  We explore the influence of heavy quarks on the deconfinement phase
transition in an effective model for gluons interacting with dynamical quarks
in color SU(3). With decreasing quark mass, the strength of the explicit
breaking of the Z(3) symmetry grows and the first-order transition ends in a
critical endpoint. The nature of the critical endpoint is examined by studying
the longitudinal and transverse fluctuations of the Polyakov loop, quantified
by the corresponding susceptibilities. The longitudinal susceptibility is
enhanced in the critical region, while the transverse susceptibility shows a
monotonic behavior across the transition point. We investigate the dependence
of the critical endpoint on the number of quark flavors at vanishing and finite
quark density. Finally we confront the model results with lattice calculations
and discuss a possible link between the hopping parameter and the quark mass.
