Great to see you got it up and running and it's looking good so far! May I suggest you begin your base mesh with zspheres, it would be alot easier to pull out the mandibles that way and you'll have more resolution there. I have here a suggestion/example. Hope this helps!
Well I never start a project straight from Zbrush, I always make low poly models in Maya then export them to zbrush for detailing. So if you have another 3D program you could very easily make a dread shape and export it.