A maxillary complete denture repeatedly loses its peripheral (border) seal and dislodges when the patient opens wide or moves the mandible. Which fault is MOST likely responsible?

Correct answer: C. An over-thick or over-extended distobuccal flange contacting the coronoid process

• A. An under-extended labial flange reduces retention passively and continuously; it does not produce the characteristic dislodgement tied to mandibular MOVEMENT.
• B. Relief over the incisive papilla prevents pressure on the nasopalatine neurovascular bundle. Excessive relief there might allow slight rocking but does not break the peripheral seal on opening.
• C. CORRECT. The distobuccal flange occupies the ZYGOMATIC-ALVEOLAR (coronoid) space. When the mandible opens or moves laterally, the CORONOID PROCESS of the mandible sweeps forward and medially into this region. A flange that is too thick or too long there is struck by the coronoid, which lifts the denture and breaks the border seal — the patient reports the upper denture dropping specifically on wide opening or chewing. The correction is to thin and reduce the distobuccal flange, not to add more material.
• D. A seal placed anterior to the vibrating line would be positioned on immovable tissue — an error, but one causing a persistent leak rather than movement-dependent dislodgement.

Note: Sort denture complaints by TIMING. Constant looseness = border extension or seal problems. Looseness only on FUNCTION = interference with a moving structure: coronoid at the distobuccal flange, buccal frenum, mylohyoid ridge or masseter groove in the lower denture.