Origin and Evolution of Cementum as Tooth Attachment Complex

A general view of the origin and development of cementum is discussed. The evolutionary origin of the cementum is a lining bone tissue that ties the dermal bone to the dermal tooth in Ostradodermi (armored fish, Agnatha, cartilaginous vertebrate). The connective tissue around the dermal tooth forms it, and it is absorbed after connecting the tooth in tooth replacement. The odontoblast forming the dermal tooth loses its polarity, but the osteoblast which forms the lining bone remains multi polar. Connective tissue forming the dermal tooth has further developed to form the pedicle and fibrous tissue connecting the teeth and jaw bones in fish and amphibians. In reptiles, teeth unite to the jaws with the pedicle bone, which is formed from the periodontal connective tissue. The formation aspect of the pedicle on the jaws differs from the dentine surface of the tooth root, because the pedicle is deposited on the jaw after absorption, but is directly deposited on the dentine. Some parts of the pedicle show as Sharpey's fibers but others are similar to the hyaline cartilage structures. It has been shown that the formation mechanisms have two polarities, like the human periodontal membrane, between the jaws and tooth root. Cementum is deposited not only on the surface of the root but also on the tooth crown as coronal cementum in mammals. When the coronal cementum develops, the enamel surface is absorbed by dental follicle tissue in horses etc., the enamel development is partially inhibited and forms a rugged surface in elephants etc., and enamel reduction is seen in Berardius (tooth whale). The ivory (lateral incisor) of the elephant and the tusk of the walrus (Odobenus) are covered in thick cementum : this is a root cellular cementum with rhythmic incremental lines, because the top of it has thin enamel.