Edit 3D CAD model of tooth

I need someone good at editing with 3D models, I have the scan (A SAT file which came from a STL file extracted from DICOM images) of a tooth which will later be used for finite element analysis. At the beginning, we did not consider the roots of the molar to be important so they were left aside. Unfortunately, due to a change in the project I now need someone to add "roots" to the molar. It only has to be an approximation (not precise) I will include photos of how the roots need to be more or less. The file I have now is in a .SAT format. A plus would be if you can also change the SAT file to one that doesn't have a triangulated surface as this would make my work much easier later on. The whole tooth (part I have + the added roots) would be around 2 cm in total in height.