  The widely accepted dark matter hypothesis offers a seductive solution to
missing mass problems (galaxies, clusters of galaxies, gravitational collapse
in structure formation,...). However the physical nature of the Dark Matter
itself is still unknown. Alternatively, it has been proposed that apparent
dynamical evidence of dark matter is due to a modification of Newtons's law of
gravitation. Here we revisit the Modified Newtonian Dynamics (MOND) theories at
the scale of galaxy clusters. Using hydrodynamical simulations, we derived
quantities such as the density and the temperature of the ICM. We compared
those MOND simulated predictions to high quality X-ray density and temperature
profiles observed down to ~0.5 the virial radius. If the density profiles seems
in acceptable agreement, the simulated temperature show a constant increase
with the radius whereas the observed profiles show a flat to a mild decrease
shape down to ~0.5 Rvirial . We also computed the dynamical MOND mass for 8
X-ray clusters observed with XMM-Newton. If the MOND mass helps to lower the
discrepancy with the baryonic mass by ~20%, still ~80% of the mass in clusters
is unaccounted by baryons. In order to solve this problem and to reconcile MOND
with clusters observations, we investigated the possibility of an added dark
baryonic component. We assumed a component of massive neutrinos to fill the
remaining discrepancy between the observed MOND dynamical mass and the baryonic
mass. This led us to derive a tied observational lower limit for the neutrino
mass, m_nu > 1.06 eV.
