Does tetrachlorodibenzo-p-dioxin (2,3,7,8) have a nonzero dipole moment? I've looked at and drawn the structure, and I originally felt that it would be nonpolar - as I believe all the dipoles would cancel out, but I'm not 100% sure. I might be too dependent on the fact that it looks symmetric.

Also, is it true that the overall molecule shape would be planar? And is the hybridization of the oxygen atoms sp3 like I think they are?

Edit: Thanks to a commenter, I have changed the question to ask about the dipole moment in hopes of being more clear. I'd also like to add that this is a homework question that I am stuck on (for general chemistry l) and the teacher hasn't been the most thorough which is why I am here trying to teach myself.
The best answer for this seems to be in Structure, Energy, Vibrational Frequencies, and Potential Energy Curve of
2,3,7,8-Tetrachlorinated Dibenzo-p-dioxin: Ab Initio MO Studies J. Phys. Chem., 1996, 100 (12), pp 4810–4814.  

This research finds that though planar is the lowest energy conformation, the energy for bending with respect to the O-O axis from 180 degrees to 170 degrees is only 0.008 kcal/mol.  The molecule flaps like a butterfly.  

The article says:  


  At ambient temperatures, nonplanar conformations
  will be significantly populated for this potential. This prediction
  accounts for the experimental results that the electric dipole
  moment of the DD molecules is reported to be 0.64 D. [reference 24]  


Where "DD" means the unsubstituted dioxin and where reference 24 is Higashi, K.; Uyeo, S. J. Chem. Soc. Jpn. 1941, 62, 396.