C

Distal-extension RPDs quickly lose their tissue support as the ridge settles during the first few weeks; once the thin cement/tissue-conditioning layer under the saddle has worn away, the base rocks and the mucosa is loaded, producing pain on chewing pressure. This early loss of basal adaptation is a well-recognized reason for post-insertion soreness and the need for an early re-line, whereas occlusal or clasp problems usually cause discomfort immediately after delivery, not weeks later [Hill & Rubel, 2011, PMID 21774874; Feit, 1999, PMID 10570592].