Tissue of the teeth Dr Jamal Naim PhD in Orthodontics Dentin

Compositions of dentin organic substance 30-25% from its weight About 90% collagen fibers About 10% ground substance inorganic substance 70-75% from its weight Hydroxyapatite crystallites

Properties of dentin Yellowish in color Elastic Less hard than enamel, but more than cementum Less radio-opaque than enamel, but more than cementum 3-10 mm thick

Life cycle of odontoblasts There are only 3 stages in the life cycle of odontoblasts: Differentiating stage Formation stage Quiescent stage

Cross section (A) Neural crest cells

Basement membrane ECTODERM MESODERM ectomesenchymal cells

Bud stage Future dental papilla

cap stage Future dental papilla

Life cycle of odontoblasts Differentiating stage: Before Differentiation the inner dental epithelium is separated from the dental papilla by the thin basement membrane. The undifferentiated peripheral cells are spindle and separated by great amount of ground substance In the early bell stage, under the inductive influence of the inner dental epithelium, the peripheral ectomesenchymal cells differentiate into preodontoblasts.

Life cycle of odontoblasts Differentiating stage Basement membrane preodontoblast Undifferentiated cell

Late Bell stage/differentiating stage for odontoblasts

Life cycle of odontoblasts They assume to a columnar shape and aligned as a single row along the basement membrane. Several projections arise from the upper part of the cells. The nuclei become basally oriented. The cells grow in length to become columnar (40u) Now the fully differentiated odontoblasts begin their work.

Life cycle of odontoblasts Formative stage: Concentration of the cell organelles, granular components and globular elements Production of the first amount of dentin (dentin matrix) The odontoblasts retreat from the basement membrane Leaving a single process which become enclosed in the dentinal tubule (tomes fiber). With successive deposition of dentin, tubule and process grow in length.

Life cycle of odontoblasts Differentiating stage/ Begin of formative stage predentin odontoblast Undifferentiated cell

Mitochondrion RER Formative stage Nucleus predentin Formative stage

Formative stage

Life cycle of odontoblasts Quiescent stage: Actively secreting odontoblasts decrease slightly in size. The odontoblastic process stop to elongate In this stage the odontoblasts produce only secondary dentin.

Life cycle of odontoblasts Quiescent stage: Odontoblasts decrease in size and function The dentin formation is reduced They produce now secondary and reparative dentin

Dentinogenesis Matrix Formation (forming predentin) Maturation Collagen fibers Ground substance Maturation (mineralization) Hydroxyapatite crystallites

Dentinogenesis Formation of predentin (dentin matrix): The first indication of forming predentin is the development of the KORFF FIBERS. They are bundles of fibrils among the odontoblasts They are perpendicular to the basement membrane and attached to it. This layer is main part of the MANTLE DENTIN

Basement membrane MANTLE DENTIN TOMES FIBER fibers are perpendicular to the basement membrane TOMES FIBER

Dentinogenesis The korffs fibers fade gradually and smaller fibrils form a network in the dentin subsequent to the mantle dentin, the CIRCUMPULPAL DENTIN. The odontoblasts form the main components of the dentin matrix, the collagen fibers and the mucopolysaccharides.

Basement membrane MANTLE DENTIN CIRCUMPULPAL DENTIN TOMES FIBER fibers are parallel to the DEJ TOMES FIBER

Dentinogenesis Maturation of predentin: It occurs parallel to matrix formation It begins at the tip of the crown It proceeds in a rhythmic pattern to gradually complete cervically. The first layer of predentin begins its maturation in a globular pattern (matrix vesicle), where small centers of calcification spread concentrically until they fuse together. If somewhere those globules do not fuse together, areas of uncalcified dentin are known as interglobular dentin.

Dentinogenesis The maturation goes then in linear or occasionally globular pattern. The mineralization begins by crystal deposition in form of fine plates of hydroxyapatite on the surface of the collagen fibrils. The long axes of the crystals are paralleling to the fibrils.

Maturation of dentin MANTLE DENTIN CIRCUMPULPAL DENTIN Mineralized MD Matrix vesicle Rupture of the MV and begin of mineralization Maturation of dentin

Maturation of dentin Matrix vesicle Begin of Crystallization Matrix vesicle Crystal lodgment Rupture of the MV and begin of mineralization Maturation of dentin