The effects of recasting on the cytotoxicity of base metal alloys.
BACKGROUND
Cytotoxicity of cast alloys depends on their composition and element release, which may be affected by recasting of the alloy.


OBJECTIVE
This study investigated the effect of recasting on the element release and cytotoxicity of 5 base metal alloys.


METHODS
The alloys tested consisted of: 2 Ni-Cr (Remanium CS and Wiron 99); a Ni-Cr with Cu (CB Soft); a Co-Cr (Wirobond C); and a Cu-base (Thermobond). Alloy specimens (disks 3 x 5 mm) were cast as follows: 100% new alloy; 50% new with 50% recast; and 100% recast (n = 6). Cytotoxicity was tested using Balb/C 3T3 fibroblasts and the MTT assay. Six replicates were tested for each alloy, and the controls consisted of 6 wells containing cells with no alloy specimens. The release of elements from the alloys into culture medium was also investigated. The data were analyzed by 2-way analysis of variance (ANOVA) followed by the Tukey Honestly Significant Difference test (family error rate =.05).


RESULTS
At all 3 variations of casting, Remanium CS and Wiron 99 were the least cytotoxic, followed by Wirobond C, CB Soft, and Thermobond. ANOVA revealed significant differences between the groups (P <.001). Post hoc analysis showed that overall, Thermobond was significantly more cytotoxic than all of the other alloys tested (P <.05). For the 100% new alloy groups the cytotoxicity of Co-Cr alloy Wirobond C was similar to that of the Ni-Cr alloys Remanium CS and Wiron 99; however, when the alloys were recast, Wirobond C became significantly more cytotoxic and as toxic as the Ni-Cr alloy containing Cu (CB Soft). Moreover, recasting significantly increased the cytotoxicity of all the alloys (P <.05) and the amounts of elements released from them.


CONCLUSIONS
The Cu content in an alloy increased its cytotoxicity level remarkably. Recasting of alloys significantly increased their cytotoxicity level. The Co-Cr alloy was more adversely affected by the recasting than the Ni-Cr alloys.
Al-Hiyasat
Ahmad S
AS
Department of Restorative Dentistry, Jordan University of Science and Technology, Irbid 22110, Jordan. hiyasat@just.edu.jo
Darmani
Homa
H
D000818:Animals; D002857:Chromium / Q000633:toxicity; D003035:Cobalt / Q000633:toxicity; D003300:Copper / Q000633:toxicity; D003722:Dental Alloys / Q000737:chemistry / Q000633:toxicity*; D008422:Materials Testing; D051379:Mice; D008807:Mice, Inbred BALB C; D009532:Nickel / Q000633:toxicity; D018675:Toxicity Tests
D003722:Dental Alloys; D002857:Chromium; D003035:Cobalt; D003300:Copper; D009532:Nickel