Which residual ridge and palatal form is MOST favourable for the RETENTION of a maxillary complete denture?

Correct answer: A. A well-defined, deep buccal vestibule with a high, U-shaped palatal vault

• A. CORRECT. Retention is generated by the border seal and by the physical forces of adhesion, cohesion and atmospheric pressure across the denture-bearing area. A DEEP, well-defined buccal vestibule allows a properly extended, well-adapted flange and therefore a competent peripheral seal, while a HIGH U-shaped vault increases the surface area available and — more importantly — provides vertical walls that resist LATERAL displacement. The combination is the classic ideal.
• B. A high vault helps with stability against lateral force, but without vestibular depth the peripheral seal cannot be established, and retention fails first.
• C. A deep vestibule permits a seal, but a FLAT palate offers no resistance to lateral displacement, so the denture slides under function even if it initially feels retentive.
• D. This is the least favourable combination on both counts: no vestibular depth for the seal and no vertical form to resist lateral force.

Note: Both are favourable and the exam item was underspecified. Distinguish the concepts: vestibular depth governs the SEAL and therefore RETENTION; palatal vault form governs resistance to lateral force and therefore STABILITY. A V-shaped vault, incidentally, is unfavourable in both respects.