Overview: Molecular Regulation of Mineralization and Its Failure: —From Disclosure of Mechanisms to Clinical Implications—

Bone is composed of a protein matrix containing embedded crystals of hydroxyapatite, a form of calcium phosphate. Mineralization, the incorporation of the mineral into the matrix, is an essential step for the bone to achieve the hardness and rigidity that enable the skeleton to resist gravitational and mechanical loading. Mineralization of vertebrates is generally classified into two types, physiological and pathological mineralization. Physiological mineralization is necessary for the formation of hard tissues and for their appropriate functions. In the human body, this type of mineralization occurs only in bone and teeth. On the other hand, pathological or ectopic mineralization of soft tissues is regarded as an important problem to be solved. Before presenting readers with the most recent biology of physiological and pathological mineralization, we will briefly review some basic knowledge on biomineralization from the historical aspect.