Enamel 1

Question 1

What are the properties of Enamel?

Answer 1

• acellular, non-vital, non-vascular
• Ectoderm origin –> product of enamel organ
• most mineralized tissue in the body
• Brittle
• Thicker at crown ~ 2.5mm
  
  • 96% inorganic, 3% water by weight

Question 2

What are the major enamel proteins?

Answer 2

• amelogenins, ameloblastins, enameling, tuftelin

- NO COLLAGEN

Question 3

What are the enamel crystals?

Answer 3

• Mineral component of enamel
• carbonate can substitute for the phosphate
• HA will also incorporate Mg and F
  
  • carbonate and Mg will incorporate at inner enamel while F will do outside
• Hexagonal in shape, when fully mature it loses its shape
  
  • 60-70nm wide
  • 25-30nm thick
• may run entire length of the enamel layer

Question 4

How are the enamel rods composed?

Answer 4

• Generally run perp. to the DEJ
• no competely straight, curve as they move towards the surface
• organized into rows, which run in alternating directions
  
  • 1 ameloblast per rod
  • forms meshwork of cylinders

Question 5

What is the rod sheath?

Answer 5

• protein rich area that surround the rods
  
  • runs about 3/4 around a rod, separating it form interred enamel
  • the gaps is when rod and interred are continuous
• Rod sheath proteins
  
  • Ameloblastins and amelogenins

Question 6

What is interrod enamel?

Answer 6

• Different crystal orientation
• fills the gaps between rods
• caries penetrate through the higher protein rod sheath

Question 7

How does the formation of enamel occur?

Answer 7

• Starts at the inner enamel epithelium
• formation of first pre-dentin by odontoblasts
• ameloblast activation and deposition of enamel
  
  • initial deposition only around 30% mineralized

Question 8

What are the phases of Ameloblast maturation?

Answer 8

1) Pre-secretory: mature from pre-ameloblasts to ameloblasts
2) Secretory: deposition of enamel
3) Maturation: reduction of organic matrix, increase mineralization via ion transport

Question 9

How is enamel deposited forming the tooth?

Answer 9

• Cells deposit matrix apically via vesicles
• Basal lamina separating pre-dentin and ameloblasts is penetrated by cell projections and broken down
• Enamel is laid down directly in apportion to pre-dentin/mantle dentin
• TOMES PROCESS: projections into the developing enamel and is the site of much secretory activity
  
  • Effectively form the enamel rod structure
  • Distal: towards the forming enamel
  • Proximal: towards the stratum intermedia
  • Interrod first, then forms a groove into which rods are formed
  • Tomes Process = Rods

Question 10

How does enamel mature?

Answer 10

• Loss of stellate reticulum and fusion of the OEE and IEE result in a single layer of reduced enamel epithelium
• Prior to eruption, enamel hardens
  
  • quite slow, up to 5 years for perm. teeth
• Production of unique basal lamina and external enamel surface
  
  • disruptions of proteins inflaming can lead to enamel hypoplasia
• Modulation: process by with water and proteins are removed
  
  • Ruffled Cells: infiltration and incorporation of calcium ions into crystals occurs during this stage, low pH facilitates maturation
  • Smooth cells: allow diffusion out of protein fragments out of enamel, which leak in between cells and laterally defuse through cell layer

Question 11

What is the fate of the enamel organ?

Answer 11

• Fusion to form reduced enamel epithelium
• Remains of the organ attack to the tooth until eruption
  
  • remenats fuse with the oral epithelium, forming a cover
• After eruption anything left over (cells/basal lamina/etc.) form a membrane –> Nasmyth’s membrane
• The Primary enamel cuticle: mineralized coating, the last secretory product form the ameloblasts
• The secondary enamel cuticle: formed from remains of the reduced enamel epithelium merged with the oral epithelium