Which factor contributes MOST to the retention of a maxillary complete denture?

Correct answer: C. Intimate tissue adaptation with a complete and continuous peripheral seal

• A. Excessive base thickness adds weight — which works AGAINST maxillary retention, since gravity pulls the upper denture down — and encroaches on tongue and cheek space.
• B. The number of posterior teeth affects masticatory efficiency and load distribution, not the physical retention of the base.
• C. CORRECT. RETENTION — resistance to vertical dislodging forces — depends on the physical forces generated by a thin film of saliva between two closely adapted surfaces: ADHESION, COHESION, surface tension and, critically, atmospheric pressure maintained by an intact PERIPHERAL SEAL. If the border seal is broken anywhere along its circumference, air enters, the film breaks, and retention is lost regardless of how well the rest of the denture fits. Maximum extension within the functional limits of the moving tissues maximizes the surface area over which these forces act.
• D. Relief areas are provided to avoid pressure on non-resilient structures such as a torus. They are necessary for comfort but do not generate retention; a relief that is too large actually breaks the seal.

Note: Distinguish the three: RETENTION resists vertical displacement (peripheral seal, adaptation). STABILITY resists horizontal and rotational forces (ridge form, tooth position, occlusion). SUPPORT resists vertical seating forces (denture-bearing area, primarily the horizontal hard palate).