if you know enough about electron microscopy to ask if you should take a course in it, then you already know enough about it to do well in dental school. Generally, the only time electon micrographs are shown are occasionally in basic science classes, and in restorative courses when they want to make a point about the microstructure of the tooth, to compare and contrast various cutting techniques/instruments, and to graphically describe assorted restorative materials.
The only reason I can think of to take e.m. is if you are planning on going into or doing some materials research.
Cheers!