First off, when you use dynamesh it is often beneficial to have the “project” and “polish” options selected within the dynamesh options panel. It will take a little longer to remesh, but you’ll get better results.
Every once in a while dynamesh seems to do that thing with the holes. Not sure why, but no amount of noodling the settings will correct it. (at least in my experience.) What I’ve done in the past is try to fool the system. I will start with a new polymesh object (like the star) and then append the sacked-out subtool and try to remesh again in that new scene. You can also try exporting the subtool as a .obj file and then re-import and try remeshing again. If that doesn’t work you can also try to change that .obj slightly in the 3d application of your choice. (In maya you might “smooth” it to add a lot more polygons. Then re-import that obj back into Zbrush and try again. When you make changes like that the program needs to re-write the file and it may get rid of any corruption.
I also make it a habit of repeatedly saving new copies of my ztool every half hour so that I have a stable copy in case something goes bad. That way you can just open the old file and append the specific subtool to your new file. You can then delete the corrupted subtool that was giving you trouble.
I know this sounds like a lot to throw at you if you are new to the program. Don’t hesitate to ask for clarification on any of these points if it comes across like Greek.
I remember I got these kind of holes on very thin parts of the mesh. So maybe what could help if you use a large move topological brush to move away one side of the surface from the other. normal brushes probably wont work because they move both sides at once.
You have thin mesh, and dynamesh doesn’t work well with thin mesh. What i will do is use turn on BackFaceM, then use the ClayBuildUp to scrulpt that area and use smooth brush to relax it. When it’s done, apply the dynamesh again.
I’m not sure what a “thin mesh” is since all 3D is just surface geometry. Do you mean that the mesh isn’t dense there? If so, he could also just mask the entire model and do a really thin mesh extraction. That would create new topology anyway and it may set it up better for future dynamesh on the subtool.
“Thin” not like “low polygon density”, but like “low mesh thickness”, such as cloth has.
When the front and the backside nearly touch each other, dynamesh gets into problems, so one of the sides has to be moved away from the other. Using backsidemask like encore said look like a good option for doing that.
Back face works well, also thanks everyone coming to my rescue