Non-textured sculpt, rendered with the toon shader and made into a poster in Photoshop.
He was supposed to look more psychotic, but in the end he comes off looking borderline psycho/friendly, which is almost better.
In-Blender view and base mesh:
looks pretty nice - good sculpting work 
I think you might just need to angle his eyebrows down a bit to make him look scarier than he is already…
He haunts my dreams 
Kind of reminds me of V for Vendetta. The kids will never want to see the dentist’s office again after they see this 