Which palatal vault form provides the BEST retention for a maxillary complete denture?

Correct answer: A. A broad, gently curved U-shaped vault

• A. CORRECT. A broad, moderately deep U-SHAPED vault is ideal. It provides a large surface area for adhesion and cohesion, its walls are close to perpendicular to the path of dislodging forces so they resist lateral movement, and the tissue is uniformly displaceable, which allows a reliable peripheral and posterior palatal seal.
• B. A prominent torus palatinus requires relief or surgical reduction; left untreated it causes the denture to rock about the fulcrum of the torus and destroys the seal.
• C. A narrow, high V-SHAPED vault is the worst form. The steep walls mean any lateral force breaks the seal immediately, and the sharp midline crest is easily traumatised. These patients need meticulous impression technique and often accept reduced retention.
• D. A flat vault offers surface area but almost no resistance to lateral displacement, so the denture slides readily.

Note: Retention comes from an accurate, intimate fit with a thin film of saliva (adhesion, cohesion, interfacial surface tension) plus atmospheric pressure behind a complete border seal. Stability and support come from ridge form and the denture-bearing area. A U-shaped vault serves all three.