  Scalar tetraquark states are studied within the diquark-antidiquark picture
in a non-relativistic approach. We consider two types of confining potentials,
a quadratic and a linear one, to which we also add spin-spin, isospin-isospin,
and spin-isospin interactions. We calculate the masses of the scalar diquarks
and of the ground-state open and hidden charmed and bottom scalar tetraquarks.
Our results indicate that the scalar resonances $D_{0}^{\ast}(2400)$ and
$D_{s}(2632)$ have a sizable tetraquark amount in their wave function, while,
on the other hand, it turns out that the scalar states $D_{s0}^{\ast}(2317)$
and $X(3915)$ should not be considered as being predominantly
diquark-antidiquark bound states. We also investigate the masses of light
scalar diquarks and tetraquarks, which are comparable to the measured masses of
the light scalar mesons.
