Why are there no edge dislocations in a face-centered cubic (FCC) lattice?
I have to stretch my memory to remember how this goes (and read a bit from here).

First, how do you define burgers vector? You take the end point of the dislocation and make a circle around it as it were a perfect lattice, the extra (or missing step) from the full loop is the burgers vector. 

Now, is the burgers vector also a lattice vector? If yes, then it is (edge)dislocation. If no, then it is only a partial (edge)dislocation (partial dislocations have their own name). 

Now, how does this work on a fcc-lattice case. On quick read for link I pasted, it seems that fcc-lattice cannot have edge dislocations, because the burgers vector is not a lattice vector.

You may want to go this through by yourself and check that I didn't make any mistakes.