Freehand superimpositions on bony structures, as suggested by Dr. Björk and others, can now be accomplished easily using Apple's Quartz framework. X-rays can be manipulated and superimposed transparently on screen. This feature is also useful for superimpositions that are required by the ABO.
To perform the freehand superimposition, you simply make a new Comparison from the Session menu, select the superimpositions section, then turn on the view of the x-rays you wish to superimpose.
You can turn off the tracings to view the superimposition easier. You can also change the axis of rotation for the superimposition, so if you wanted to rotate about a particular landmark, you can easily do so.