I sculpted these lips based on several photo portraits I had collected. I had the idea while perusing 2D form guides and began each sculpt from a sphere to demonstrate the importance of a curving mass in both directions (vertically and horizontally). One of the toughest things about sculpting lips, to me, is getting the crease to cast just the right shadows. The limits of dynameshing often competed against that but I was more than satisfied with the results. I suspect that the SSS of a skin shader might make that particular challenge moot, though. Another challenge was to find an appealing point at which to end the faces. With the wrinkled lips, I had to include much more of the face to get a real impression of the form of the head in that region.
A second study was of a set of dentures that I could use and refer to repeatedly in the future. I was having trouble grasping the initial task of modeling a full set of teeth and felt overwhelmed by the particular forms of each tooth. Rather than wasting time modeling what I clearly didn't understand, I chose to sculpt a full set of teeth from scratch. I later retopologized the teeth as one piece and as individual teeth and created several additional mouth related pieces for the animators to choose from. They've proved handy several times already and are currently being used as the default teeth for the project I initially made them for.