Dentin by PGT student of MDS pedo depart

dentin as a whole decribed briefly

1. Dentin Guided by- dr.barun dasgupta Dr. swati singh Dr. seema qamar Dr.Arnab mondal Presented by – Dr. Manshi Maharaj( PG 1 st year) dentin

2. contents Introduction Development of dentin ( Dentinogenesis ) Physical & chemical properties of dentin Structure Types of Dentin Age and functional changes in dentin. Innervation in dentin Developmental disturbances Clinical significance of dentin Conclusion References

3. INTRODUCTION dentin is a hard tissue of the tooth that surrounds the pulp & makes up the bulk & general form of tooth . it determines the crown shape & cusp & ridges & the no. & sizes of the roots. characterised by presence of tubules throughout its thickness. dentin is a living or vital tissue as it contains within the process of the specialized cells , the odontoblast.

4. Dentinogenesis Dentin formation - begins in late- bell stage Dentin formed by odontoblast cells – differentiate from Ecto - mesenchymal cells of dental papilla The dental pulp also develops from dental papilla which is mesodermal in origin. Hence called Dentin – Pulp complex (D- P organ)

5. Dentinogenesis consists of 3 stages: Cyto- differentiation. Matrix formation. Mineralization.

6. Cyto- differentiation Describes how odontoblasts differentiate from Undifferentiated mesenchymal cells Cells of dental papilla resembles the typical undifferentiated cells At the bell stage  differentiation of odontoblasts takes place, Starting at cuspal or incisal region Which involves - various growth factors The cells become cylindrical  referred as Pre-odontoblast Cells change their shape ,short cuboidal to columnar

7. Cell organelles markedly increase. Nucleus moves away from basement membrane – reversal of polarity Cells - called odontoblasts  secrete pre-dentin. Once the formation of pre-dentin at cuspal / incisal region begins the differentiation of new odontoblasts takes place further apically in dental papilla.

8. Initially daily increments – approximately 4 µm/day formed Once crown formation completes – dentin formation slows down to 1µm / day The root dentine formation – requires proliferation of epithelial sheath[ hertwig’s epithelial root sheath]

9. Matrix formation Differentiated odontoblast will have all features of the secretory cell abundance of rough endo- plasmic reticulum, a well developed golgi apparatus, mitochondria and secretory granules. pro- collagen synthesized in the rough endoplasmic reticulum transferred to golgi - apparatus, -- finally appear in secretory granules

10. VonKorff’s fiber . Argyrophilic fiber Believed to be - - bundles of collagen formed by odontoblast But recent ultra- structural studies reveal – these are due to staining of ground substance in cells & not collagen As the matrix formation continues – odontoblast leaves extension  odontoblastic process

11. Mineralization Occurs in globular pattern. Earliest crystal deposition – is in the form of very fine plates of hydroxyl- apatite on the surface of collagen fibrils and in the ground substances. Subsequently, these crystals are laid down within the collagen fibrils. arranged with their long axis parallel to the fibril axis, and in rows confirming 64nm striated pattern.

12. This crystal deposition appears to takes place from a common center called  spherilulite form  300 times smaller than enamel crystals.

13. Physical Properties color young age – light yellow with advancing age - becomes darker consistency Viscoelastic ( 8 6 GP a ) a nd s u b j ec t to s l i g h t de f o r m a t i o n unlike enamel (11-20GPa) which is hard and brittle. Harder ( 6 8 k g / mm 2 ) t han b o ne but c o nsi de r abl y s o f t er than enamel(343kg/mm 2 ) hardness of dentin slightly varies between tooth type & between crown & root dentin. hardness – 80 khn other properties proportional limit – 148 mpa compressive strength – 305 mpa Tensile strength - 51.5 mpa

14. Chemical properties Composition Organic matter – 35% Inorganic matter – 65% Ref - The role of dentin ECM in dentin formation and mineralization Michel Goldberg ,  Askok B Kulkarni ,  Marian Young ,  Adele Boske Type I collagenous fibrils Type V collagenous fibrils (minor) Non collagenous proteins: Dentin phosphoprotien (DPP) Dentin matrix protein 1 (DMP1) Dentin sialoprotein (DSP) Bone sialoprotein (BSP) Osteopontin , Osteocalcin Proteoglycans Phospholipids Growth factors: Bone morphogenetic proteins (BMP) Insulin like growth factors (IGFs) Transformin g growt h factor s β ( T G F - β ) Organic matrix

15. Hydroxyapatite crystals – several thousands unit cells Each crystal has a basic chemical formula 3Ca 3 (PO 4 ) 2 . Ca(OH) 2 Plate shaped Also contains traces of phosphates and sulphates Smaller than the hydroxyapatite crystals of enamel Inorganic matrix

16. structure Odontoblasts are present in the pulp & are arranged in a layer lining the pulpal surface of dentin Each cell gives out a long thin process which enters a hollow tube like structure within the dentin called as dentinal tubules Dentin is made up of numerous dentinal tubules Dentin forming cell is called as odontoblast

17. Odontoblast Terminally differentiated cells Aligned along Pulp periphery Pseudo stratified  crown Single layer  Root 25- 60  m in length & 4- 7  m diameter Oval nuclei & eccentric towards pulp Cell organelles present

18. Odontoblastic process Arise at predentin border Enter the dentinal tubules within in the tubule it runs in mineralized matrix Which contains some mitochondria Larger in diameter (3- 4µm) near the pulp and taper to 1µm approximately further into the dentin. Give lateral branches divide near the DEJ and may extend into enamel- - enamel spindles. Has microtubules, vesicles, mitochondria

19. Dentinal Tubules The course of the dentinal tubules follows a gentle curvature in the crown which resembles “S- shape ( sigmoid course ). These curvature are called as primary curvature Ends perpendicular to DEJ & DCJ Branches of the tubules near terminal are refer as terminal branch

20. Primary curvatures In root dentin & cuspal - incisal edges  tubules straight Placed a part in the periphery and closely packed near the pulp Secondary curvatures During the deposition of dentin, the odontoblast makes slight undulations that creates wavy dentinal tubules  This waviness of the dentinal tubules is called secondary curves Sinusoidal in shape

21. Thickness of dentin – 3-10 mm Thicker in male > then female Buccal surface > lingual surface Mesial = distal The diameter is more at pulpal end (3- 4µm) and smaller at their outer end (1µm) The ratio beween outer & inner surface of dentin is approx. 5 : 1 The ratio between the no. of tubules per unit area on the pulpal end and outer surface of the dentin is about 4:1 No. of tubules per square millimeter varies from 15000 at the DEJ to 65000 at the pulp – density and diameter increases with depth

22. Tubules have lateral branches throughout dentin  Canaliculi or microtubules - - at right angle to main tubule ; 1µm in diameter and 2µm in length Dentinal tubules have complex branching system Major: terminal branches ‘Y’ shaped Minor: 45° to main tubules A few odontoblastic processes extend through the DEJ into the enamel several millimetres . These are called – enamel spindles

23. Dentinal fluid The dentinal fluid – occupy space between the dentinal tubule and odontoblastic process Contains plasma proteins, and fibrinogen. equivalent to tissue fluid, proteoglycans, glycoproteins.

24. Peritubular / Intratubular dentin surrounds the dentinal tubules highly mineralized (approx.9%) than inter tubular dentin. forms collar around the dentinal tubule twice as thicker in outer dentin ( 0.7 µm ) than in inner dentin ( 0.4 µm) constricts the tubules to 1 µm at DEJ. Because of its high mineral content, it is lost in decalcified sections Calcifie d tubu l e w a l l ha s a n i nn e r or g a n ic l i n i ng t e rme d t h e L a mi n a Limi t a n s w h i c h i s h i g h in glucosaminoglycans (GAG)

25. Intertubular dentin Present between zones of tubular dentin. Forms main body of dentin and highly mineralized. Matrix consists – randomly arranged collagen fibers around the dentinal tubules Fibers are 0.2 µm – 0.5 µm in diameter & have striation at 64µm intervals. This dentin retains after decalcification. The hydroxy apatite crystals ( 0.1 µm in length ) – formed along the fibers with their long axis parallel to collagen fibers. Provide tensile strength to dentin

26. Pre dentin First formed dentin not mineralized located adjacent to odontoblasts It is around 2- 6µm wide The pre dentin appear to be pale staining than the mineralized dentin. As this matrix mineralized – becomes dentin and new layer of predentin is formed circumpulpally

27. TYPES OF DENTIN orban’s , oral histology , embryology and physiology ( 16 th edition )

28. PRIMARY DENTIN Dentin that is formed prior to eruption of a tooth. Classified as Orthodentin , the tubular form of dentin lacking of cells found in teeth of all dentate mammals Secreted at a relatively higher rate Constitutes m ajo r pa r t of t h e dentin in the tooth

29. first formed dentin present below the DEJ. most peripheral portion of primary dentin – 20µm thick organic matrix consists of collagen fibers which are perpendicular to DEJ These fibrils are larger than circumpulpal dentin slightly less mineralized than the circumpulpal dentin. The larger diameter collagen fibers ( 0.1 – 0.2 µm in diameter as von Korff”s fibers . MANTLE DENTIN

30. When viewed under polarised light, the mantle dentin (RED Band) can be differentiated from the Circumpulpal dentin (Purple with black dentinal tubules) This is due to difference in collagen fibres in mantle dentin

31. Circumpulpal dentin Forms remaining bulk of tooth represents the dentin - - formed prior to root completion Collagen fibrils are smaller & is more mineralized compared to mantle dentin collagen fibrils are closely packed each other

32. Hydroxy appatite crystals are deposited on the surface and within the fibrils and continue to grow as mineralization proceeds, resulting in an increased mineral content of dentin Circumpulpal dentin is mineralised through calcospherites in the mineralisation front between predentin and mineralizing dentin As the calcospherites enlarge, they fuse with the adjacent calcospherites until the dentin matrix is completely mineralised

33. Develops after root completion Narrow band of dentin surrounding the pulp Contains fewer numbers of tubules than primary Since it is formed after eruption, the odontoblasts slightly change direction which contributes to bending of dentinal tubules Usually a bending of tubules where primary and secondary dentin interface. The secondary dentin formed in greater amount especially in pulp chamber, roof & floor of pulp. Formed after root completion without any external stimuli. Has a regular arrangement. Secondary Dentin

34. Secondary Dentin Demarcation line Primary dentin

35. Tertiary dentin Reparative Dentin – formed to protect pulp irregularity of dentin varies with duration and intensity of stimuli. Sclerotic Dentin - Dentinal tubules get blocked because of calcium salt deposition . Formed to protect pulp , also seen as an age change. Formed after root completion because of external stimuli . Irregular in appearance & arrangement Produced in reaction to various stimuli Attrition, caries, or a restorative dental procedure Osteodentin – cells entrapped in tertiary dentin

36. Reparative dentin formed below the injured tubules. There are two types of reparative dentin Reactionary (from existing odontoblasts) Reparative (from differentiated odontoblasts)

37. Reactionary dentin appears as either osteodentin type or orthodentin type Histological difference between reactionary and reparative dentin is that reactionary dentin is deficient in acid proteins so it doesn’t stain. Reparative dentin has structure-less mineralisation as in bone.

38. Age & functional changes in dentin Odontoblasts and its processes are an integral part of dentin and so vitality is understood to be the capacity of the tissue to react to physiologic and pathologic stimuli ,dentin must be considered a vital tissue. Dentinogenesis is a process that continues through out life. Although after the teeth have erupted and have been functioning for a short time, dentinogenesis slows and further dentin formation is at a slower rate. This is secondary dentin Pathologic changes in dentin such as dental caries, abrasion, attrition or the cutting of dentin in operative procedures cause changes in dentin. They are the dead tracts, sclerosis and the addition of reparative dentin

39. DEAD TRACTS O bserved in ground section of tooth Due to death & loss of odontoblastic process Dentinal tubules becomes empty. These represents empty tubules filled with air appear black in transmitted light white in reflected light (seen in areas of loss of odontoblastic process due to caries, attrition , abrasion, erosion, cavity prep.)

40. Sclerotic Dentin Sclerotic dentin describes dentinal tubules that have become occluded with calcified material When this occurs in several tubules in the same area the dentin assumes a glassy appearance and becomes translucent Increases with age and is most common in the apical third of root and in the crown midway between the DEJ and surface of the pulp Because sclerosis reduces the permeability of dentin it may help to prolong pulp vitality Defensive reaction of dentin seen mainly elderly people.

41. Thought to be due to - Continued deposition of peritubular dentin Deposition of mineral within the dentinal tubules Mineralization of the odontoblastic process.

42. Reparative dentin It is a form of tertiary dentin. Noxious stimulus on the pulp . Differentiation of odontoblast from undifferentiated cells in the pulp Odontoblasts lay down a layer of dentin in the exposed area to protect the pulp from damage. Fewer & more twisted tubules than normal dentin. Dentin forming cells are usually trapped within the reparative dentin osteodentin

43. REPARATIVE DENTIN Dead tracts

44. Eburnated dentin Exposed , sclerotic dentin , where caries has been arrested and leaving smooth , darkened surface

45. Incremental lines / Von Ebner lines / Imbrication lines. Appears as fine line striation in dentin. Represent daily rhythmic deposition of dentin. Run at right angles to the dentinal tubules. The distance between incremental line is 4 to 8 mm in crown area less in root area. . seen mainly in longitudinal sections indicates growth pattern of dentin . Decrease mineralization .

46. Th e c o u rs e of t h e li n es i n d i ca t e the g ro w th pattern of the dentin Some of these incremental lines are accentuated because of disturbances in the matrix and remineralization process. Such lines are known as Contour lines of Owen These lines represent hypocalcified bands

47. In the deciduous teeth and in the first permanent molars, the prenatal and postnatal dentin is separated by an accentuated contour line, this is termed the Neonatal line . This line reflects the abrupt change in environment that occurs at birth The dentin matrix formed prior to birth is usually of better quality than that formed after birth

48. Incremental lines of von ebner Lines of owen Neonatal lines

49. Interglobular dentin Unmineralized or hypomineralized dentin where globular zones of mineralization have failed to fuse into a homogeneous mass within mature dentin. These zones are known as globular dentin or interglobular spaces Most frequently seen in circumpulpal dentin just below the mantle dentin. ( orban’s , oral histology , embryology and physiology ( 16 th edition )) Seen in dental anomlies (hypophosphatasia )

50. The dentinal tubules pass uninterruptedly, thus demonstrating a defect of mineralization and not of matrix formation

51. Tome’s granular layer Seen in root dentin adjacent to cementum seen in ground sections in transmitted light occurs due to coalescing and looping of terminal portions of dentinal tubules increases in amount from CEJ to root apex.

52. Innervation of Dentin contain numerous nerve endings in predentin and inner dentin no farther than 100- 150µm vesiculated nerve endings located within the tubules in coronal zone; especially in pulp horns These nerve endings are in close association with odontoblast process, within the tubules These may be single, multiple is believed that these terminal processes arise from myelinated nerve fibers of dental pulp. The primary afferent somatosensory nerves of the dentin and pulp project to the descending trigeminal nuclear complex ( subnucleus caudalis )

53. Theories of pain transmission through dentin Pain in general is defined by International Association for the study of Pain (IASP) as –  “ An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage. ” Pain is defined by  Monheim  as – “ an unpleasant emotional experience usually stimulated by a noxious stimulus and transmitted over a specialized neural network to the CNS where it is interpreted as such .”

54. There are 3 basic theories of pain conduction Direct neural stimulation Hydrodynamic theory Transduction theory

55.   Direct neural stimulation theory : According to this theory the pain stimuli reaches the nerve endings in the inner dentin. But how it reaches the nerve endings could not be explained. Due to little scientific proof it is not accepted now. Transduction theory :  According to this theory, the Odontoblastic processes are excited by the stimulus and transmit the impulses to the nerve endings. This theory is also of little importance as it has been noticed that there are no neurotransmitters in the dentin. Ref - Theories of pain transmission through Dentin August 18, 2008 by  Dr. Varun Pandula

56. Hydrodynamic theory : This theory is also known as ‘Fluid theory’, According to this theory the harmful stimuli such as heat, cold, air blast, mechanical pressure. . etc cause some changes in the fluid movement in the dentinal tubules either inwards or outwards which causes some mechanical disturbances due to mechanoreceptors present at the nerve endings, which stimulates the pain mechanism. The various types of pain are – Vague pain, Burning pain, Throbbing pain, Stabbing pain, Shooting pain (Trigeminal neuralgia). Theories of pain transmission through Dentin Ref - Theories of pain transmission through Dentin August 18, 2008 by  Dr. Varun Pandula

57. Direct neural stimulation proposed by Scott Stella in 1963. Drawbacks: The nerves in dentinal tubules are not commonly seen and even if they are present, they do not extend beyond the inner dentin Topical application of local anaesthetic agents do not abolish sensitivity Hence this theory is not accepted According to which nerves in the dentin get stimulated .

58. Transduction theory According to which the odontoblasts process is the primary structure excited by the stimulus and that the impulse is transmitted to the nerve endings in the inner dentin. Drawbacks: Since there are no neurotransmitter vesicles in the odontoblast process to facilitate the synapse or synaptic specialization

59. Hydrodynamic Theory Most popular theory Tubular nature of dentin permits fluid movement to occur Various stimuli such as heat, cold, air, mechanical pressure affect the fluid within the tubules; disturbing the free nerve endings which associated with odontoblast and its process nerve endings act as – mechanoreceptor as this affected by displacement of tubular fluid

60. Developmental disturbances Dentinogenesis imperfecta Dentin dysplasia Regional odontodysplasia Dentin hypocalcification

61. Dentinogenesis imperfecta is an autosomal dominant condition affecting both deciduous and permanent dentition Affected teeth are gray to yellowish brown and have broad crowns with constriction of cervical area resulting in a ‘tulip’ shape Radiographically teeth appear solid lacking pulp chambers and root canals Enamel is easily broken leading to exposure of dentin that undergoes accelerated attrition Dentinogenesis imperfecta

62. Clinical signs : Normal dentin formation is confined to the layer next to the enamel and cementum. Disordered dentin contains a few tubules. The roots of shell teeth and short. The primary teeth may be exfoliated prematurely. Teeth are characteristic reddish brown to grey opalescent color.

63. Radiographic appearance Partial/complete obliteration of pulp chamber , root canals Shell teeth- Normal Enamel, Thin Dentin, short roots

64. Prevention of loss of enamel & subsequent loss of dentin. Cast metal crowns on posterior teeth & porcelain jacket crown on anterior teeth are usually preferred Treatment

65. It is presence of normal enamel but a typical dentin with abnormal pulpal morphology. Dentin dysplasia There are two types Radicular coronal

66. Type I – (Radicular Dentin Dysplasia ) Both dentitions are affected & crowns appear clinically normal. Teeth exhibit mobility & are exfoliated prematurely. Roots are short, blunt, conical or malformed. Root canals are completely obliterated Dentin dysplasia type I – A rare entity Sangeeta Malik 1,, Swati Gupta 1, Vijay Wadhwan 1, GP Suhasini 1 PMC4451656  PMID: 26097326

67. Type – II (Coronal Dentin Dysplasia) Deciduous teeth have yellow, brown or bluish grey opalescent appearance. Pulp chambers of deciduous teeth are obliterated. Typical ‘Thistle tube’ appearance is seen in almost all teeth. Dentin dysplasia type I – A rare entity Sangeeta Malik 1,, Swati Gupta 1, Vijay Wadhwan 1, GP Suhasini 1 PMC4451656  PMID: 26097326 TREATMENT- No treatment Prognosis depends upon occurrence of periapical lesions necessitating tooth extractions

68. Regional odontodysplasia / or Ghost teeth It is an unusual anomaly which affects the localized area in unusual manner. maxillary anteriors are more commonly involved here. affects both dentitions. etiology of disease is unknown.. The teeth affected are showing delay or failure to eruption. The shape of teeth is altered, with irregular mineralization RADIOGRAPHIC FEATURES: “Ghost Teeth TREATMENT No treatment required • Meticulous oral hygiene • Extraction / Endodontic treatment • Prosthetic rehabilitation

69. Dentin hypocalcification Normal dentin is calcified by deposition of calcium salts in the organic matrix in the form of globules,which increase in size by peripheral deposition of salts until all the globules are finally united into a homogenous structure Failure of union of many of these globules results in dentin hypocalcification There is no alteration in clinical appearence DENS IN DENTE Dentin & enamel forming tissue invaginate the whole length of a tooth. Arises due to localised external pressure, focal growth retardation,focal growth stimulation in certain areas of tooth bud Pear shaped invagination Radiographically- “tooth within a tooth

70. Ref - Nakajima m , kunawarote , parasanuttiporn T , Tagani j. Bonding to caries affected dentin. Japenese dental science . Review (2011 aug 1 , 47 (2) ; 102 - 14

71. Caries – affected dentin produces lower bond strength & poor quality of the hybrid layer than normal dentin. Ref- Nakajima m , kunawarote , parasanuttiporn T , Tagani j. Bonding to caries affected dentin. Japenese dental science . Review (2011 aug 1 , 47 (2) ; 102 - 14

72. (According to Grossman, 1935) It is a commonly sensitive or painful response of exposed dentin to an irritation. Prevalence rate- 8.7 to 30 % of adult population. Dentinal Hypersensitivity

73. It has been stated in the literature that DH develops in two phases: lesion localization and lesion initiation Lesion localization occurs by loss of protective covering over the dentin, thereby exposing it to external environment. It includes loss of enamel via attrition, abrasion, erosion or abfraction. Another cause for lesion localization is gingival recession which can be due to toothbrush abrasion, pocket reduction surgery, tooth preparation for crown, excessive flossing or secondary to periodontal diseases. As stated earlier, not all exposed dentine is sensitive. For DH to occur, the lesion localization has to be initiated. It occurs after the protective covering of smear layer is removed, leading to exposure and opening of dentinal tubules. Ref - J Dent (Shiraz). 2013 Sep;14(3):136–145. Dentin Hypersensitivity: Etiology , Diagnosis and Treatment; A Literature Review AR Davari a, E Ataei a, H  Assarzadeh  b

74. MANAGEMENT OF HYPERSENSITIVITY Nerve desensitization Potassium nitrate Protein precipitation Gluteraldehyde Silver nitrate Zinc chloride Occluding dentinal tubules Sodium fluoride Stannous fluoride Strontium chloride Potassium oxalate Calcium carbonate Dentin adhesives Dentin bonding agents Composites Glass ionomers Crown placement lasers

75. Lasers used in the treatment of DH can be of two different types: low power lasers (LPL), such as Helium- Neonium (He-Ne) and Aluminum Gallium Arsenide ( AsGaAl ), high power lasers (HPL), such as the Neodymium Yttrium Aluminum Granate ( Nd:YAG ) and carbon dioxide (CO2) lasers7. Low intensity lasers, on the other hand, do not emit heat and present a low wavelength that stimulates the normality of cellular functions, acting in biostimulation due to the increased production of mitochondrial ATP, generating an increase in the excitability threshold of the free nerve endings that will result in actions with analgesic effect. REVIEW ARTICLE • BrJP 4 (2) • Apr-Jun 2021 • Treatment of dentin hypersensitivity with laser: systematic review Montes Claros, MG, Brazil.

76. Effect of operative procedures in dentin Heat produced during deep cavity preparation causes loss of odontoblasts or their aspiration into the dentinal tubules. Desiccation during cavity preparation has been long known to cause aspiration of odontoblastic nuclei into dentinal tubules.

77. Avoid Excessive cutting Heat generation Continous drying – dislodgement - aspiration into tubules use Air water coolant Sharp instruments

78. Dentin and Restorative Treatments It is well accepted that dentin is the best insulator for the pulp. Dentin must be treated with great care during restorative procedures to minimize damage to the odontoblasts and pulp. Air water spary should be used whenever cutting with high speed handpieces to avoid heat bulid up. The dentin should not be dehydrated by compressed air blasts.it should always maintain its normal fluid content .

79. Protection also is provided by judicious use of liners, bases ,dentin-bonding agents, and non toxic restorative materials. Restorations must seals the preparation adequately to avoid micro leakage and bacterial penetration. It is best to conserve as much sound tooth structure as possible and therefore the Remaining Dentin Thickness is the single most important factor in deciding the technique and materials of choice during restorative procedures

80. Based on the RDT the following pulp protective agent is placed before the final restorative material.

81. SMEAR LAYER AND SMEAR PLUGS Smear Layer term most often used to describe the grinding debris left on dentin by cavity preparation. This smear layer is only a few micrometres thick and is composed of denatured collagen, hydroxyapatite, and other cutting debris. The smear layer serves as a natural bandage over the cut dentinal surface because it occludes many of the dentinal tubules with debris called smear plugs .

82. The smear layer is a good protective barrier, it has a realtively weak attachment to the dentin and is subject to dissolution by acids. Smear layer is an amorphous, relatively smooth layer of microcrystalline debris with a featureless surfaces that cannot be seen with naked eye. (Pashley DH 1984)

83. Dentin Etching and Bonding Buonocore first brought about the concept of acid etching the tooth surface for better bonding. Although acid etched enamel showed great results, etched dentin which was air dried did not have positive results.

84. This solubilized phase when infiltrated with resin formed a layer that was neither dentin nor resin and was hence called as the ‘Hybrid Layer’ Bonding of resin to dentin using ‘total etch technique’ (Generation IV & V are based on this philosophy)

85. Scanning electron micrograph of etched dentin showing etched collagen fibers. Etched dentin showing exposed collagen fibers.

86. Vital Pulp Therapy The reparative Dentin Formation can be stimulated by cavity lining materials (such as Calcium hydroxide) (Ref -Surgical endodonticsJ.L . Gutmann, J.D. Regan, in Harty's Endodontics in Clinical Practice (Sixth Edition), 201)

87. Biodentine (Calcium Silicate Cement ) Composition: Contains tricalcium silicate, calcium carbonate, zirconium oxide, and additives to improve handling and reduce setting time. Setting Time : Rapid setting time of about 12 minutes. Applications: Pulp capping (direct and indirect). Apexification and apexogenesis . Repair of root perforations and resorption defects. Dentine replacement in restorations. Advantages: Easier handling and mixing. Quick setting and less technique-sensitive. Better esthetics compared to MTA due to no tooth discoloration. High biocompatibility and bioactivity, promoting dentin bridge formation. Drawbacks: Moderate radiopacity (less than MTA). Limited long-term clinical data compared to MTA. (Ref -Surgical endodonticsJ.L . Gutmann, J.D. Regan, in Harty's Endodontics in Clinical Practice (Sixth Edition), 201)

88. MTA ( Mineral trioxide aggregate) ) Composition - consists of a powder of fine trioxides (tricalcium oxide, silicon oxide, bismuth oxide) and other hydrophilic particles (tricalcium silicate, tricalcium aluminate, responsible for the chemical and physical properties of this aggregate). Setting Time: Takes 2–4 hours for initial set (depending on formulation). Applications: Pulp capping. Root-end filling material in endodontic surgeries. Apexification and treatment of immature teeth. Perforation and resorption repairs. Advantages: Excellent sealing properties. Superior radiopacity for radiographic evaluations. Proven long-term clinical success and biocompatibility. Drawbacks: Tooth discoloration (bismuth oxide). Difficult to handle and mix; sandy texture.Expensive compared to Biodentine . Long setting time. (Ref- Surgical endodonticsJ.L . Gutmann, J.D. Regan, in Harty's Endodontics in Clinical Practice (Sixth Edition), 201)

89. Clinical Preference- Biodentine - Preferred for restorative applications and situations requiring fast procedures. MTA : Ideal for endodontic surgeries and cases where high radiopacity is critical. (Surgical endodontics J.L. Gutmann, J.D. Regan, in Harty's Endodontics in Clinical Practice (Sixth Edition), 201)

90. Developmentally pulpal cells produce dentin, nerves and blood vessels. Although dentin and pulp have different structures, once they are formed, they react to stimuli as a functional unit. Exposure of dentin through attrition, caries or trauma produces profound pulpal reactions that tend to reduce permeability and stimulate formation of additional dentin. C ONC L US I ON

91. Orbans ’ Oral Histology and Embryology-G.S Kumar Pathways of the pulp- Cohen . Hargreaves- eleventh Edition. The art and science of Operative dentistry- Theodore Sturdevant- 5th Edition. RE FE RENCE S Orban’s oral histology and Embryology 10th edition Text book of dental and oral pathology, shafer- 4 th edition . Operative dentistry by Sturdevant 6th edition. Pathways of pulp, cohen 9 th edition.

92. THANK YOU