  We present a method enabling us to write in relativistic manner the wave
function of some particular two particle bound state models in quantum
mechanics. The idea is to expand the bound state wave function in terms of free
states and to introduce the potential energy of the bound system by mens of the
4-momentum of an additional constituent, supposed to represent in a global way
some hidden degrees of freedom. The procedure is applied to the solutions of
the Dirac equation with confining potentials which are used to describe the
quark antiquark bound states representing a given meson state.
