Final answer:
The retromolar pad is the landmark used to determine the height of the occlusal plane for posterior teeth in a mandibular complete denture.
Step-by-step explanation:
The landmark used to determine the height of the occlusal plane of the posterior teeth in a mandibular complete denture is the retromolar pad. It is considered as a stable and reliable anatomical reference point for establishing the occlusal plane in denture construction. The retromolar pad is a small area of dense, fibrous tissue located just distal to the last standing molar on the mandibular arch, providing a significant reference for the arrangement of mandibular posterior teeth.