Calcium ions in amorphous calcium phosphate clusters (ACP)

Amorphous calcium phosphate (ACP) is a non-crystalline, metastable phase of calcium phosphate that serves as a vital intermediate in the formation of hydroxyapatite, the primary inorganic constituent of bone and teeth (Dey et al., 2010, Nature Materials). Within these amorphous clusters, often referred to as Posner's clusters (Ca9(PO4)6), calcium ions are held in a highly reactive and labile state, allowing for rapid release and transformation into crystalline mineral phases (Posner & Betts, 1975, Accounts of Chemical Research). Biologically, these clusters are essential for the controlled mineralization of the extracellular matrix, acting as a reservoir that prevents premature crystallization while ensuring a local supersaturation of ions (Habraken et al., 2013, Nature Communications). In therapeutic contexts, ACP is primarily utilized in dentistry, where it is often stabilized by casein phosphopeptides (CPP-ACP) to treat dental caries and white spot lesions by promoting enamel remineralization (Reynolds, 2008, Journal of Dental Research). The calcium ions released from these clusters interact with fluoride and phosphate to rebuild the mineral structure of the tooth, effectively reversing early-stage decay. Furthermore, ACP-based materials are employed in orthopedic applications as osteoconductive scaffolds that enhance bone regeneration and the integration of implants (Zhao et al., 2011, Biomaterials).

Other names

Amorphous calcium phosphatePosner's clustersNon-crystalline calcium phosphateACP clusters

Provides a labile source of calcium and phosphate ions to maintain mineral supersaturation and promote the formation of hydroxyapatite in hard tissues.