Creating Smiles

Roughly select the area around the mouth with the Polygon Lasso tool. Go to Select → Modify → Feather, and enter a radius of 10 pixels. Confirm, then click on Layer → New → Layer via Copy (or press Control/Command + J), then Edit → Puppet Warp. Photoshop will put a mesh over the entire layer in the shape of your previous selection.

                                                     Here’s the mesh over the layer.
 
You can control the size of the mesh with the “Expansion” value in the Options bar. Increase the density to “More Points” for increased precision. Press Control/Command + H to hide the mesh, then set the first pins to the corners of the mouth. Add more pins to distinctive spots of the mouth. By clicking and dragging the mesh, you can shape a nice smile.