Adding a mouth-bag allows us to open and close a sculpted head.
Adding the mouth-bag
Start with the head loaded into zbrush. As you can see, this was sculpted with the mouth closed.
Disable all subtools except the one with the mouth on it.
Move into front view and disable perspective by pressing P
Append a Sphere3D
Select the new Sphere3D and enable transparency. Position the sphere as it is now the inside of your mouth.
Subdivide the sphere 2 times and then from the front view (still without perspective) make a mask tracing where the lips meet.
Your line should be thin clean and as smooth as you can make it.
Invert the mask, go into side view and press W to enter move mode
Move the unmasked area forward so that it goes through the lips
The geometry here is horrible so apply a ZRemesher.
Much smoother…
Go back to the Subtools Pallet and set the mouth shape to be subtractive.
Enable Live Boolean in the top left of the screen
Now our mouth is subtracted from the head. But they are still separate subtools and are not easy to work on later.
Select Boolean -> Make Boolean Mesh. This will create a new ZTool with a mesh made from the head with the mouth shape subtracted
Select ‘Append’ and choose that ztool.
Cleaning up the lips
We can now hide the original head and mouth subtools. You could delete the mouth subtool at this point but do NOT delete the original head yet.
Choose the ‘Select Lasso’ brush
Select the bottom jaw
Toggle which part is shown and which is hidden until the top and bottom lips are neatly separate.
Take care of the corners too…
While showing hiding each half, mask the whole lot and select ‘Group Masked’ in the Polygroups pallet
At this point, you should have 2 separate polygroups. Shift-Ctl clicking on either should make it the only one visible
To start cleaning up and finish shaping the lips, first we will dynamesh. If your lips come out stuck together, then increase the ‘Resolution’ slider
Enable symmetry and smooth out the each lip. Hiding the opposite polygroup makes accessing the lips easy
Smooth out the opposite lip
Now we have lips, let’s close them…
By hiding one polygroup, we can mask a single lip
Do this for each lip until the lips meet as you want them to
Remove the masks and smooth the corners
Fixing topology and getting details back
Now is time to get some nicer topology and get our detail back. Use Zremesher to make a nice pretty mesh. Make sure to select ‘KeepGroups’ we still need the separate group for the jaw so that we can open the mouth.
The result is a low poly mesh that matches the curves of our sculpt
Now, to get our detail back… Go to the subtool palette and make the original head visible. The only two tools visible should be the original head and our new head.
Press Ctr-D to subdivide the mesh, then go to Project -> Project all to project the detail back on to our new mesh. Do this a few times until you have the resolution you require.
Now we have a nice, detailed, high poly mesh with lower subdivisions and a neat polygroup for the bottom jaw.
There is a small issue on the lips where there was a difference between the new and old mesh. A single stroke with smooth should clear it up instantly. I forgot to do this and did it at a later step but it’s probably best to do it now. Now is a good time to save a backup of your ztool.
Opening the mouth
In the Layers Pallet, click the new layer button. The new layer is added and automatically in record mode
Move down to a lower resolution subdivision
Mask the bottom jaw (with the help of your polygroup) and blur the mask quite a bit.
Invert the mask, enter move mode and move the gizmo so that it’s at the pivot point of the jaw.
Pivot the Jaw so that it’s open
Shape your lips how you want them when open
Adjust the masseter shape to deform properly when open
Adjust the shape of the facial muscles to react to the jaw opening. Feel your own face or look in a mirror if you need help understanding how it reacts
Go back up to the highest subdivision level.
Blending facial expressions
Now if we go back to the layers pallet, we can control how much the jaw is open or closed
Add a new layer for each facial expression and sculpt the face to match that expression
You can now mix these different layers or expressions to get whatever combination you want