Mr Light wrote:
Maybe the worker was Russian and they used real metal teeth?
Well I'm pretty sure they specifically said "filling" but even if they didn't, do the Russians use iron, nickel, or cobalt for dental work? Maybe they do, I honestly don't know.
I think the more likely scenario is that it was just an "oops" on the part of the writers since somebody being killed by having a magnet suck a filling through his head seemed "cool."