After extraction the maxillary residual ridge resorbs superiorly and inward (centripetal). The mandibular residual ridge characteristically resorbs:

The maxilla resorbs up and palatally (centripetal, arch gets smaller) while the mandible resorbs down and buccally/outward (centrifugal, arch gets relatively wider). This opposite pattern produces the long-term edentulous tendency toward a Class III ridge relationship.Other options: The mandible does not narrow inward, resorption is not limited to one surface, and ridges definitely resorb after extraction.Key exam takeaway: Maxilla resorbs up-and-in (smaller); mandible resorbs down-and-out (wider). Remember the divergent centripetal vs centrifugal pattern.