What did I do wrong with the seams of my skull?

The is a top down view of the skull in the Unreal Developers Kit. I can’t get rid of these seams, does anybody know any techniques or videos that could help?

If you are sure that you used right axis directions while backing then use a higher ‘margin’ value.

Edit:
Seems will always be visible in one way or another so try to hide them, don’t put 3 of them on top of a skull.