[In vitro metal dissolution under various extraction conditions].

Dissolution of components from pure Ni, pure Ti, NiTi alloy and 316 L stainless steel was examined in Eagle's minimum essential medium to evaluate the effects of dynamic condition, pH, extraction period and filtration on the corrosion behaviour. Extraction medium was pH 3.5, 7.0 and 9.5. Extraction was done under static and gyrating conditions of 160 rpm, 200 rpm and 230 rpm for 3 and 7 days. Under static conditions, nickel was eluted from pure Ni and NiTi alloy at pH 3.5. Nickel and iron were slightly eluted from 316 L stainless steel at pH 3.5. However, dissolution of components from alloys was greater under dynamic conditions and with longer extraction periods. Dissolution of components, particularly of nickel at pH 3.5, was the highest from pure Ni, NiTi alloy and 316 L stainless steel. Following filtration with a 0.22 micron filter, the amount of metal decreased. Titanium was not detected in the filtrate under the conditions tested. The finding that a considerable amount of nickel was detected in the extract and filtrate indicated that the element was present in both a soluble and particulate form, especially at pH 3.5. The present results demonstrate that extraction under dynamic conditions is useful for investigating the degradation of metallic materials for medical and dental use.