Standard Delaunay refinement works only for polyhedra with input
angles no more than 90 degrees. It was a challenge to extend it to
polyhedra with small input angles. Recently we designed an algorithm
to handle polyhedra with small input angles in the following paper.
S. W. Cheng, T. K. Dey, E. A. Ramos and T. Ray. Quality meshing for polyhedra with small angles. Proc. 20th Annu. Sympos. Computational Geometry, 2004, 290--299.
The QualMesh software based on this result is available.