Wouldn't the Joker's Scars in Dark Knight make it impossible for him to smile?

hmmm As far as i know, even if he damaged his facial muscles, it wouldnt be such a big problem. Because even if muscles are damaged they can regenerate because of the presence of primitive muscle cells called satellite cells that can mature to form muscle fibers. So as long as he didnt keep cutting himself and wasting satellite cells, his muscles would regenerate and form fibers after 15 days...so im guessing it wouldnt take that much longer to regain function.