9 - Histogenesis of dentin - Dentinogenesis

Question 1

Dentin

Answer 1

• Formed in dental papilla by odontoblasts
• Odontoblasts differentiate from ectomesenchymal cells of dental papilla
• Reciprocal induction ⇢ when differentiated odontoblasts recieve signals to allow dentinogenesis to occur

Question 2

Stages of apposition

Answer 2

• Elongation of inner dental epithelium
• Differentiation of odontoblasts
• Formation of dentin + then enamel

Growth of tooth germ leads to:

• Bell stage
• histodifferentiation
• beginning of morphodifferentiation

Question 3

Dentinogenesis

Answer 3

Begins after final differentiation of odontoblasts

Odontoblasts formation is influenced by cells of inner dental epithelium

Membrane performativa:

• Basement membrane between enamel organ + dental papilla before dentin formation

Question 4

Odontoblasts

Answer 4

• Dentin-forming cells that differentiate from cells of dental papilla
• Ectomesenchymal cells enlarge + elongate ⇢ pre-odontoblasts
• Preodontoblasts cytoplasm ⇡ volume ⇢ to contain organelles for protein synthesis ⇢ odontoblast

Question 5

Stages of dentinogenesis

Answer 5

1. Formation of organic matrix

• Fibrogenesis
• Maturation of organic matrix

2.Mineralisation of organic matrix

• Globular calcification
• Linear calcification

Question 6

Formation of organic matrix - Fibrogenesis

Answer 6

Fibrogenesis

• Synthesis of type I collagen + its arrangement in fibrils
• Dentin formation begins w/appearance of collagen fibrils/Korff’s fibres + followed by type I collagen fibres
• Other components of matrix ⇢ non-collagenous proteins

1. Dentin phosphoprotein
2. Dentin sialoprotein

Question 7

Maturation of organic matrix

Answer 7

Organic matrix matures into:

• Pre-dentin ⇢ newly secreted unmineralised dentin consisting of ⇢ collagen, glycoproteins, proteoglycans ⇢ innermost region of dentin
• Mantle pre-dentin ⇢ odontoblasts ⇡ size + produce small vesicles w/collagen I fibrils (orient parallel to future DEJ)

Question 8

Mineralisation of organic matrix

Answer 8

• Single crystals appear within matrix vesicles
• Grow rapidly + vesicles rupture
• Clusters of crystallites (hydroxyapatites) ⇢ fuse w/adjacent clusters ⇢ forms continous layer of mineralised matrix

Question 9

Patterns of mineralisation

Answer 9

Globular calcification ⇢ fast rate of dentin formation

• Deposition of crystals in several discrete areas of matrix via heterogenous capture in collagen
• Crystals enlarge + can fuse to form a single calcified mass

Linear calcification ⇢ slow rate of dentin formation

Dentin formation allows 2 directions:

1. Spreads down from cusps - odontoblasts to enamel
2. Thickens - parallel to enamel layer