A question I periodically see on forums and discussions with WPF 3D graphics users is, "how do I draw wireframe" content for 3D. This isn't supported out of the box, but couple strategies I would suggest are:

• The out of band 3DTools library from members of the WPF 3D team includes "ScreenSpaceLines" which allows for wireframe rendering of lines.

http://www.codeplex.com/3DTools

•  Charles Petzold has also posted about wireframe rendering with his own implementation.

http://www.charlespetzold.com/blog/2007/08/310158.html