The Injectable Niche: 'Hydrogel-Based Stem Cell' Delivery for Alveolar and Craniofacial Bone Regeneration- A Narrative Review.

Background: Alveolar and craniofacial bone deficiency underlies treatment challenges in periodontics, implant dentistry, prosthodontics, oral surgery, cleft care, endodontics and orthodontics. Conventional grafting is limited by donor-site morbidity, finite volume and the absence of living cells in substitutes. Hydrogels, injectable water-swollen polymer networks that mimic extracellular matrix, combined with mesenchymal stem cells, particularly the readily accessible dental stem cells, represent a minimally invasive tissue-engineering alternative. Aim: To critically review the biological basis, material design and specialty-wise preclinical and clinical evidence for hydrogel–stem cell constructs in oral bone regeneration, and to identify barriers to translation. Methods: Narrative review of PubMed-indexed literature up to November 2026, prioritising systematic reviews, meta-analyses and controlled clinical trials, supplemented by key animal studies and foundational papers. Results: Hydrogel stiffness and stress relaxation regulate stem cell osteogenic commitment, and hydrogels improve cell retention, survival and growth-factor delivery. Dental pulp stem cells, stem cells from exfoliated deciduous teeth and periodontal ligament stem cells regenerate bone comparably to bone marrow stem cells in animal models. Clinically, cell-based constructs are consistently safe. Meta-analytic data show a modest advantage in new bone at six months in sinus augmentation and added attachment gain in intrabony defects, and a randomised cleft trial found tissue-engineered constructs comparable to iliac crest graft. Several randomised trials, however, found no significant benefit over conventional grafts, and the evidence is of low to moderate quality. Antibacterial, immunomodulatory, prevascularised, extracellular vesicle-loaded and 3D-bioprinted hydrogels are emerging. Conclusion: Hydrogel–stem cell constructs are biologically rational and safe, but not yet superior to established grafting. Mechanical reinforcement, vascularisation, infection control, cost-effective manufacturing and well-powered trials with functional prosthodontic endpoints are required before routine adoption.