Ideally In a finite element analysis we are trying to find out the maximum strain generated with a perticular amount of load. an von miss analysis gives a combination of all the stresses generated.Hence you can see most of the studies published show only the von mises analysis.
I do agree with Ramesh Chowdhary : on top of this, we need to consider Maximum and Minimum principal stresses because it is know that bone is very good in with standing high compressive stress. This in-turn depend on many factors the shape of implant thread and other geometrical factors and was well as stability of bone- implant contact (BIC). Also we need to consider maximum microStrain to see its intensity in causing bone resorption around crestal module of compact bone. Hence not only Von mises but also those parameters to infer final decision before clinical testing.