Shape-Memory and 4D-Printed Polymers for Craniomaxillofacial Bone Reconstruction: From Self-Fitting Scaffolds to Clinical Translation

Reconstruction of craniomaxillofacial (CMF) bone defects remains demanding because the defects are irregular, three-dimensionally curved and functionally and aesthetically critical. Autologous bone carries donor-site morbidity, and most alloplastic and tissue-engineered alternatives are static, so gaps at the implant-bone interface frequently persist. Shape-memory polymers (SMPs) and four-dimensional (4D) printing introduce a different paradigm, in which a construct is programmed into a temporary shape and recovers a defect-conforming geometry in response to body temperature, near-infrared light, magnetic fields or water. Following the Scale for the Assessment of Narrative Review Articles (SANRA), PubMed/MEDLINE, Scopus and Web of Science were searched for literature published up to September 2026. This narrative review summarizes the clinical problem of CMF reconstruction, the molecular basis and programming of biomedical SMPs, the main polymer families, triggering strategies and fabrication routes. Preclinical evidence on self-fitting poly(epsilon-caprolactone) scaffolds, polylactide composites, photothermal and magnetic constructs, morphing membranes and alveolar socket fillers is critically discussed, together with degradation, osteoimmunomodulation, vascularization, sterilization, storage stability and regulation. Current evidence remains largely preclinical, limited to in vitro and small-animal studies. Finally, knowledge gaps and research priorities are outlined to guide the clinical translation of shape-memory and 4D-printed polymers in CMF surgery.