It probably is not burned out. When you get a coating of a foreign material (such as silicone) on the element, it shields the element from the alcohol so the alcohol can not support a catalytic reaction.

If you are the type that wants the last bit of use out of a plug, you can probably use it for bench running engines as long as you keep the booster connected in lieu of the catalytic reaction. This is handy since modern AB(X) engines throw off some metal particles at first which can partially foul a plug (taters). Save the good plugs for after this initial wear-in.

George