"Babyteeth" is a debut feature from Australia, and what a debut: Shannon Murphy, who's never done a full-length film before, directed from a screenplay by Rita Kalnejais. The genre is familiar, a lovely young girl with a disease that may kill her, but that's where the familiarity ends and a wonderfully unpredictable tragicomedy begins. The girl, Milla, is played by Eliza Scanlen, who was so radiant as Beth in Greta Gerwig's "Little Women." Toby Wallace is remarkable as Moses, the whacked-out love of Milla's life.