How do I fill the gap between groups of vertices for 3D printing? I have a 3D model which i want to 3D print, it has a face and a hair mesh which i initially joined to export a single PLY format mesh to 3D color printing. But then i noticed that the face and the hair (which both can be separated again easily so don't worry about that) have a gap between them, see:

More detailed view:



What i want to do is to extend the hair so it joins with the face. Is there a way to do that? Something like making new edges to join vertices of both groups of vertices?
like most things in computer science there's more than one solution 

One way would be to do it by hand. Just extend the thing and boolean it. 
The answer I prefer is to use meshmixer(free) and make solid the two objects. It looks something like this afterwards


Is that what the question was about ?