ODONTOBLAST

An odontoblast is a biological cell of neural crest origin whose main function is formation of dentin.
This slide gives a detailed explanation of the same.

1. ODONTOBLAST SHRAVYA.M

2. CONTENTS INTRODUCTION ORIGIN DEVELOPMENT LIFE CYCLE STRUCTURE OF ODONTOBLAST GENES ODONTOBLAST & DENTINOGENESIS ROOT DENTINE

3. BLOOD SUPPLY FATE OF ODONTOBLAST ULTRASTRUCTURE HISTOCHEMICAL STAINS IHC MARKERS CLINICAL CONSIDERATION REFERENCES

4. WHAT IS AN ODONTOBLAST?? An odontoblast is a biological cell of neural crest origin that is a part of the outer surface of the pulp and whose biological function is dentinogenesis,which is a creation of dentine. Dentine forming cells Ectomesenchymal origin

5. 2 nd most prominent cell in the pulp Large columnar cells Arranged in a palisading pattern at the pheriphery of the pulp Rich in ER, Golgi complex Unidirectional secretory pattern Interconnected by Macula adherens and gap junctions NOTE

6. No. of odontoblast = no.of dentinal tubules 59,000 -76,000/ sqmm Deposits 4µm of dentine everyday. Morphologic variations of odontoblasts : -Tall columnar cells in the crown of the tooth -Low columnar cells in the middle of the tooth -Flattened cells at the apex NOTE

7. STAGES OF TOOTH DEVELOPMENT BUD STAGE

8. CAP STAGE

9. EARLY BELL NOTE: Pre Ameloblasts Are First Formed Which Then Influences The Formation Of Pre Odontoblasts

10. ADVANCED BELL STAGE

11. LIFE CYCLE PRE-ODONTOBLAST STAGE SYNTHETIC ODONTOBLAST STAGE TRANSITIONAL ODONTOBLAST STAGE RESTING STAGE ODONTOCYTES

12. Life cycle of odontoblast PRE-ODONTOBLAST STAGE : - Preodontoblasts have a small ovoid cells with small nucleus - few strands of dense fibrillar material radiating from the fibrillar center . -↑nuclear- cytoplasmic ratio - few orgenells -T he cells are located around the growing tip of the root -BMP ,GDf11 , BSP genes

13. `

14. SYNTHETIC / ACTIVE STAGE : -Tall columnar cells -Large basal nucleus with a basophilic cytoplasm -Numerous endoplasmic reticulum, mitochondria -Well developed golgi complex - Abundant synthetic orgenelles -Numerous secretory granules. TRANSITIONAL / INTERMEDIATE STAGE: -Shows features of synthetic cells but orgenells are less in number and less prominent. -Nucleus shows condensation of chromatin with orgenells distributed around the nucleus. -↓ secretory granules - Autophagic vacuoles

15. RESTING / AGED ODONTOBLAST STAGE : -Stubby cells -Scanty cytoplasm -Dark close faced nucleus -↓ Orgenelles - Secretory granules are absent

16. STRUCTURal DEVELOPMENT OF ODONTOBLASTS PREODONTOBLASTS - ↑NUCLEUS-CYTOPLASMIC RATIO & few cisterns of rough endoplasmic reticulum , small golgi apparatus and few mitochondria. 1 ST SIGN OF ODONTOBLAST DIFFERENTIATION- apical point of dental papilla during early bell stage. ↑ Aperiodic fibrils ̃15-20nm in diameter and 0.5-1µm long are perpendicular to basal lamina.

17. PREODONTOBLASTS

18. Cytoplasmic Processes Of The Adjascent Preodontoblasts Become Closely Associated With The Aperiodic Fibrils And Contact The Basal Lamina. Simultaneously polarisation of preodontoblasts begin. NOTE

19. It has been suggested that receptor- ligand interactions involving substrate adhesion molecules among the aperiodic fibrils serve to orient and immobilize the preodontoblasts , inducing them to begin differentiation . AND ODONTOBLASTS ARE THUS FORMED. NOTE

20. GENES REGULATING THE ODONTOBLAST DIFFERENTIATION BMP (BONE MORPHOGENETIC PROTEINS) ACTIVIN FGF(FIBROBLAST GROWTH FACTOR) WNT (Wingless homologue in vertebrates) Lhx6 ,Lhx7 (Lim- homeobox domain gene) Barx1 ( BarH like homologue in vertebrates) Msx , Msx2 ( Msh -like genes in vertebrates) Dix1, Dix2 ( Distaless homologue in vertebrates) Pax9 (Paired box homeotic genes) Gli1 ,Gli2 , Gli3 ( Glioma associated oncogene homologe ) Lef1 (Lymphoid enchancer – binding factor) GENES REGULATING ODONTOBLAST DIFFERENTIATION

21. ODONTOBLAST DIFFERENTIATION

22. ODONTOBLAST DIFFERENTIATION

23. Migration Golgi apparatus,RER basement membrane Nucleus proximal end ↑number of RER ↑size of Golgi complex ↑number of mitochondria Numerous matrix vesicles Thus Odontoblasts exhibit cylindrical shape. CELLULAR CHANGES

24. STRUCTURE OF An ODONTOBLAST Approx 5-7µm in diameter 25-40µm in length Adjacent cells are connected by junctional complexes Shape of odontoblast ἀ Degree of Activity Cytoplasmic extensions at the apical end continue as Odontoblastic processes .

25. NUCLEUS SECRETORY VESICLES STRUCTURAL POLARITY MITOCHONDRIA GOLGI COMPLEX RER

26. ENDOPLASMIC RETICULUM The endoplasmic reticulum is a membrane-bound structure that is a part of every eukaryotic cell. FUNCTIONS: -Synthesis of various proteins and carbohydrates -Transports the vesicles to the golgi complex

27. As the proteins travel through the organelle, they create small pockets. -These pockets pinch off from the organelle and form vesicles . -The vesicles transport the proteins to the Golgi complex, where they are processed and distributed to different cells. Their number increases from from pre- odontoblast stage to active stage and further reduces as the cells reach quinesence .

28. GOLGI COMPLEX The golgi complex appears as an aggregation of smooth walled vesicles and cisternal profiles organised into distinct and separate groups Functions: *Synthesis of complex carbohydrates * Sulfation of proteins.

29. Matrix vesicles Site of initial mineralization. They are small membrane bound structure that buds off from the cell to form an independent unit. * They contain alkaline phosphatase , calcium adenosinetriphosphatase , metalloproteinases , proteoglycans , sulfur and calcium. .

30. *Microanalysis of Matrix vesicles indicates CALCIUM and SULFUR PEAK of matrix vesicles are higher than the odontoblast cytoplasm

31. ODONTOBLAST PROCESSES Tomes fibres Is the secretory pole of odontoblast Form the major content of dentinal tubules 3-4 microns in diameter at pulpal end and taper to 1 micron near the periphery. Cytoplasmic orgenells are also present close to the cell body. Their extension into the dentinal tubules varies Enamel spindles

32. They play a major role in predentine deposition Also the secretory granules on these processes are the precursors for peri -tubular dentine.

33. Coated vesicles and Coated pits reflect pinocytotic activity along the odontoblastic process at the level of predentine close to cell body .

34. Cytoskeleton A well-developed system of microtubules is present both within the cell body and the odontoblast process. Each microtubule is about 25 nm wide with a wall approximately 7-8 nm thick Functions of microtubules - transportation of intracellular substances stabilises cellular shape These cytoplasmic filaments are usually more highly concentrated at the cell periphery, forming distinct bands just beneath the cell membrane.

35. Nucleus Nuclear changes in various stages of odontoblast differentiation: a) Pre- odontoblast stage : *These cells present moderately reticulated nucleoli that tend to be circular in shape. *The nucleolar area is 0.55µm * Few strands of dense fibrillar material radiating from the fibrillar center *Located at the growing tips

36. FC Fg d NUCLEAR BODY I

37. b) Secretory Stage : * characterized by a large, irregular, and reticulated nucleolus. * Size 1.24µm *71% is occupied by dense fibrillar component. *2 fibrillar centres . *Prominent interstitial space *Chromatin clumps *Located at the apical region

38. c) Transitional stage : *Seen only under electron microscope *Nucleus is displaced from the basal extremity *Nucleolus is reduced in size *Size- 0.54µm *Granular layer is clearly seggregated *Highly condensed chromatin *Located at the middle region

39. d) Aged Odontoblast stage Small, compact haematoxyphilic nucleolus 0.39µm Segregated components Large lipid filled vacuoles in the cytoplasm Located at the coronal region. The fibrillar center remains connected on one side to the dense chromatin that encloses the nucleolus.

40. AGED ODONTOBLAST TRANSITIONAL ODONTOBLAST SECRETORY ODONTOBLAST PREODONTOBLAST

41. They possess junctional structures constituted by – Gap - Tight junctions - Desmosomes . Gap junctions and Tight junctions of focal or macular type appear on early odontoblasts during differentiation. JUNCTIONS

42. GJ GAP JUNCTIONS - Occur on the lateral surface of the cells at the Base. -They can form,dissolve & reform as the function dictates.

43. TIGHT JUNCTIONS: *Freeze fracture image of a tight junction *Extensive and branched rows of zipperlike particles.

44. ODONTOBLAST & DENTINOGENESIS After the differentiation of odontoblasts , the odontoblast starts functiong by depositing Von Korffs fibres (Type III collagen) They extend towards the IEE and fan out on the ground substance. As the odontoblasts increase in size they deposit Type I collagen that orient parallel to the future DEJ. Thus a layer of mantle dentine (15-20mm thick) is formed by odontoblasts .

45. Odontoblast depositing coronal mantle predentine

46. MATRIX VESICLES contain Alkaline Phosphatase -↑ concentration of phosphates + Calcium → Hydroxyapatite Crystals . Crystals- grow rapidly, rupture the matrix vesicles The process continues … Spread -clusters of crystallites → fuse with adjacent clusters to form a continuous layer of mineralized matrix Initially- on the surface of the collagen fibrils and ground substance, later within the fibrils- aligned with collagen.

47. Various Matrix Proteins Influence Mineralization: DPP - Binds to Ca, Controls Growth of H.A Crystals Osteonectin - Inhibits growth of H.A crystals, promotes their Binding to Collagen Gla -proteins, Phospholipids- Act as nucleators to concentrate calcium. Proteoglycans - inhibit premature mineralization seen in predentin .

48. COLLAGEN SYNTHESIS BY ODONTOBLASTS Hydroxylation of procollagen with N- and C- terminal extensions. Prolylhydroxylase Lysylhydroxylase . Triple helix assembly Triple helix formation Golgi complex Glycosylation Transported Procollagen COLLAGEN +n of O-linked galactose residues Trans- face

49. Pathway of Collagen synthesis in odontoblast

50. SECONDARY AND TERTIARY DENTIN Secondary dentin is deposited after root formation is completed and is formed by the same odontoblasts that formed primary dentin. Tertiary dentin is deposited at specific site in response to injury by damaged odontoblasts /replacement cells from pulp.

51. Root dentine formation Begins once Enamel & Dentin formation reaches the future CEJ. Initiated by Cells of HERS- which induce odontoblast differentiation. Collagen fibres - parallel to CDJ. Less mineralized, less number of Tubules. Complete- 18mths after eruption-Primary 2-3 yrs - Permanent Teeth

52. BLOOD SUPPLY Capillary supply in the subodontoblastic layer They migrate between the odontoblasts and regress.

53. FATE OF ODONTOBLASTS Life span of odontoblasts is equal to that of a viable tooth because once differentiated they cannot undergo further cell division. Resting Odontoblasts involved in secondary dentinogenesis is renamed as “ ODONTOCYTES ” because their function and properties are similar to osteocytes . These odontocytes may participate during reactionary dentinogenesis Gene DMP1 is involved in the differention of secretory odontoblasts into odontocytes

54. Ultrastructure

55. Histochemical Stains  The Phosphophoryn content of the odontoblast are retained in the sections during the specimen preparation and stained selectively in situ. Various stains for dentine are:  Haematoxylin & Eosin Methylene blue Alcian blue PAS Modified Gallego stain Ruthenium red

56. IHC MARKERS Murine Dentin Matrix Protein 1 (Dmp1) Dentin Sialophosphoprotein (DSPP) S 35 P 33 3 H -Serine 3 H - Proline Actin Tubulin Vimentin

57. Clinical significance 1)Pathological differences in the functional life cyle of odontoblasts – DENTINOGENESIS IMPERFECTA

58. 2)Pre- odontoblasts do not differentiate into odontoblasts – Shell/ Thistle-tube teeth 3) Odontoblasts do not differentiate into Osteocytes – Pulpal obliteration 4) Outward resorption of dentinal tubules by odontoclasts results in pulpal tissue appearing pink through the thin enamel – Pink Tooth

59. TO SUMMARIZE:

60. REFERENCES Nanci . A: Ten cates oral histology, 8 th ed , Elsevier Kumar. G S : Orban’s Oral histology & embryology, 13 th ed , Elsevier Berkovitz . B K B: Oral anatomy , Histology and Embryology,3 rd ed , Mosby Jose.M : Essentials of Oral Biology, CBS

61. Sasaki T, Garant P “Structure An Organization Of Odontoblasts ” , The Anatomical Record245:235-249(1996) Couve E “ Morphometric Analysis Of The Nucleolus During The Life Cycle Of Human Odontoblasts ”, The Anatomical Record 213:215-224(1985) A. Nanci , M. Fortin, And L. GHITESCU “ Endocytotic Functions Of Ameloblasts And Odontoblasts:lmmunocytochemical And Tracer Studies On The Uptake Of Plasma Proteins” , THE ANATOMICAL RECORD 245219-234 (1996) Ushiyama J, “Gap Junctions Between Odontoblasts Revealed By Transjunctional Flux Of Fluroscent Tracers”, Cell Tissues Res 258-611-616(1989)

62. Arana VE , Katchburian E, “Development Of Tight Junctions Between Odontoblasts Innearly Dentinogenesis As Revealed By Freeze-fracture” . The Anatomical Record 248:332-338(1997) Sigal M J , Pitaru S, Aubin JE,Cate T, “A Combined Scanning Electron Microscopy And Immunofluorescence Study Demonstrating That The Odontoblast Process Extends To Dentinoenamel Junction In Human Teeth.” The Anatomical Record 210:453-462(1984)

63. Corrections Add Odontoblast sensitivity –fluid dynamic theory Difference between tomes granular layer & granular process