Common Dental Milling Issues EXPLAINED: Margin Chipping, Offset Lines, Chatter, Roughing Lines, Gouging, Equator Lines If you're seeing chipped margins, strange lines, or poor surface finishes on your zirconia crowns, this video is a must-watch. Rob Laizure from rebel3d and Greg Everett from Denteon walk through the most common dental milling problems—and how to fix them.