Your 3D model’s edges are hidden typically due to viewport settings, layer visibility, or rendering preferences that turn off edge display.
Viewport modes like "Shaded" hide edges by default to emphasize surface details over lines. If the edge layer is toggled off or invisible, edges won’t appear. Some real-time renderers disable edges for better performance or a cleaner look.
Try switching to "Wireframe" or "Edges on Shaded" mode, checking edge layer visibility, or using your software’s view menu to toggle edges—most 3D tools have a quick setting for this.