On steel or aluminum, a dent is a multi-axis bend in the metal where the force applied exceeded the yield strength, but not its tensile modulus.

Because it's a yield failure, changing the temperature of the metal will not do anything, except make you look foolish. It can, however, be bent back without reducing the strength of the metal, hence a qualified dent repair person could make a repair.

Save your $5.00 on Duster and spend it later on real dent repair.