  In recent years, the discovery in quarkonium spectrum of several states not
predicted by the naive quark model has awakened a lot of interest. A possible
description of such states requires the enlargement of the quark model by
introducing quark-antiquark pair creation or continuum coupling effects. The
unquenching of the quark models is a way to take these new components into
account. In the spirit of the Cornell Model, this is usually done by coupling
perturbatively a quark-antiquark state with definite quantum numbers to the
meson-meson channel with closest threshold.
  In this work we present a method to coupled quark-antiquark states with
meson-meson channels, taking into account effectively the non-perturbative
coupling to all quark-antiquark states with the same quantum numbers. The
method will be applied to the study of the X(3872) resonance and a comparison
with the perturbative calculation will be performed.
