The effect of nickel as product of recasting nickel chromium on gingival fibroblasts apoptosis

NiCr restoration recasting causes an increase of Ni solubility in artificial saliva. Nickel [II] can freely enter the cell and behaves as a free radical causing oxidative stress and inducing apoptosis. The purpose of this study was to determine the highest [Ni] in the artificial saliva and its effect on apoptosis of gingival fibroblasts. Three types of NiCr restoration are prepared (casting ; one-time recasting and two-times recasting). Each restoration consisted of 8 speciments, and was subsequently immersed in artificial saliva for 7 days. The highest [Ni] in each restoration was exposed to the gingival fibroblasts culture with a density of 10⁵, and incubated for 1, 3, and 7 days. Analysis of [Ni] was performed by AAS, whereas apoptosis was determined by the used TUNEL assay method. The highest [Ni] on restoration casting was 0.780 μg/L; while one-time recasting was 3.002 μg/L, and two-times recasting was 6,320 μg/L. There was an interaction between increased Ni solubility and exposure duration to apoptosis of gingival fibroblasts (p< 0.0001). The greatest mean ± SD of apoptosis was on the exposure of 6,320 μg/L with an incubation period of seven days ( 62.13 ± 2.85 ). It can be concluded that the higher [Ni] is exposed to gingival fibroblasts in cell culture, the higher the incidence of apoptosis. Nickel [II] suspectedly enters into the cell via DMT - 1, which subsequently triggers apoptosis characterized by ROS generation and reduction of Bcl-2 expression.