of nickel-based alloys, claims for the safety of these alloys have not yet been accepted universally. The allergenic effects of nickel on dental patients and the potential toxic effects of nickel and beryllium on laboratory technicians continue to cause concern within the dental profession. The systemic response to metallic nickel and nickel compounds as a result of intraoral corrosion and dissolution of nickel-based restorations over extended periods have not been studied adequately. The dental profession may be overgeneralizing the relative safety of nickel alloys because of the lack of allergy-induced intraoral lesions observed in private practices. Additional animal studies are needed to characterize the acute and chronic toxicities of nickel compounds. The potential for dermatologic and systemic effects that may occur in patients and dental personnel because of exposure to cobalt alloys must not be overlooked. Although sensitivity reactions may be of some concern, the toxicity potential of cobalt-chromium alloys appears to be insignificant. Little research has been done to determine the carcinogenic potential of nickel in dental laboratory technicians. In addition, animal and human studies are needed to determine the effect of nickel and beryllium exposure on the reproductive system. In the interim, specific equipment and facilities that minimize dust and vapor exposure to dental technicians should be identified to reduce airborne concentrations of nickel and beryllium in commercial dental laboratories to levels well below those established by the Occupational Health and Safety Administration.(ABSTRACT TRUNCATED AT 250 WORDS)