SOLDERING AND REMELTING INFLUENCE ON FATIGUE-STRENGTH OF COBALT-CHROMIUM ALLOYS

Statement of problem. For laboratory production, it would he economica lly advisable to reuse excess cobalt-chromium alloys in manufacturing partial denture frameworks. Furthermore, discrepancies in tit, modific ations, repairs, and also economic factors could lead to soldering pro cedure on the metal frameworks. Purpose. This study evaluated the infl uence 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 submitte d or not submitted to conventional soldering procedure. Material and m ethods. The soldering procedure was conducted in rod specimens 1.7 mm in diameter made with new, or with a mature 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 si mulating the insertion and the removal of partial dentures. After fail ure, the fracture surface was examined with a scanning electron micros cope. Results. The soldered specimens revealed 1119 loading cycles bef ore fracture. These means differed statistically from those of intact alloys, which disclosed 2733 cycles before failure (p < 0.05). Statist ical analysis indicated that the soldering procedure reduced fatigue s trength of all new alloys or those in a mixture of new and previously casted alloys. It was also found that the soldering procedure may caus e premature failure of a removable partial denture. Photomicrographs f rom fracture surfaces revealed the presence of inclusions and voids. C onversely, there n ere no significant differences between neu and reus ed specimens, soldered or not (p > 0.05), which suggested that it may be possible to reuse excess cobalt-chromium alloys without compromisin g the fatigue strength of the framework.