when your 18's came off, were you using the correct type of lug nuts? stock domed ones dont work on most aftermarket wheels.

in any case, I usually drive my car around for a few miles, and torque them again when i get back. Then a week or two later ill check the torque on them.

when you torque them, go in a criss cross pattern, and go around twice. Torque 4, and then start again from the 1st and go around again. Sometimes torquing down the other 3 will leave the first one w/ some thread to go.