Which of the following complications can occur due to an UNDER-EXTENDED denture flange?

An under-extended flange does not utilize all available denture-bearing area, resulting in: poor retention, poor stability, a sunken/collapsed facial profile (loss of lip support), and potential for air gap under the flange. The flange supports the facial musculature — insufficient extension fails to support the lips and cheeks, creating an aged, sunken appearance. An over-extended flange causes the denture to unseat during muscle movement (lip puckering).