A complete denture patient complains that the lower denture tips when biting. What is the most likely cause?

When a complete mandibular denture tips or rocks during function, the most common cause is overextension of the posterior (distal) flanges. An overextended posterior border of the mandibular denture contacts the retromylohyoid space or buccal shelf during function, causing the denture to unseat anteriorly (tipping/rocking). The ideal answer would be overextension of the posterior palatal seal (PPS) area, but among the given options, distal extension is the closest correct answer.