  We study collisional rethermalization in ultracold dipolar thermal gases,
made intricate by their anisotropic differential cross sections. Theoretical
methods are provided to derive the number of collisions per rethermalization,
which for dipolar gases, is highly dependent on the dipole alignment axis.
These methods are formulated to be easily applied in experimental contexts,
even reducing to analytic expressions if the route to thermal equilibrium is
governed by short-time dynamics. In the analytic case, collisional
rethermalization is fully characterized by the dipole magnitude and
orientation, scattering length, and thermalization geometry. These models
compare favorably to Monte Carlo simulations, and are shown to model well a
recent experimental result on the rethermalization of polar molecular samples.
