Tooth Formation

Figure in class

Enamel

large dense hydroxyapatite crystals embedded in insoluble protein fiber network

• Very hard and resistant
• Small amount of mineral exchange with saliva
• Fluoride produces enamel 3X more resistant to caries in children
• Formed by special epithelial cells prior to tooth eruption

Dentin

hydroxyapatite crystals embedded in strong meshwork of collagen fibers

• Similar to bone but without cell, vessels and nerves
• Mineral deposition and resorption are about 1/3X of bone
• Deposited, nourished and maintained by odontoblasts lining pulp cavity wall

Cementum

almost identical to bone including cells

• Mineral exchange same as bone
• Collagen fibers extend from cementum into jaw bone to hold tooth in place
• Formed by cells of periodontal ligaments lining tooth socket

Pulp - connective tissue with nerve, vessels, lymphatics

20 deciduous teeth (erupt 6 mon-2 yrs), 28-32 permanent teeth

Fetal tooth formation process:

1. Epidermis of oral cavity grows into jaw mesenchyme and forms tooth bud (figure in class)
2. Outer layer of bud forms enamel
3. Inner layer of bud forms dentin
4. Crown is produced first, root next and cementum laid down
5. As teeth develop and jaw bone ossifies, teeth become surrounded by bony socket
6. As root elongates and bone ossifies, crown is pushed through the gum
7. Permanent teeth formed in same manner, stalk forms latera bud that lies lingual to deciduous teeth
8. As permanent teeth grow, deciduous roots are resorbed and only crown with upper root are shed
9. All molars are permanent teeth (1-3)
10. Rate of development and eruption increased by thyroid and growth hormones
11. Early salt deposition affected by availability of Ca and PO₄ and vitamin D, and rate of parathyroid secretion