  The link between dynamical chiral symmetry breaking and centre vortices in
the gauge fields of pure $\mathrm{SU}(3)$ gauge theory is studied using the
overlap-fermion quark propagator in Lattice QCD. Overlap fermions provide a
lattice realisation of chiral symmetry and consequently offer a unique
opportunity to explore the interplay of centre vortices, instantons and
dynamical mass generation. Simulations are performed on gauge fields featuring
the removal of centre vortices, identified through gauge transformations
maximising the center of the gauge group. In contrast to previous results using
the staggered-fermion action, the overlap-fermion results illustrate a loss of
dynamical chiral symmetry breaking coincident with vortex removal. This result
is linked to the overlap-fermion's sensitivity to the subtle manner in which
instanton degrees of freedom are compromised through the process of centre
vortex removal. Backgrounds consisting solely of the identified centre vortices
are also investigated. After smoothing the vortex-only gauge fields, we observe
dynamical mass generation on the vortex-only backgrounds consistent within
errors with the original gauge-field ensemble following the same smoothing.
Through visualizations of the instanton-like degrees of freedom in the various
gauge-field ensembles, we find evidence of a link between the centre vortex and
instanton structure of the vacuum. While vortex removal destabilizes
instanton-like objects under ${\cal
  O}(a^4)$-improved cooling, vortex-only backgrounds provide gauge-field
degrees of freedom sufficient to create instantons upon cooling.
