Compare chin bone orientation between the pre-operative planning and post operative result

How can i measure the yaw, pitch and roll for bone advancement of the chin to compare between the pre-operative planning and post-operative result ( material provided is in form of STL

You can register the bones in the two positions (using “fiducial registration”, optionally followed by surface-based automatic “Model registration”) and then you can get information about the rotation component of the transform using “Characterize transform matrix” module (in Sandbox extension).

I am not able to find the Slicersandbox extension . how can I download it

You can install the Slicer Sandbox extension from within Slicer using the Extensions Manager: