Dentin

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1. DENTIN V.NIVEDHA First year MDS 14.07.2017

2. Contents : History Introduction Stages of tooth development Physical properties Composition Dentinal tubules Peritubular dentin Intertubular dentin Predentin Dentino -enamel junction Odontoblasts Primary denin

3. Contents Secondary dentin Tertiary dentin Incremental lines Interglobular dentin Granular layer Innervation of dentin Age and functional changes in dentin Dentinal fluid Clinical considerations Developmental disturbances New study,facts and evolution

4. HISTORY 1771 – John Hunter →hard tissue. 1775 – Anton Von Leeuwenhoek: Described tubular structures. 1837 -Purkinje and Retzius explained about Dentinal Tubules . Cuvien gave the name “Ivory” to Dentin 1867 – Neuman gave the term Neuman’s sheath 1891 – Von Ebner gave the term – Ebner’s growth lines or Imbrication lines . 1906 – Von Korff gave the term – Korff’s fibres

5. INTRODUCTION Second layer of the tooth Structure that provides the bulk and general form of the tooth Since it begins to form slightly before the enamel, it determines the shape of the crown, including the cusps and ridges and also the number and size of the roots.

6. Dentin  Physically and chemically, it closely resembles bone Said to be a living tissue since the tubules present in it contains processes of specialised cells, the odontoblasts . Main morphologic difference between bone and dentin is that some of the osteoblasts exists on the surface of the bone and when one of the cells becomes enclosed within its matrix, it is called an osteocyte

7. STAGES OF TOOTH DEVELOPMENT Teeth develop in distinct stages that are easily recognizable at the microscopic level. Hence, stages of tooth development ( odontogenesis ) are described by the histologic appearance of the tooth organ. The stages are described as the lamina bud, cap, early bell and late bell stages of tooth development

8. LAMINA STAGE First morphologic sign of tooth development Visible at approximately 6th week of human gestation. (embryo) At this stage, the cells in the dental epithelium and the underlying ectomesenchyme are dividing at different rates, the latter more rapidly

9. BUD STAGE The dental lamina continues to grow and thicken to form bud Cells of the ectomesenchyme and proliferate and condense to form the dental papilla . At this stage, the inductive or tooth forming potential is transferred from the dental epithelium to the dental papilla CAP STAGE The tooth bud assumes the shape of a cap that is surrounded by the dental papilla. Ectodermal compartment of the tooth organ is referred to as the dental or enamel organ.

10. EARLY BELL STAGE Dental organ assumes the shape of a bell as cells continue to divide but at differential rates. A single layer of cuboidal cells called the external or outer dental epithelium, lines the periphery of the dental organ Cells that border the dental papilla and are columnar in appearance form the internal or inner dental epithelium. The inner epithelium gives rise to the ameloblasts , cells responsible for enamel formation and outer enamel epithelium leads to the formation of mineralised dentin. These cells secrete high levels of alkaline phosphatase. In the region of the apical end of the tooth organ, the internal and external dental epithelial layers meet at a junction called the cervical loop. These extends apically to form the Hertwigs Epitheial root sheath which forms the root dentin

11. LATE BELL STAGE The dental lamina that connects the tooth organ to the oral epithelium gradually disintegrates at the late bell stage. Cells of the internal dental epithelium continue to divide at different rates to determine the precise shape of the crown

12. In summary, development of the tooth rudiment from the lamina to the late bell stages culminates in the formation of the tooth crown. As root formation proceeds, epithelial cells from the cervical loop proliferate apically and influence the differentiation of odontoblasts from the dental papilla as well as cementoblasts from the follicle mesenchyme. This leads to the deposition of root dentin and cementum .

13. PHYSICAL PROPERTIES Colour Young age - light yellow With advancing age - becomes darker Consistency Elastic and resilient Harder than bone but softer than enamel Tensile strength : 40mpa Compressive strength : 266mpa

14. COMPOSITION : Dentin has 35% organic, 65% inorganic and water by weight . The organic matrix of dentin is collagenous It provides resiliency to the crown which is necessary to withstand the forces of mastication The principle inorganic component of dentin is hydroxyapatite crystals The high mineral content of dentin makes it harder than bone and cementum but softer than enamel .The knoop hardness for dentin is approximately 68

15. Organic substances: 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) • Transforming growth factors β (TGF- β ) Inorganic substances: •Calcium hydroxy appatite crystals Type I collagen is the principal type of collagen found in dentine

16. DENTINAL TUBULES

17. The course of the dentinal tubules follow a gentle curve in the crown where it resembles an S shape Starts at right angles at the pulpal surface, the first convexity of this doubly curved course is directed towards the apex of the tooth  These tubules end perpendicular to the DEJ & CDJ It is almost straight near the root tip and along the incisal edges and cusps Dentin thickness ranges from 3-10mm or more Ratio btwn outer and inner surfaces of dentine is about 5:1 No. of tubules per square millimeter varies from 15000 at the DEJ to 65000 at the pulp – density and diameter increases with depth There are more tubules per unit area in the crown than in the root 

18. PERITUBULAR DENTIN The dentin that immediately surrounds the dentinal tubules is termed peritubular dentin Highly mineralised than intertubular dentin Twice as thick in outer dentin(approx. 0.75µm) than inner dentin(approx. 0.4µm) Calcified tubule wall has an inner organic lining termed the Lamina Limitans which is high in glucosaminoglycans

19. INTERTUBULAR DENTIN Located between the zones of peritubular dentin One half of its volume is organic matrix, specifically collagen fibres The fibrils range from 0.5-0.2µm in diameter and exhibit crossbanding at 64µm intervals  HA crystals are formed along the fibres with their long axis oriented parallel to the collagen fibres

20. Well mineralised , Provide tensile strength to dentin

21. PREDENTIN Located adjacent to the pulp tissues  2-6µm, depending on the activity of odontoblasts First formed dentin and is not mineralised The collagen fibres undergo mineralization at the predentin – the predentin then becomes dentin and a new layer of predentin forms circumpulpally

22. DENTINO ENAMEL JUNCTION The DEJ is a complex and critical structure uniting these two dissimilar calcified tissues and acts to prevent the propogation of cracks from enamel into dentin. The DEJ has a three level structure, 25-100 µm scallops with their convexities directed toward the dentin and concavities toward the enamel; 2-5 µm micro scallops and a smaller scale structure.

23. The convexities of the scallops are directed towards the dentin. The concavities are directed towards the enamel. The surface of the dentin at DEJ is pitted.

24. ODONTOBLASTIC PROCESSES Cytoplasmic extensions of the odontoblasts The odontoblasts reside in the peripheral pulp at the pulp- predentin border and their processes extend into the dentinal tubules The processes are largest in diameter near the pulp and taper further into dentin  The odontoblast cell bodies are approximately 7µm in diameter & 40µm in length 37

25. PRIMARY DENTIN Dentin that is formed prior to eruption of a tooth(before root completion) 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 major part of the dentin in the tooth TWO TYPES: MANTLE AND CIRCUMPULPAL

26. MANTLE DENTIN : Mantle dentin is the first formed dentin in the crown underlying the DEJ Regular in structure less mineralised and provides cushioning effect to the tooth It is the outer or most peripheral part of the primary dentin and is about 150µm thick

27. CIRCUMPULPAL DENTIN: Circumpupal dentin forms the remaining primary dentin or the bulk of the tooth The collagen fibrils are much smaller in diameter and are more closely packed together Slightly more mineral content than in mantle dentin

28. SECONDARY DENTIN Formed after root completion Narrow band of dentin bordering the pulp Contains fewer tubules than primary dentin There is usually a bend in the tubules where primary and secondary dentin interface Appears in greater amounts on the roof and floor of the pulp where it protects the pulp from exposure in older teeth

29. TERTIARY DENTIN Localized formation of Dentin At pulp –Dentin Border in response to noxious stimuli- Caries, Trauma Attrition , Cavity Prep. Etc. Also known as: Reactive Dentin, Reparative Dentin , Irritation Dentin , Replacement Dentin, Adventitious Dentin, Defense Dentin T here is ↓ Dentin permeability . Quality Depends on : •Intensity of stimulus. •Vitality of pulp.

30. INCREMENTAL LINES The incremental lines of Von Ebner or imbrications lines appear as fine lines or striations in dentin Run at right angles to the dentinal tubules. The course of the lines indicates the growth pattern of the dentin These lines reflect the daily rhythmic, recurrent deposition of dentin matrix

31. 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

32. 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 . INTERGLOBULAR DENTIN Sometimes mineralization of dentin begins in small globular areas that fail to fuse into a homogenous mass. This results in zones of hypomineralisation btwn the globules . These zones are called interglobular dentin. Forms in crowns of teeth in the circumpulpal dentin just below the mantle dentin

33. GRANULAR LAYER There is a zone adjacent to the cementum that appears granular known as Tome’s granular layer It slightly increases in amount from the CEJ to the root apex Caused by coalescing and looping of the terminal portions of the dentinal tubules Highest concentration of calcium and phosphorous

34. INNERVATION OF DENTIN Nerve fibres were shown to accompany 30-70% of the odontoblastic process and these are referred to as intratubular nerves These nerves and their terminals are found in close association with the odontoblasts process within the tubule THEORIES Direct neural stimulation Transduction theory Modulation theory “Gate” control / Vibration theory Hydrodynamic theory

35. DIRECT NEURAL STIMULATION According to which nerves in the dentin get stimulated . 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 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

36. HYDRODYNAMIC THEORY Most accepted theory Various stimuli such as heat, cold, airblast dessication or mechanical or osmotic pressure affect fluid movement in the dentinal tubules. This fluid movement either inward or outward, stimulates the pain mechanism in the tubules by mechanical disturbance of the nerves closely associated with the odontoblast and its process Thus these endings may act as mechanoreceptos as they are affected by mechanical displacement of tubular fluid

37. AGE AND FUNCTIONAL CHANGES IN DENTIN Vitality of 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

38. REPARATIVE DENTIN By pathologic process or operative procedures, the odontoblastic processes are exposed or cut, the odontoblasts die or survive, depending on the extend of injury If they survive, dentin that is produced are called reactionary or regenerated dentin Killed odontoblasts are replaced by the migration of undifferentiated cells arising in the deeper layers of the pulp to the dentin interface This newly differentiated odontoblasts then begin deposition of reparative dentin to seal off the zone of injury as a healing process initiated by the pulp,  Resulting in resolution of the inflammatory process and removal of dead cells

39. This type dentin produced by a new generation of odontoblast -like cells in response to appropriate stimulus after the death of original odontoblasts is called Reparative dentin This reparative dentin has fewer and more twisted tubules than normal dentin Histological difference between reactionary and reparative dentin is that reactionary dentin is deficient in acid proteins so it doesn’t stain. Reactionary dentin appears as either osteodentin type or orthodentin type Reparative dentin has structure-less mineralisation as in bone.

40. SCLEROTIC DENTIN Presence of irritating stimuli -Caries, Attrition, Erosion, Cavity Preparation → Deposition of Apatite Crystals & Collagen in Dentinal Tubules. Blocking of tubules- Defensive reaction. Filled with H. A - Obliteration of Lumen- Peritubular Dentin. Refractive indices are equalized- Transparent Elderly people – Mostly in Roots Also seen- slowly progressing Caries . Reduced Permeability Prolonged pulp vitality Resistant to Caries

41. DENTINAL FLUID Free fluid occupies 1% of superficial dentin and 22% of total volume of deep dentin Ultrafiltrate of blood from pulp capillaries Contains plasma proteins Serve as a sink from which injurious agents can diffuse into the pulp producing inflammatory response Also serve as a vehicle for egress of bacteria from a necrotic pulp into periradicular tissue

42. CLINICAL CONSIDERATIONS:

43. “Exposure of Dentinal Tubules ” Tooth wear, fractures, caries, cavity cutting procedures etc. lead to exposure of Dentinal tubules. 1 mm of Exposed Dentin → Damage to 30,000 living odontoblasts . Exposed Tubules- Should not be insulted!! Sealed- Bonding agents, varnishes or Restorations .

44. PULP PROTECTION Irritants from Restorative Materials- Pulpal Damage • Thermal Protection- Bases below Restoration on Dentin • Chemical Protection- Cavity liners and varnishes

45. HYPERSENSITIVITY Unusual symptom of Pulp- Dentin Complex. Sharp Pain- easily localized. Etiology- Exposure of Dentinal tubules loss of enamel- Attrition, abrasion, erosion etc. loss of cementum - scaling and RP, Gingival Recession Best Explained by the Hydrodynamic Theory. Management - Block The Dentinal Tubules!!! • Desensitising toothpastes-AgNo3, SrCl2, fluorides, Bonding Agents, lasers etc.

46. SMEAR LAYER AND SMEAR PLUGS Smear Layer - term most often used to describe the grinding debris left on dentin by cavity preparation Cutting debris when forced into dentinal tubules, it forms plugs known as smear plugs Smear layer : 1-3 µm  Smear plug : 40 µm  Significance - Lowers the permeability of dentin surface and occludes it Disadvantage: prevents the adhesion of restorative materials in the dentin

47. DENTAL CARIES Due to increased Permeability of dentin by tubules,it acts as a pathway of various kinds of micro organisms Rapid spread of Caries Through Dentin ZONE 1 – Normal dentin ZONE 2 – Sub transparent ZONE 3 – Transparent dentin ZONE 4 – Turbid dentin ZONE 5 – Infected dentin

48. INFECTED DENTIN AND AFFECTED DENTIN Infected dentin is that part of dentin which is contaminated and contains the microorganism with their toxins, and demineraliaed dentin. Brownish black in colour Can be scooped off Should be removed Affected dentin is not occupied by microorganism it just contains the toxins produced by microorganisms of the infected dentin, and also there is demineralization. Light brown in colour Cannot be scooped off Not necessary to remove completely Have a chance of remineralisation

49. OPERATIVE INSTRUMENTATION • AVOID- Excessive Cutting Heat Generation Continuous Drying • USE : Air- Water Coolant. Sharp hand Instruments- most suitable Tungsten Carbide Burs to Cut vital Dentin,Less Heat generation. Dentin- Treated with care during op. instrumentation to prevent damage to the odontoblasts

50. CAVITY PREPARATION Cavity Floor → Dentin Dentin is RESILIENT → Absorbs and Resists Forces of Mastication and deformation – Grips the rest. material. BOUNCE BACK EFFECT Grooves, coves, pins etc – completely in Dentin .

51. VITAL PULP THERAPY The reparative Dentin Formation can be stimulated by cavity lining materials (such as Calcium hydroxide ) Materials like Mta,Biodentine - can be used as a substitute to dentin(capable of inducing reactionary dentin by stimulating odontoblastic activity and repairative dentin by induction of cell differentian ) Includes Direct and Indirect pulp capping • Results in formation of reparative dentin . THE DENTINAL BRIDGE repair tissue that forms across the pulpal wound. Sign of successful healing.

52. ENDODONTICS Secondary & Tertiary Dentin →obliteration of Pulp Chamber & Root Canals. Endodontic treatment → Difficult. Apical Dentin Chip Plug- Dentinal Chips compacted at apex during Obturation - provides a “biologic seal ”

53. ENDODONTIC SURGERY All isthmus must be found,prepared and filled during surgery Pic A-reverse filling does not extend coronally to the height of the bevel,arrows indicate a possible pathway for fluid penetration

54. P ic B - reverse filling extends coronally to the height of the bevel blocking fluid penetration into the root canal space Significant removal of the isthmus and proper restoration have significantly reduced the failure of endodontic surgeries

55. Ellis classification (Tooth fractures) Ellis Class I Enamel fracture: This level of injury includes crown fractures that extend through the enamel only. These teeth are usually nontender and without visible color change but have rough edges. Ellis Class II Enamel and dentin fracture without pulp exposure: Injuries in this category are fractures that involve the enamel as well as the dentin layer. These teeth are typically tender to the touch and to air exposure. A yellow layer of dentin may be visible on examination.

56. Ellis Class III Crown fracture with pulp exposure: These fractures involve the enamel, dentin, and pulp layers. These teeth are tender (similar to those in the Ellis II category) and have a visible area of pink, red, or even blood at the center of the tooth. Ellis Class IV Traumatized tooth that has become non-vital with or without loss of tooth structure. Ellis Class V Luxation: The effect on the tooth that tends to dislocate the tooth from the alveolus. Teeth loss due to trauma. Ellis Class VI Fracture of root with or without loss of crown structure.

57. Ellis Class VII Displacement of a tooth without the fracture of crown or root. Ellis Class VIII Fracture of the crown en masse and its replacement. Ellis Class IX Fracture of deciduous teeth.

58. TREATMENT OF CLASS II ELLIS Simple restorations

59. PIGMENTATION: Tetracycline Pigmentation Yellow- Brown/grey Discoloration. Fluoresce Bright Yellow under U.V light. Deposited along Incremental lines of Dentin and to lesser Extent in Enamel.

60. BEVELS: Bevels are angulations which is made by 2 surfaces of a prepared tooth which is other than 90 degrees. They are created to increase the retention and to prevent marginal leakage Hey are given at various angulations depending upon the type of material used for restoration and the purpose the material serves

61. CHEMICAL AGENTS : Sterilization and disinfecting chemicals applied to the dentin produce odontoblastic injury Alcohol &chloroform produce thermal irritation by evaporation and dehydrate dentinal tubules Hydrogen peroxide may travel through dentinal tubules of deep cavity preparations and into the pulp producing emboli and perhaps even arresting circulation.

62. DENTIN CONDITIONING AGENTS : C lassic acid etchant used on dentin de mineralize Peritubular dentin which widens the tubule increasing permeability. The acid should be passively applied for short periods 5-15 secs This technique leaves behind smear plugs in tubule apertures The intact collagen framework interacts with hydrophilic priming agents which penetrate through the remnant smear layer and into the Intertubular dentin and fills the spaces left by the dissolved apatite crystals. This allows acrylic monomers to form an interpenetrating network around dentin collagen.

63. BONDING ON DENTIN: Adhesive resin of the dentin bonding agent micromechanically interlocks within the inter tubular dentin and surrounding collagen fibers Hybrid layer is formed in following manner:- 1.etching removes smear layer and exposes collagen fibers . It also removes hydroxy apetite with in the intertubular dentin 2 . Primers penetrate the collagen network. 3.Adhesive resins along with the primers form resin microtags within the intertubular dentin . Hybrid layer is also called resin-dentin interpenetration/ interdiffusion zone

64. A MICROSCOPICAL VIEW When dentin is cut, the inorganic hydroxyapatite crystals are broken up and the collagen is stretched, torn, and smeared over the cut surface.  The above picture shows how a cut dentin surface is covered with such a "smear layer."

65. This picture shows how the smear layer covers the dentin and form so called "smear plugs."  Before any serious bonding attempt can be made, this "smear" layer must be removed. Such a removal is achieved with a so-called "conditioner." In most cases, the conditioner consists of an acid .

66. Dentin should be etched for 15 - 30 s. During this time, the smear layer is removed and the outer surface of the dentin is demineralized leaving a demineralized collagen mesh, attached to the mineralized dentin located a few microns under the collagen surfaces.   The above figure shows how the dentin surface looks after it has been etched for 15 s.

67. As long as this collagen mesh remains moist, it is fluffy. However, if it is desiccated, the mesh structure densifies .  Fortunately, it is possible to re-swell the mesh by rubbing the surface with a water-saturated pellet. In order to infiltrate the moist collagen mesh with a primer, one must use a primer that consists of a molecule that has both a hydrophilic and a hydrophobic end

68. DENTIN DESSICATION AND ASPIRATED ODONTOBLASTS 1n the absence of a water spray,coolant,tooth reduction incurs not only the risk of heat trauma but , also , of desiccation of the dentin and aspiration of odonto - blasts into the dentinal tubu1es.These effects followed an air-cooled cavity prepara - tion and the prolonged application of an air blast . Frictional heat generated dur - ing tooth reduction causes evaporation and expansion of the tissue fluid in dentin . These phenomena suggest a loss of tissue fluid at the surface of exposed dentin and an outward capillary flo w .~ Any strong dehydrating agent may produce the same effect.A dry cavity preparation lasting only a few seconds

69. or an air blast of more than 20 seconds may induce aspiration of cells into the tubules . Odontoblasts aspirated through exposure to an air blast disappears within 24 hours by autolysis and further outward displacement The dissolution of aspirated cells does not cause inflammation of the pulp or injure the cells in the cell rich zone A reduction in the number of odontoblasts leads to the formation of repairatve dentin after 1 -3 months

70. RESTORATIVE MATERIALS: A restoration placed in a cavity preparation can develop contraction gaps between the restoration and the cavity wall. This gap then fills with fluid from the outflow of tubules or saliva from external surface. An environment is created for bacterial growth and failure of restoration .

71. DEVELOPMENTAL DEFECTS

72. DENTINOGENESIS IMPERFECTA Anomaly of Mesodermal Portion of the Odontogenic Apparatus . TYPE I - Assoc with. O.I TYPE II - Not Assoc with O.I TYPE III - Brandy wine Type CLINICAL FEATURES Tulip Shaped teeth, Bluish- grey- Yellow/Brown Translucent . Enamel Chips away→ Exposed dentin, rapid attrition . Amber appearance, Excessive wear, Multiple pulp Exposures.

73. RADIOGRAPHIC FEATURES Partial/complete obliteration of pulp chamber , root canals Shell teeth- Normal Enamel, Thin Dentin , short roots.

74. TREATMENT In patient with DI, one must first be certain which type he/she are dealing with. Severe cases of DI type 1 associated Osteogenesis imperfecta can present significant medical management problems. Careful review of the patient's medical history will provide clues as to the severity of bone fragility based on the number of previous fractures and which bones were involved. Patients not exhibiting enamel fracturing and rapid wear crown placement and routine restorative techniques may be used. Bonding of veneers may be used to improve the esthetics.

75. In more severe cases, where there is significant enamel fracturing and rapid dental wear, the treatment of choice is full coverage crowns. However in case of D.I III with thin root are not good cases for full coverage because of cervical fractures. Occlusal wear with loss of vertical dimension – Metal castings Newer composites.

76. DENTIN DYSPLASIA(ROOTLESS TEETH) Rare Dental Anomaly Normal Enamel, Atypical Dentin, Abnormal Pulp Morphology CLASSIFICATION : (Acc. To WHITKOP) – TYPE I- RADICULAR TYPE II – CORONAL

77. TYPE I(RADICULAR) TYPE II (CORONAL) CLINICAL FEATURES Normal Morphology, Amber Translucency. Extreme Mobility and Premature Exfoliation Primary- yellow /brown- grey. RADIOGRAPHIC FEATURES Deciduous - pulp chambers completely obliterated, short conical roots. Permanent – crescent shaped pulp chambers- Difficulty in locating canal orifices.Permanent - “thistle tube” appearance

78. HISTOLOGIC FEATURES: Calcified / atubular dentin Lava flowing around boulders pattern is seen Amorphous forms and cascades of dentin

79. TREATMENT No treatment If periapical pathology arises extraction is advised

80. REGIONAL ODONTODYSPLASIA Usually seen in Maxillary Anteriors CLINICAL FEATURES: unusually large pulp chambers with thin layers of enamel and dentin are evident.delay or failure of eruption, irregular shape. RADIOGRAPHIC FEATURES : “Ghost Teeth.”

81. HISTOLOGIC FEATURES: Reduction in amount of dentin Widening of pre-dentin layer Presence of large interglobular dentin Irregular tubular pattern of dentin TREATMENT No treatment required • Meticulous oral hygiene • Extraction / Endodontic treatment • Prosthetic rehabilitation

82. DENS IN DENTE Dentin & enamel forming tissue invaginate the whole length of a tooth. Arises due to localised external pressure, focalgrowth retardation,focal growth stimulation in certain areas of tooth bud Pear shaped invagination Radiographically - “ tooth within a tooth.”

83. Food lodges in the cavity to cause caries which rapidly penetrates the distorted pulp chamber Endodontic Treatment Difficult- abnormal Anatomy

84. NEW STUDY!!!!!

85. NEW CONCEPT TO REGENERATE TOOTH STRUCTURES Need for fillings could be reduced in future as study reveals natural ability of teeth to repair themselves can be enhanced using Alzheimer’s drug The activation of stem cells in the centre of teeth works to repair small cracks and holes in dentine. Enhancing this ability could allow the tooth’s own cells to rebuild cavities . Dentists have devised a treatment to regenerate rotten teeth that could substantially reduce the need for fillings in the future . The therapy works by enhancing the natural ability of teeth to repair themselves through the activation of stem cells in the soft pulp at the centre .

86. Prof Paul Sharpe, is leading the work at King’s College London, “Almost In the trial, in mice, the team showed that when defects were filled with a biodegradable sponge soaked in the drug, the tooth was gradually able to rebuild itself . Restoring the tooth’s original dentine structure is preferable because dental cements used in conventional fillings weaken the tooth, leave it prone to future infections – and inevitably erode or detach The new treatment would not eliminate the need for the dentist’s drill, however, since decaying sections of the tooth would still need to be removed .. The therapy relies on a drug called tideglusib , which has been assessed as a potential Alzheimer’s treatment, and which is known to be safe for clinical use .

87. the drug stimulates stem cells in the centre of the tooth, triggering them to develop into odontoblasts ( specialised tooth cells) and boosting the production of dentine, allowing larger defects to be reversed.. In the study, published in Scientific Reports, the scientists drilled holes into the teeth of mice, inserted a biodegradable collagen sponge soaked in the drug and sealed the tooth with a dental adhesive. When the teeth were examined several weeks later, the sponge had degraded and been replaced with new dentine. Collagen sponges are commercially available and clinically-approved. The dental preparation of the tooth would be almost identical to that required for conventional fillings, according to the scientists.

88. A remaining question is whether the method will scale up successfully to human teeth, in which cavities can be significantly larger. The team are currently testing the technique in rats, whose teeth are about four times larger than those of mice, and if this is successful plan to apply later this year to carry out the first clinical trials in patients.

89. FACTS ON DENTIN Elephant ivory is solid dentin. The structure of the dentinal tubules contributes to both its porosity and its elasticity . Elephant tusks are formed with a thin cap of enamel, which soon wears away, leaving the dentin exposed. Exposed dentin in humans causes the symptom of sensitive teeth . Because dentin is softer than enamel, it wears away more quickly than enamel. Some mammalian teeth exploit this phenomenon, especially herbivores such as horses , deer or elephants . In many herbivores, the occlusal (biting) surface of the tooth is composed of alternating areas of dentin and enamel. Differential wearing causes sharp ridges of enamel to be formed on the surface of the tooth (typically a molar ), and to remain during the working life of the tooth. Herbivores grind their molars together as they chew ( masticate ), and the ridges help to shred tough plant material. A material similar to dentin forms the hard material that makes up dermal denticles in sharks and other cartilaginous fish

90. REFERENCES Orbans ’ Oral Histology and Embryology-G.S Kumar – Twelfth Edition Pathways of the pulp- Cohen. Hargreaves- eleventh Edition. Shafer’s Textbook of Oral Pathology- Shafer , The art and science of Operative dentistry- Theodore Sturdevant - 4th Edition.

91. The effect of dentin desiccation and aspirated odontoblasts on the pulp M.brannstrom,odont.dr SUMMITS fundamentals of operative dentistry 4 th edition