stl-sliver-hexa mesh
 

Dear all,
I have got a problem at meshing an stl geometry at the moment ( I took a glance at the other threads dealing with stl-file, but could't find a solution for my problem yet).
There are several bifuractions at my vessel geometry and slivers appear just in the middle of my bifurcation where the vessels meet, at the surface (see pic). My Ogrid hexa mesh has a good overall quality, but there are really bad and inverted elements at this slivers and close to them. Does anybody have an idea how to solve this?
I thought it might be better to solve this at the meshing process and not to smooth the surface itself. But is it possible to let ICEM ignore such surface disturbance when I want to generate an Ogrid hexa mesh? Maybe I did something wrong at trying it.
Thanks a million for any help and idea!
Lilly