By setting maxHeight="Infinity" or maxWidth="Infinity" attributes on a button, you can allow a button to expand to fill it's available width (e.g. completely fill a tile in a tile pane.)

It would be nice to have updated fxml documentation (http://download.oracle.com/javafx/2.0/api/javafx/fxml/doc-files/introduction_to_fxml.html) to reference these settings.

Refer to forum thread: https://forums.oracle.com/forums/thread.jspa?threadID=2307430&tstart=0 for context.