The retromolar pad is a stable, non-resorbing anatomical landmark located posterior to the mandibular molars. Covering this area with the denture base is essential to achieve a proper border seal, which helps in creating suction and retention of the lower denture. This seal prevents saliva and air from breaking the peripheral seal during function. Failure to include the retromolar pad may lead to poor retention and instability of the denture. Hence, the denture base must extend over the retromolar pad for an optimal seal and better denture performance.

Reference: Prosthodontics, Anil Chandra, 2nd Edition.