Corrosion resistance of solder joints for removable partial dentures

The corrosion resistance of different alloy-solder combinations commonly used for removable partial dentures was evaluated, employing partial denture frameworks fabricated using standard laboratory procedures in order to reproduce the real situations. Specimens of 6 partial denture alloys (4 non-precious and 2 precious ones) were soldered in several combinations and placed in Ringer's solution at 37°C. After 30 days of immersion the samples were examined for evidence of corrosion by optical and scanning electron microscopy. The results indicate that the performance of a solder joint in an aggressive medium can be adversely affected by overheating, which may cause the formation of voids and the sensitization to intergranular corrosion of stainless steel attachments, and by coupling alloys of different nobility, thus creating a galvanic cell and increasing the corrosion rate of the least noble alloy. Dramatic corrosion phenomena have been observed on the stainless steel attachments welded with gold solders. Good corrosion resistance is shown by cobalt-chromium devices; however, corrosion signs have also been in evidence on these alloys when they are coupled with gold alloys.