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Enamel & amelogenesis part 1

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Enamel is formed through the process of amelogenesis, which involves the life cycle of ameloblasts. Ameloblasts undergo morphological and physiological changes during the secretory, transitional, and maturative stages of amelogenesis. During the secretory stage, ameloblasts develop Tomes' processes which extend into the enamel matrix and help establish the rod and interrod structure of enamel. As enamel matures, ameloblasts transition to having microvilli and modulate between ruffled and smooth shapes to both remove organic material from the enamel and introduce inorganic minerals to fully mineralize the enamel.

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Enamel & Amelogenesis By Amira Mohsen Elsherbini
Enamel & amelogenesis part 1
Every one has a unique figure print¡­ ?Do you Know that you have a dental print that is as unique as your finger print?11 ?It is your ENAMEL
Whatdoyouthinktheproblem is?
Itmightbe ?Developmental ? (Amelogenesis and life cycle of ameloblast) ?External factor ? Properties (Chemical or Physical) ?Surface structure ? Structure of enamel , surface structure and hypocalcified structures.
So¡­.. By definition What is Enamel ??? ?The hardest calcified structure in the body ?Ectodermal in origin ?non-collagenous tissue ?covering the anatomical crown of teeth ? forming a protective converging against masticatory forces.
Enamel ? Acellular, ? inert, ?non vital and insensitive tissue, ?when destroyed by any means usually wear or caries it can not be replaced or regenerated.
PropertiesofEnamel Physical 1- COLOR 2-THICKNESS 3-HARDNESS 4- BRITTLENESS 5-solubility 6- PERMEABILITY chemical 1- Inorganic 2 - organic
Chemical composition Organic 4% ? 1-2% non-collagenous proteins ¡° Enamel proteins¡° ? 2-3% water. Amelogenin (90%) Non amelogenins (10%) Fine lacy network, forms an envelop surrounding each crystal. Non organic (mineral) 96% ? Calcium and phosphate in the form of hydroxyapatite crystals. Ca 10(PO4)6 (OH)2 ? Traces of strontium,magnesium, lead and fluoride
PhysicalProperties ? 1-COLOR YELLOWISH WHITE Translucent enamel GRAYISH WHITE Opaque enamel Depending on degree of translucency which depends on a. Degree of calcification. b. Homogenisity of enamel
PhysicalProperties ?2-Thickness ? Variable ? Maximum thickness (2.5 mm) at the cusp tip or incisal edge ? Thinnest at cervix where it ends at a feather edge. ? As a functional adaptation, thickness of enamel is more in lingual aspect of maxillary molars and buccal aspect of mandibular teeth, in relation to functional cusps.
PhysicalProperties ?3-Hardness ?Is the hardest calcified tissue in the body due to ? high mineral content & ? crystallite arrangement ?Enamel of the permanent teeth is harder than that of the deciduous one. ?Micro-hardness is grater at surface and cusp tip than ADJ and cervical line ?Hardness increase with flouride application.
PhysicalProperties ?4-Brittleness: ? Enamel is brittle (like glass) ? especially when it looses its foundation of elastic dentin ? Brittleness increase with ? age ? Undermining ? Non vital ?5-Solubility: ? Enamel is soluble in acids. ? Solubility depends on the presence of certain ions like fluoride. ? Surface enamel is less soluble.
PhysicalProperties ?5-Permeability ?It acts as a semi permeable membrane for some ions and dyestuffs of small molecular size through pores between the crystals. ?Permeability is mainly from saliva to the outer layer of enamel, but less from the pulp to the inner enamel layer across the dentin
Objectives ?Developmental ? (Amelogenesis and life cycle of ameloblast) ?External factor ? Properties (Chemical or Physical)? ?Surface structure ? Structure of enamel , surface structure and hypocalcified structures.
Enamel & amelogenesis part 1
Amelogenesis ?It can be divided into 3 main stages ? Presecretory stage. ?Secretory stage. ?Maturation stage.
Pre requesites of Amelogenesis
Story of Enamel formation Amelogenesis and life cycle of ameloblast) My old friend told me precious data
life cycle of ameloblast I. Morphogenic. II. Differentiation. III. Secretory. IV. Transitional. V. Maturative. VI. Protective. VII.Desmolytic
Enamel & amelogenesis part 1
Before we start ? What is Enamel? ? Every hard structure is formed by mineral deposition on collagen except Enamel ? At every stage ? stage of tooth dev ? Light microscope ? Electron microscope ? Nucleus ? Golgi and centriole ? Mitochondria ? attachment ? Basement membrane ? hard structure (if present) ? special ch.ch ? Nutrition
? The dentinal end of the ameloblast, at which enamel is formed, is called distal (former basal) ? The (apical) end facing the stratum intermedium is called basal or proximal.
? Ameloblasts during their life time undergo morphological and physiological changes that are directly related to their function. ? These changes can be described as life cycle of ameloblasts
Morphogenic stage stage of tooth dev ?
Morphogenic stage Electron microscope ? short columnar cells Nucleus ? oval and central & fills the cell body Golgi and centriole? proximal end Mitochondria ? dispersed Basement membrane ? separate the IEE from cell free zone and dp cell free zone ? acellular cell free zone ? Acellular It has argyrophil fibers and the cytoplasmic processes of the superficial cells of the
Morphogenic stage ? Electron microscope ? ? attachment ? proximal junctional complex ? hard structure (if present) ? --- ? special ch.ch ? IEE interact with the adjacent mesenchymal cells, determining the shape of D.E.J and the crown. ? Nutrition -? from dental papilla Cell free zone Cell rich zone
Differentiation (Organization / pre-secretory) stage
Differentiation ( Organization) stage ? stage of tooth dev ? early bell stage ? Light microscope ? Tall columnar cells (twice the size) ? Electron microscope ? ? Nucleus ? migrate to proximal end ? Golgi and centriole? distal end ? Mitochondria ? migrate proximally and Increase in no ? Attachment ? with migration of mitochondria ? Basement membrane ? separate the IEE from and dp ? Special ch.ch ? epithelial mesenchymal interaction
Induction and polarization Inner dental epithelium Proximal end Distal end Odontoblasts Cell free zone Cell rich zone CentrioleNucleus Golgi apparatus Mitochondria
Enamel & amelogenesis part 1
hard structure (if present) ? predentin formation. Nutrition ? from dental follicle.
secretory stage Two forms of Amelobalsts? With two different arrangements of Enamel flat basal region Tomes process
secretory stage The secretory ameloblasts are structurally suited for synthesis and secretion of enamel proteins. The cells have o many mitochondria, o Well developed golgi complex o and extensive cisterns of rough endoplasmic reticulum. Cytoplasm also shows many secretory granules, vacuoles, free ribosome, various types of Vesicles.
Messenger RNA carries the message from nucleus to cytoplasm (aminoacid sequence) ¡ý Ribosomes translate the message (enamel protein) ¡ý Protein is synthesized in rough endoplasmic reticulum (Amelogenin & Non-amelogenin) ¡ý Protein undergoes post translation modification in golgi complex ¡ý Packing of protein into secretory granules (stippled enamel) against first layer of dentin (nucleation site) Structure-less (rodless) enamel Ameloblasts synthesize enamel protein (1st form)
Reciprocal Induction Odontoblast Dentin matrix Ameloblast Enamel matrix (stippled?struc ture-less E) Dentin
? Starts at the cusp tip or the incisal edge and proceed cervically
Ameloblasts synthesize enamel protein (2nd form) : Tome¡¯s process ?As the first layer (little thickness) of enamel is deposited, the ameloblast migrate away from dentine surface, ameloblasts develop a conical process at the base, which is called Tomes¡¯ process. ? The distinction between process and cell body is clearly marked by distal junctional complex. ?This Tomes¡¯ process contains primarily secretory granules and small vesicles while cell body contains abundant synthetic organelles. ?Tome¡¯s process jut into newly formed E matrix giving it saw tooth appearance
Secretion of enamel is confined to two sites ? Adjacent to proximal part of the process close to junctional complex; resulting in formation of inter rod, this wall encloses a pit in which Tomes¡¯ process fits. ?one surface of Tomes¡¯ process (later on fill these pits with matrix). ? So, the crystal orientation and direction in the wall of pit differ from that in the pits giving the inter rod enamel and the filling area become the enamel rods. Inter rod is one step a head before the rod¡­. ?The Tomes' process that create the unique structure of enamel persist until final few increments in the surface are secreted (outer structureless enamel)
Enamel & amelogenesis part 1
Enamel & amelogenesis part 1
?The organic matrix of enamel consists of enamel protein, 90%of enamel protein is amelogenins and remaining of enamel protein 10% consist of enamelilin, tuftelin and amelin. ?The role of enamel protein is to provide an environment to accept mineral. ?Stratum intermedium with ameloblasts form a functional cellular unite responsible for E formation. ? SI plays a role in the formation of enamel itself; either through I. The control of fluid diffusion into and out of ameloblasts. II. The actual contribution of necessary formative elements or enzymes ¡°Alk. Phosphatase¡±.
Enamel & amelogenesis part 1
4-Transitional stage ? Withdrawal of Tomes¡¯ processes ?reduction in the height of the ameloblasts ?decrease in its volume and organelle content. ?During this period most probably the outer structureless or prismless enamel is formed. Outer structure less Inner structure less ADJ
Maturative stage ?Enamel maturation (full mineralization) occurs after most of the thickness of the enamel matrix has been formed in the occlusal or incisal area. ?In the cervical parts of the crown, enamel matrix formation is still progressing at this time.
Maturative stage In this stage ameloblasts have to introduce the inorganic material necessary for maturation and also reabsorb proteins and water to provide space for the minerals. ? In order to perform these dual functions -? Ameloblasts show Morphological alterations.
Changes in Ameloblasts ?Slight reduction in length. ?Cs are closely attached to enamel matrix. ?Cs contain cytoplasmic vacuoles containing material resembling enamel matrix. ?Display microvilli at their distal extremities forming a striated border ¡°increasing surface area¡± ? These structures indicate an absorptive function of these cells.
Cell modulation¡­ The cell alternate between ruffled and smooth ended shape (every 8 hr, ie 3 cycles/ day) expressed like a wave. ?Smooth ?Associated with removal of protein and water. ? Distal leaky junction and proximal tight junctions ?Ruffled ?Associated with introduction of inorganic materials. ?Distal tight and leaky proximal junctions.
Newly formed crystals Mature crystals The crystals thicken rapidly and the intervening protein is squeezed out.
Enamel & amelogenesis part 1
Protective stage
Protective ameloblast ? After complete enamel formation and full mineralization, ameloblast ? lose the ruffled border and become smooth. ? Secrete a protein between distal ends of cells and the enamel surface similar to basal lamina (hemidesmosomes)?which give firm attachment of ameloblast to the enamel. ?The columnar ameloblasts shorten to cuboidal ? and along with other collapsed layers of enamel organs (the stratum intermedium, stellate reticulum & outer enamel epithelium) form a 2¨C3 layered stratified epithelium which is termed as reduced enamel epithelium (REE).
Function of reduced enamel epithelium (REE). ? Protect the mature enamel by separating it from the C.T until the tooth erupt. ? Path way for eruption of the tooth by Contact with the oral epithelium. ? Form the primary epithelial attachment as an important role in establishing the dentogingival junction. ? enamel may be resorbed or cementum deposition may occur on enamel surface.
? enamel may be resorbed or cementum deposition may occur on enamel surface
Desmolytic Stage ?reduced enamel epithelium proliferates and seems to induce atrophy of the connective tissue separating it from the oral epithelium as pathway for tooth eruption. ?It is probable that the epithelial cells elaborate enzymes that are able to destroy connective tissue fibers by desmolysis. ? Premature degeneration of the reduced enamel epithelium may prevent the eruption of a tooth
Enamel dysplasia ? Interference with the secretion ? reduction in the amount &/or composition of the enamel matrix.
Defects of Amelogensis ? by febrile disease disturb the all teeth forming in this time characterized by distinctive bands of malformed surface enamel. On recovery, normal enamel resumed. ?by tetracycline induced disturbances in teeth, which incorporated in mineralizing tissues result in band of brown pigmentation or even total pigmentation. ?Fluoride ion chronic ingestion of F concentration in excess of 5 parts per million , result in mottled enamel as patches of hypomineralized and altered enamel.
Characteristic Features of Enamel are: 1. Ameloblasts, the enamel forming cells are ectodermal in origin 2. Enamel formation occurs only for a limited period of time till the desired thickness is formed 3. In an erupted tooth enamel is not lined by formative cells 4. Enamel does not have the capacity to repair or regenerate 5. Enamel is a nonliving tissue not containing cells or cellular components 6. Enamel is avascular and insensitive 7. Organic matrix of enamel is unique composed of enamel protein and is non-collagenous.

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Enamel & amelogenesis part 1

  • 1. Enamel & Amelogenesis By Amira Mohsen Elsherbini
  • 3. Every one has a unique figure print¡­ ?Do you Know that you have a dental print that is as unique as your finger print?11 ?It is your ENAMEL
  • 5. Itmightbe ?Developmental ? (Amelogenesis and life cycle of ameloblast) ?External factor ? Properties (Chemical or Physical) ?Surface structure ? Structure of enamel , surface structure and hypocalcified structures.
  • 6. So¡­.. By definition What is Enamel ??? ?The hardest calcified structure in the body ?Ectodermal in origin ?non-collagenous tissue ?covering the anatomical crown of teeth ? forming a protective converging against masticatory forces.
  • 7. Enamel ? Acellular, ? inert, ?non vital and insensitive tissue, ?when destroyed by any means usually wear or caries it can not be replaced or regenerated.
  • 9. Chemical composition Organic 4% ? 1-2% non-collagenous proteins ¡° Enamel proteins¡° ? 2-3% water. Amelogenin (90%) Non amelogenins (10%) Fine lacy network, forms an envelop surrounding each crystal. Non organic (mineral) 96% ? Calcium and phosphate in the form of hydroxyapatite crystals. Ca 10(PO4)6 (OH)2 ? Traces of strontium,magnesium, lead and fluoride
  • 10. PhysicalProperties ? 1-COLOR YELLOWISH WHITE Translucent enamel GRAYISH WHITE Opaque enamel Depending on degree of translucency which depends on a. Degree of calcification. b. Homogenisity of enamel
  • 11. PhysicalProperties ?2-Thickness ? Variable ? Maximum thickness (2.5 mm) at the cusp tip or incisal edge ? Thinnest at cervix where it ends at a feather edge. ? As a functional adaptation, thickness of enamel is more in lingual aspect of maxillary molars and buccal aspect of mandibular teeth, in relation to functional cusps.
  • 12. PhysicalProperties ?3-Hardness ?Is the hardest calcified tissue in the body due to ? high mineral content & ? crystallite arrangement ?Enamel of the permanent teeth is harder than that of the deciduous one. ?Micro-hardness is grater at surface and cusp tip than ADJ and cervical line ?Hardness increase with flouride application.
  • 13. PhysicalProperties ?4-Brittleness: ? Enamel is brittle (like glass) ? especially when it looses its foundation of elastic dentin ? Brittleness increase with ? age ? Undermining ? Non vital ?5-Solubility: ? Enamel is soluble in acids. ? Solubility depends on the presence of certain ions like fluoride. ? Surface enamel is less soluble.
  • 14. PhysicalProperties ?5-Permeability ?It acts as a semi permeable membrane for some ions and dyestuffs of small molecular size through pores between the crystals. ?Permeability is mainly from saliva to the outer layer of enamel, but less from the pulp to the inner enamel layer across the dentin
  • 15. Objectives ?Developmental ? (Amelogenesis and life cycle of ameloblast) ?External factor ? Properties (Chemical or Physical)? ?Surface structure ? Structure of enamel , surface structure and hypocalcified structures.
  • 17. Amelogenesis ?It can be divided into 3 main stages ? Presecretory stage. ?Secretory stage. ?Maturation stage.
  • 18. Pre requesites of Amelogenesis
  • 19. Story of Enamel formation Amelogenesis and life cycle of ameloblast) My old friend told me precious data
  • 20. life cycle of ameloblast I. Morphogenic. II. Differentiation. III. Secretory. IV. Transitional. V. Maturative. VI. Protective. VII.Desmolytic
  • 22. Before we start ? What is Enamel? ? Every hard structure is formed by mineral deposition on collagen except Enamel ? At every stage ? stage of tooth dev ? Light microscope ? Electron microscope ? Nucleus ? Golgi and centriole ? Mitochondria ? attachment ? Basement membrane ? hard structure (if present) ? special ch.ch ? Nutrition
  • 23. ? The dentinal end of the ameloblast, at which enamel is formed, is called distal (former basal) ? The (apical) end facing the stratum intermedium is called basal or proximal.
  • 24. ? Ameloblasts during their life time undergo morphological and physiological changes that are directly related to their function. ? These changes can be described as life cycle of ameloblasts
  • 26. Morphogenic stage Electron microscope ? short columnar cells Nucleus ? oval and central & fills the cell body Golgi and centriole? proximal end Mitochondria ? dispersed Basement membrane ? separate the IEE from cell free zone and dp cell free zone ? acellular cell free zone ? Acellular It has argyrophil fibers and the cytoplasmic processes of the superficial cells of the
  • 27. Morphogenic stage ? Electron microscope ? ? attachment ? proximal junctional complex ? hard structure (if present) ? --- ? special ch.ch ? IEE interact with the adjacent mesenchymal cells, determining the shape of D.E.J and the crown. ? Nutrition -? from dental papilla Cell free zone Cell rich zone
  • 28. Differentiation (Organization / pre-secretory) stage
  • 29. Differentiation ( Organization) stage ? stage of tooth dev ? early bell stage ? Light microscope ? Tall columnar cells (twice the size) ? Electron microscope ? ? Nucleus ? migrate to proximal end ? Golgi and centriole? distal end ? Mitochondria ? migrate proximally and Increase in no ? Attachment ? with migration of mitochondria ? Basement membrane ? separate the IEE from and dp ? Special ch.ch ? epithelial mesenchymal interaction
  • 30. Induction and polarization Inner dental epithelium Proximal end Distal end Odontoblasts Cell free zone Cell rich zone CentrioleNucleus Golgi apparatus Mitochondria
  • 32. hard structure (if present) ? predentin formation. Nutrition ? from dental follicle.
  • 33. secretory stage Two forms of Amelobalsts? With two different arrangements of Enamel flat basal region Tomes process
  • 34. secretory stage The secretory ameloblasts are structurally suited for synthesis and secretion of enamel proteins. The cells have o many mitochondria, o Well developed golgi complex o and extensive cisterns of rough endoplasmic reticulum. Cytoplasm also shows many secretory granules, vacuoles, free ribosome, various types of Vesicles.
  • 35. Messenger RNA carries the message from nucleus to cytoplasm (aminoacid sequence) ¡ý Ribosomes translate the message (enamel protein) ¡ý Protein is synthesized in rough endoplasmic reticulum (Amelogenin & Non-amelogenin) ¡ý Protein undergoes post translation modification in golgi complex ¡ý Packing of protein into secretory granules (stippled enamel) against first layer of dentin (nucleation site) Structure-less (rodless) enamel Ameloblasts synthesize enamel protein (1st form)
  • 36. Reciprocal Induction Odontoblast Dentin matrix Ameloblast Enamel matrix (stippled?struc ture-less E) Dentin
  • 37. ? Starts at the cusp tip or the incisal edge and proceed cervically
  • 38. Ameloblasts synthesize enamel protein (2nd form) : Tome¡¯s process ?As the first layer (little thickness) of enamel is deposited, the ameloblast migrate away from dentine surface, ameloblasts develop a conical process at the base, which is called Tomes¡¯ process. ? The distinction between process and cell body is clearly marked by distal junctional complex. ?This Tomes¡¯ process contains primarily secretory granules and small vesicles while cell body contains abundant synthetic organelles. ?Tome¡¯s process jut into newly formed E matrix giving it saw tooth appearance
  • 39. Secretion of enamel is confined to two sites ? Adjacent to proximal part of the process close to junctional complex; resulting in formation of inter rod, this wall encloses a pit in which Tomes¡¯ process fits. ?one surface of Tomes¡¯ process (later on fill these pits with matrix). ? So, the crystal orientation and direction in the wall of pit differ from that in the pits giving the inter rod enamel and the filling area become the enamel rods. Inter rod is one step a head before the rod¡­. ?The Tomes' process that create the unique structure of enamel persist until final few increments in the surface are secreted (outer structureless enamel)
  • 42. ?The organic matrix of enamel consists of enamel protein, 90%of enamel protein is amelogenins and remaining of enamel protein 10% consist of enamelilin, tuftelin and amelin. ?The role of enamel protein is to provide an environment to accept mineral. ?Stratum intermedium with ameloblasts form a functional cellular unite responsible for E formation. ? SI plays a role in the formation of enamel itself; either through I. The control of fluid diffusion into and out of ameloblasts. II. The actual contribution of necessary formative elements or enzymes ¡°Alk. Phosphatase¡±.
  • 44. 4-Transitional stage ? Withdrawal of Tomes¡¯ processes ?reduction in the height of the ameloblasts ?decrease in its volume and organelle content. ?During this period most probably the outer structureless or prismless enamel is formed. Outer structure less Inner structure less ADJ
  • 45. Maturative stage ?Enamel maturation (full mineralization) occurs after most of the thickness of the enamel matrix has been formed in the occlusal or incisal area. ?In the cervical parts of the crown, enamel matrix formation is still progressing at this time.
  • 46. Maturative stage In this stage ameloblasts have to introduce the inorganic material necessary for maturation and also reabsorb proteins and water to provide space for the minerals. ? In order to perform these dual functions -? Ameloblasts show Morphological alterations.
  • 47. Changes in Ameloblasts ?Slight reduction in length. ?Cs are closely attached to enamel matrix. ?Cs contain cytoplasmic vacuoles containing material resembling enamel matrix. ?Display microvilli at their distal extremities forming a striated border ¡°increasing surface area¡± ? These structures indicate an absorptive function of these cells.
  • 48. Cell modulation¡­ The cell alternate between ruffled and smooth ended shape (every 8 hr, ie 3 cycles/ day) expressed like a wave. ?Smooth ?Associated with removal of protein and water. ? Distal leaky junction and proximal tight junctions ?Ruffled ?Associated with introduction of inorganic materials. ?Distal tight and leaky proximal junctions.
  • 49. Newly formed crystals Mature crystals The crystals thicken rapidly and the intervening protein is squeezed out.
  • 52. Protective ameloblast ? After complete enamel formation and full mineralization, ameloblast ? lose the ruffled border and become smooth. ? Secrete a protein between distal ends of cells and the enamel surface similar to basal lamina (hemidesmosomes)?which give firm attachment of ameloblast to the enamel. ?The columnar ameloblasts shorten to cuboidal ? and along with other collapsed layers of enamel organs (the stratum intermedium, stellate reticulum & outer enamel epithelium) form a 2¨C3 layered stratified epithelium which is termed as reduced enamel epithelium (REE).
  • 53. Function of reduced enamel epithelium (REE). ? Protect the mature enamel by separating it from the C.T until the tooth erupt. ? Path way for eruption of the tooth by Contact with the oral epithelium. ? Form the primary epithelial attachment as an important role in establishing the dentogingival junction. ? enamel may be resorbed or cementum deposition may occur on enamel surface.
  • 54. ? enamel may be resorbed or cementum deposition may occur on enamel surface
  • 55. Desmolytic Stage ?reduced enamel epithelium proliferates and seems to induce atrophy of the connective tissue separating it from the oral epithelium as pathway for tooth eruption. ?It is probable that the epithelial cells elaborate enzymes that are able to destroy connective tissue fibers by desmolysis. ? Premature degeneration of the reduced enamel epithelium may prevent the eruption of a tooth
  • 56. Enamel dysplasia ? Interference with the secretion ? reduction in the amount &/or composition of the enamel matrix.
  • 57. Defects of Amelogensis ? by febrile disease disturb the all teeth forming in this time characterized by distinctive bands of malformed surface enamel. On recovery, normal enamel resumed. ?by tetracycline induced disturbances in teeth, which incorporated in mineralizing tissues result in band of brown pigmentation or even total pigmentation. ?Fluoride ion chronic ingestion of F concentration in excess of 5 parts per million , result in mottled enamel as patches of hypomineralized and altered enamel.
  • 58. Characteristic Features of Enamel are: 1. Ameloblasts, the enamel forming cells are ectodermal in origin 2. Enamel formation occurs only for a limited period of time till the desired thickness is formed 3. In an erupted tooth enamel is not lined by formative cells 4. Enamel does not have the capacity to repair or regenerate 5. Enamel is a nonliving tissue not containing cells or cellular components 6. Enamel is avascular and insensitive 7. Organic matrix of enamel is unique composed of enamel protein and is non-collagenous.