Nimi,
I know that majority (if not all) of Endodontics Post-doctoral dental training requires the GRE. To me, I think it's BUL# Shi@!! So, let me understand this, for a typical U.S. dental students, you've taken the DAT, NBDE Part I, NBDE Part II, and your regional licensure exam (or your state licensure exam), now you have to take the Graduate Record Examination (GRE) if you want to go into Endo!? Maybe since the Endo. specialty is so competitive that dental schools want it to make it MORE competitive by adding a "BS" examination in there (one more step that you'll have to take to apply).
At any rate, to answer you questions, yes, GRE is important in "some" post-doctoral dental training (for example: Endodontics). I'm not sure about Ortho, Pedo, Perio, or Prostho if GRE is needed. I know for sure that Oral Surgery, Advanced Education General Dentistry (AEGD), and General Practice Residency (GPR), the GRE is NOT required!
GRE studying materials, there are so many!!! I would recommend Kaplan, all their studying courses and printing materials are usually pretty good. I provided you with their web site:
<a href="http://www.kaptest.com/repository/templates/Lev3InitDroplet.jhtml?_lev3Parent=/www/KapTest/docs/repository/content/Graduate/GRE" target="_blank">http://www.kaptest.com/repository/templates/Lev3InitDroplet.jhtml?_lev3Parent=/www/KapTest/docs/repository/content/Graduate/GRE</a>
For the official GRE web site, visit:
<a href="http://www.gre.org/" target="_blank">http://www.gre.org/</a>
Good luck!