Biomechanical advancements in hydroxyapatite, magnesium-substituted hydroxyapatite, and strontium-substituted hydroxyapatite in clinical and non-clinical studies for maxillofacial bone tissue engineering: A review

Hydroxyapatite (HA) is a bioceramic known for its bioactivity and osteoconductivity, which should make it an ideal candidate for maxillofacial bone regeneration. However, its brittleness limits its suitability for load-bearing applications. Over recent decades, substantial efforts have focused on enhancing its performance, particularly through ionic substitution, including magnesium-substituted HA (Mg-HA) and strontium-substituted HA (Sr-HA). This review summarises the available information on the structural, physical and mechanical properties of facial bones (maxilla, mandible, zygoma and frontal bone). The crystal structure, physical, and mechanical properties and in-vitro biological responses of dense and porous HA, Mg-HA and Sr-HA ceramics are described, with particular emphasis on synthesis routes and additive manufacturing technologies as well as their mechanical and in-vitro biological performance. Finally, clinical studies of HA-based scaffolds in human maxillofacial reconstruction alongside the use of Mg-HA and Sr-HA in clinical studies of small-animal cranial and periodontal models are highlighted.