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

Abstract

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. (J Prosthet Dent 1997;78:146-52.)