Instrument used to plane buccoproximal and linguoproximal walls in class II cavity is:
Enamel hatchet
Bibeveled hatchet
Chisel
Single sided chisel
With the enamel hatchet or the bin-angle chisel or both, the dentist can cleave away any remaining undermined proximal enamel, establishing the proper direction to the mesiolingual and mesiofacial walls.