Enameloid

Enameloid, also known as durodentine or vitrodentine, is an enamel-like tissue found in fish. It is the primary outer component of shark odontodes (teeth and dermal denticles),^[1][2][3] and modified forms of enameloid also occur in the teeth and scales of actinopterygian (ray finned) fishes and stem-group gnathostomes (jawed vertebrates).^[3] In extinct, armored jawless vertebrates such as heterostracans, enameloid forms the outer component of shell-like dermal armor.^[3][4] Although the origin of enameloid is debated, it is probably homologous to dentine rather than true enamel, despite its enamel-like strength and development. The term covers any hyper-mineralized tissue with an organic "scaffold" consisting of ectodermal and ectomesenchymal proteins.^[1][2][5]