  We derive new explicit expressions for the Dirac bilinears based on a generic
representation of the massive Dirac spinors with canonical polarization. These
bilinears depend on a direction $n$ in Minkowski space which specifies the form
of dynamics. We argue that such a dependence is unavoidable in a relativistic
theory with spin, since it originates from Wigner rotation effects. Contrary to
most of the expressions found in the literature, our ones are valid for all
momenta and canonical polarizations of the spinors. As a by-product, we also
obtain a generic explicit expression for the covariant spin vector.
