  We use molecular dynamics simulations to study coarsening dynamics in achiral
banana-shaped bent-core liquid crystals following a quench from the high
concentration polar smectic (SmX) phase to lower concentrations that favor the
exotic twist-bend (TB) phase. Our novel result is the identification of an
intermediate splay-bend state emerging prior to the eventual TB phase. The
latter coarsens via the annihilation of {\it beta lines} which are analogous to
string defects in nematic liquid crystals. Our findings are relevant for a
large class of chiral systems assembled from achiral entities.
