At re-entrant corners you need to provide for the restrained shrinkage and early age thermal effects at the corner. You also need to detail for proper anchorage of reinforcement. In a thin slab (up to about 20 cm), two layers of 2 bars of the same size as your orthogonal reinforcement, but not less than 12mm should be used.
For thicker slabs, mid level corner bars are also needed.