Lec 27 - Teeth

• The crown is the functional part of the tooth
• The root of the tooth is the portion that sits in the alveolar bony socket
• The mineralized components of teeth are

  • enamel
  • dentin
  • cementum
• The clinical crown is the portion of the tooth that sits above the gingiva
• The anatomical crown is the portion of the tooth encased by enamel
• Label the tooth

  A) enamel

  B) dentin

  C) gingiva

  D) odontoblasts

  E) gingival epithelium

  F) pulp chamber

  G) vessels and nerves

  H) periodontal ligament

  I) cementum

  J) root canal and apical foramen

  K) alveolar bone

  
• The periodontal ligament anchors the cementum to the alveolar bone
• Cementum covers the root of the tooth
• The first stage of tooth development is the bud stage. This is where neural crest cells will aggregate underneath oral epithelium. They will send signals for oral epithelium to invaginate into the underlying mesenchyme

  
• The second stage of tooth development is the cap stage. This is where the tooth bud indents to make a cap-like structure. Neural crest cells differentiate into dental papilla and mesenchymal cells differentiate into the dental sac. Eventually the papilla will become the pulp cavity

  
• The third phase of tooth development is called the late cap stage. This is when the epithelial tooth bud is lined by an outer and inner enamel epithelium. The inner enamel epithelium differentiates into a single layer of ameloblasts which will secrete enamel. Odontoblasts develop from the neural crest cells in the dental papilla and will secrete dentin
• The ameloblasts and odontoblasts have two different embryonic origins
• The dental sac gives rise to

  • cementoblasts that form cementum
  • cells that form the periodontal ligament
• In erupted teeth, the ameloblasts are gone and there is a loss of the mesenchyme that was supporting the ameloblasts. The ameloblasts will fluff off and there is nothing left to secrete enamel
• Dentin components

  • organic: 20% type I collagen (pre-dentin)
  • inorganic: 80% hydroxyapatite and fluorapatite
• Label the image of tooth

  A) pulp cavity

  B) odontoblasts

  C) apical side of odontoblasts secreting pre-dentin

  D) pre-dentin

  E) mineralized dentin

  F) enamel

  G) ameloblasts

  
• Dentin contains dental tubules which are spaces that extend from odontoblasts into the pre-dentin and dentin so that the processes of odontoblasts can reach the pre-dentin and dentin to maintain the tissue. Lines can be seen in the dentin which is a good histological indicator for dentin
• If you have sensitive teeth, your dentinal tubules are larger than normal, so signals from the external environment are more likely to reach the nerve. So toothpastes like sensodyne make the tubules smaller or plug them up
• These lines are an example of dentinal tubules

  
• Enamel components

  • organic matrix is made up of amelogenin and enamelin
  • inorganic: mineralized proteins (hydroxyapatite)
• Each ameloblast has processes that are going to make up the enamel rod. They have a secretory stage where the production of enamel matrix proteins occurs (amelogenin and enamelin to allow for mineralization) and maturation stage where the mineralization of enamel rods into the hardest material in the body
• Cementoblasts are in the periodontal ligament. They excrete cementum and get trapped in the matrix and become cementocytes inside of cellular cementum. Those cementocytes will eventually die and the cementum becomes acellular cementum
• Cementum is avascular so it gets its blood supply from the periodonal ligament
• The function of cementum is to anchor root to the periodontal ligament
• Cementum components

  • 50-55% inorganic (hydroxyapatite)
  • 45-50% organic (mainly type I collagen)
  • 12% water
• The periodontal ligament is made up of loose and dense connective tissue. Its function is tooth attachment and support. and It has high turnover rate.
• Label the following

  A) dentin

  B) acellular cementum

  C) cellular cementum

  D) cementum

  E) periodontal ligament

  F) alveolar bone

  
• Perforating fibers are thick bundles of type I collagen that anchors the periodontal ligament into the cementum and alveolar bone. This is the reason braces work
• Label the following

  A) enamel

  B) dentin

  C) gingiva

  D) pulp cavity

  E) cementum

  F) periodontal ligament

  G) alveolar bone

  H) apical foramen