  We present the formalism for a new generation of unquenched quark models in
which quark-antiquark pair effects are taken into account in an explicit form
via a microscopic QCD-inspired quark-antiquark creation mechanism. No
truncation in the sum over all the big tower of states is necessary since these
states are automatically generated by means of powerful group-theoretical
techniques. An important check on the formalism and the numerical results is
provided by the closure limit. As an application, the effect of quark-antiquark
pairs on the strange content of the proton spin, $\Delta s$, is discussed. The
contributions of the up and down quarks, $\Delta u$ and $\Delta d$, are also
calculated. This has become possible after solving the difficult problem of
permutational symmetry related to quark rearrangements. Finally, we present
some preliminary results in the closure limit as well as an outlook for future
applications.
