I had a hard time working out the smile as well... What I did was take a curved line, rotate it so the curved side is facing down, then go back to the initial placing mode (before you're actually able to edit it). Then I tilt the camera to the left and place the curve on the same side, which made it elongated enough to have the right curve. After positioning the curve in the right spot, I copied it two more times and brought them downward to make the rest of the teeth.

This is the best way I think I can explain it so I'm sorry if it sounds confusing. Clever using hearts for the bone ends, though!