B

Rapid healing of the extraction sockets during the first days–weeks after insertion causes marked soft-tissue contraction and early alveolar ridge resorption; this tissue change breaks the initial denture seal and makes the immediate denture feel loose, whereas the acrylic base itself does not appreciably shrink in that time frame [Feller 2013, PMID 24660412; Park 2010, PMID 20930364].