How is the posterior palatal seal (post dam) area of a complete maxillary denture determined?

The posterior palatal seal (post dam) is established at the vibrating line — the junction between the movable and immovable portions of the soft palate, also known as the AH line (anterior vibrating line) and PH line (posterior vibrating line). The patient is asked to say 'Ah' to identify the vibrating line, which marks the posterior extent of the denture and the location of the post dam. This seal maintains negative pressure to help retain the complete maxillary denture. The uvula is posterior to the post dam area. Tissue resilience influences seal depth. The tuberosity is a lateral border landmark, not the post dam location.