What is the most common cause of gagging in a patient wearing a complete maxillary denture?

The most common cause of gagging with a complete maxillary denture is overextension of the posterior palatal seal (post-dam region). When the denture base extends too far posteriorly, it contacts the soft palate and triggers the gag reflex by stimulating sensory receptors. The posterior palatal seal should end just anterior to the vibrating line at the junction of the hard and soft palate. Mandibular denture extension and VDO issues can also cause discomfort but are less commonly the cause of gagging.