Initial versus subsequent release of elements from dental casting alloys.

The release of elements from dental casting alloys is directly related to adverse biological effects they may have. Longer-term (>1 month) studies of elemental release have suggested that release decreases significantly after a higher initial release of elements. The aim of the current study was to measure the release of elements from a variety of clinically relevant dental casting alloys and compare the release at weekly intervals through 4 weeks. The hypothesis was that the release during the initial week should be higher than in subsequent weeks, and that cytotoxicity should decrease as elemental release decreases. Alloy samples were exposed to cell-culture medium which was changed at weekly intervals and assessed for elemental release by means of atomic absorption spectrometry. The cytotoxicity of the medium was also measured. The results showed that for single phase alloys, initial release was often significantly higher in the first weeks than in subsequent weeks, but not for all elements in an alloy. Multiple phase alloys showed steady or increasing release relative to the first week. Cytotoxicity relationships were complex depending on which elements were released and the ratios of elements released. This study suggests that short-term tests (<1 week) may not be appropriate to evaluate longer-term elemental release or cytotoxicity because of changing rates of elemental release.