From Static Scaffolds to Dynamic Regeneration: A Narrative Review of Four-Dimensional Printing and Smart Scaffolds in Craniomaxillofacial Reconstruction.

BACKGROUND: Craniomaxillofacial bone defects are difficult to reconstruct because they combine irregular anatomy, functional loading, contamination risk, and high esthetic demands. Patient-specific 3D printing improves geometric reconstruction, but most conventional scaffolds remain static after implantation. Four-dimensional printing and stimuli-responsive smart scaffolds add a temporal dimension and may enable programmable shape change, controlled release, immunomodulation, antibacterial activity, vascular support, or electromechanical signaling. METHODS: A narrative review was conducted using PubMed, Web of Science, and Embase from database inception to May 25, 2026. Search terms combined 4D printing, 4D bioprinting, shape-memory polymers, stimuli-responsive hydrogels, smart scaffolds, craniofacial, maxillofacial, oral, dental, periodontal, bone regeneration, tissue engineering, vascularization, and angiogenesis. Eligible studies addressed 4D printing, 4D bioprinting, shape-memory scaffolds, stimuli-responsive hydrogels, or related smart biomaterials in craniomaxillofacial, oral, dental, periodontal, or bone-regeneration contexts. RESULTS: Four hundred nineteen records were identified. After duplicate removal and screening, 24 directly relevant articles were included for narrative synthesis. Current evidence centers on shape-memory polymers, stimuli-responsive hydrogels, magnetic-responsive composite scaffolds, near-infrared-responsive photothermal systems, antibacterial and immunomodulatory 4D scaffolds, and piezoelectric smart materials. Potential applications include curved calvarial defects, minimally invasive mandibular reconstruction, alveolar ridge augmentation, maxillary sinus floor elevation, infected bone defects, and oral bone regeneration. CONCLUSIONS: Four-dimensional printing and stimuli-responsive smart scaffolds suggest a transition from static replacement toward programmable, microenvironment-responsive regeneration. However, evidence remains predominantly preclinical. Future studies must define safe triggering conditions, in vivo shape-control accuracy, load-bearing reliability, degradation-regeneration synchrony, standardized manufacturing, and clinically meaningful endpoints before routine clinical use.