I’m trying to make a model to use it with min3D on an android device.
Therefor I merged a human torso with an other head. To do this, I merged every vertex from the boundary of the head with a vertex from the torso. But this generated some faces without the dot in their center. But when I check the orientation of the normal of these faces, they are facing outwards. It also seems, that the faces without dots are round and not flat.
The problem is, that when I export the model to min3D the faces without dots get invisible.
Make some screenshot (zoomed into the problem area) in edit mode, face selection, at least. Upload pasteall.org, post link here. Sounds like you do not have any faces there at all, just edges.
You can merge selected edge loops using w - Bridge edge loops; no need to go by vertices. Select loop by Ctrl-Shift-RMB.
Faces ‘without’ dots are actually faces that have very bad geometry with the verts spread out and should be deleted if you can find them. They are usually caused by squidgy imports or by accidentally hitting the F key. ‘Remove internal’ should do for some of them, and ‘find nonmanifold’ should find some too.
Usually when this happens to me it’s faces underneath other faces. Ngons that connect verts that shouldn’t be connected. Just select all the odd areas and delete faces, then fill them in properly.