  The relative contributions of explicit and dynamical chiral symmetry breaking
in QCD models of the quark-gap equation are studied in dependence of frequently
employed ans\"atze for the dressed interaction and quark-gluon vertex. The
explicit symmetry breaking contributions are defined by a constituent-quark
sigma term whereas the combined effects of explicit and dynamical symmetry
breaking are described by a Euclidean constituent-mass solution. We extend this
study of the gap equation to a quark-gluon vertex beyond the Abelian
approximation complemented with numerical gluon- and ghost-dressing functions
from lattice QCD. We find that the ratio of the sigma term over the Euclidean
mass is largely independent of nonperturbative interaction and vertex models
for current-quark masses, $m_{u,d}(\mu) \leq m(\mu) \leq m_b(\mu)$, and equal
contributions of explicit and dynamical chiral symmetry breaking occur at
$m(\mu) \approx 400$~MeV. For massive solutions of the gap equation with
lattice propagators this value decreases to about 200~MeV.
