DENTIN
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Dentin is the hard, bony tissue found underneath the enamel of teeth. It is formed by odontoblast cells in a process called dentinogenesis, which occurs in two phases - organic matrix formation and mineralization. There are different types of dentin based on the time of formation (primary, secondary, tertiary) and relation to dentinal tubules (peritubular, intertubular, intratubular). Dentin contains dentinal tubules that contain odontoblast processes and nerves, and transmit sensations. Theories of dentin sensitivity include the direct nerve stimulation theory, transduction theory, and hydrodynamic theory which suggests that fluid pressure changes in dentinal tubules stimulate nerves to cause
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DENTIN
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- 2. Dentin By: Maaz Khan Ashfaq Azim Jawad Ullah Shah Gulzar Khan 2
- 3. CONTENTS • INTRODUCTION AND CHEMICAL COMPOSITION • DENTINOGENESIS • STRUCTURE OF DENTIN • TYPES OF DENTIN • INNERVATION OF DENTIN • THEORIES OF SENSITIVITY 3
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- 5. Introduction and Chemical composition • Dentin is a hard bone-like tissue that is present in the crown as well as in the root of teeth. • In the crown, dentin is covered by enamel and in the root it is covered by cementum • Unlike enamel, dentin is a vital tissue containing the cell processes of odontoblasts and neuron • Mature dentin has 20% organic, 70% inorganic and 10% water by weight . 5
- 6. • 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 6
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- 8. Dentinogenesis • The formation of dentin is called dentinogenesis, which starts before amelogenesis • Dentin is formed by odontoblast cells • Dentinogenesis takes place in two phases: 1. Organic Matrix Formation 2. Mineralization 8
- 9. Organic Matrix Formation • Odontoblasts then secrete matrix protein at the apical end of the cell and along its process • The secreted matrix is collagenous and not mineralized hence it is called predentin • As the matrix is being secreted the odontoblasts move towards the centre of the future pulp • The matrix that forms around the elongated cell process eventually 9 mineralizes and the odontoblastic process will lie within a dentinal tubule
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- 12. Contd… • As each day passes predentin is formed along the pulpal boundary, the adjacent predentin that was formed during the previous day mineralizes and becomes dentin • During the period of crown development approximately 4μm of dentin is laid down in every 24 hours • Incremental deposition and mineralization of dentine begins below the cusps, at the tips of the pulp horns at the DEJ • Dentinogenesis continues life long but slows down(1μm) , after the tooth is 12 completely erupted
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- 14. Mineralization • Early hydroxy apatite crystals deposition in form of fine plates on surface of collagen fibrils and ground substance • At first sites of calcification of dentine , crystal deposition appears to take place radially from common centre in a so called spherulite form • Factors controlling odontobalstic secretion and mineralization are not known 14
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- 16. • Key protiens secreted by odontoblasts that are involved in Dentinogenesis are; • Dentine phosphoprotien(DPP): binds to calcium and transports it to mineralization front • Osteonectin: inhibits growth of apatite crystal but promotes its binding to collagen matrix • Osteopontin: promotes mineralization • Gla-protein(gamma carboxy glutamic acid): act as nucleators to attract and concentrate calcium. 16
- 17. Cont’d… • Main genes involved in dentinogenesis are 1. MAP1B : For odontoblastic differentiation 2. PHEX: For dentin mineralization 17
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- 19. • General mineralization is slow • Peritubular region mineralizes at early stage • Ultimate crystal size is 3nm in thickness and 100 nm in length • Dentin-sialoprotien , in mineralizing dentin, affects the rate of mineral deposition 19
- 20. ASHFAQ AZIM ROLL NO: 07 20
- 21. Structure of Dentin • Main structure appreciated in an undermicroscope dentin are; 1. Structural lines 2. Dentinal tubules 3. Peritubular dentine 4. Intertubular dentine 5. Interglobular dentine 6. Tomes granular layer 21
- 22. 1.Structural lines • Formed due to the rhythmic alternating activity and rest period of dentin formation • The organic matrix of dentine is deposited incrementally at A daily rate of 4μm • Incremental lines run perpendicular to the dentinal tubules 22
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- 24. 3 types of structural lines are seen; 1. Incremental or imbrications' lines of von ebner 2. Contour lines of owen 3. Neonatal line 24
- 25. Incremental or imbrications' lines of von ebner INCREMENTAL LINES IN PERITUBULAR DENTIN OF THE TOOTH THAT CORRESPOND TO DAILY RATE OF DENTIN FORMATION 25
- 26. Contour lines of owen • Representing normal physiological alterations in the pattern of mineralization 26
- 27. Neonatal lines • Representing an exaggerated contour line of owen. • Neonatal lines are seen in all primary teeth and the first permanent molars 27
- 28. Dentinal tubules • Canal like branched structures extending from pulpal end to the dentino-enamel junction • Shallow s-shaped curvature (longitudionally) = PRIMARY CURVATURE • Undulations and wavy course along its length = SECONDARY CURVATURE • Lateral branches (1-2 microns) containing odontoblast processes. • Tubular population ranges from 15000/mm²(at DEJ) and 30000-75000/mm²(at pulpal region) • Contains: odontoblasts processes, non myelinted nerve fibres and dental lymph 28
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- 30. Peritubular dentine • Also called INTRA TUBULAR DENTINE • Hypermineralized dentin(40% more) surrounding the dentinal tubules • Formation continues throughout life at very slow rate which narrows the lumen of dentinal tubules leading to obliteration and results into formation of sclerotic dentine 30
- 31. Intertubular dentine • Dentin present between adjacent dentinal tubules • Less mineralized • Formed by the cell bodies of odontoblasts • Major organic component is collagen arranged in bundles perpendicular to D.Tubules 31
- 32. Interglobular dentine • Seen when mineralization of dentin begins in small globular areas that fail to coalesce into a homogenous mass. • It’s a mineralization defect • Generally star shaped with curved outlines of globular masses 32
- 33. CONT’D… • During section preparation organic matrix in interglobular proteins is lost and these areas get filled with air, appearing • Dark (under transmitted light) and • Bright(under reflected light) 33
- 34. Granular dentine • Also called as Tome’s Granular Layer • In longitudional section, peripheral layer of radicular dentin adjacent to cementum appears granular • Exact nature is not known 34
- 35. CONT’D… • Recent review shows that these granules represent true spaces created by extensive looping and coalescing terminal portions of dentinal tubules Appearing; • Dark (under transmitted light) and • Bright(under reflected light) 35
- 36. Predentin • Nonmineralized dentine • Present on pulpal surface • Comparable to osteoid of bone • 2-6 micron thick (maybe upto 20 microns) • Mineralizing front present throughout the life • Exists due to the mineralization lag • Act as covering of mineralized dentin and prevent resorbption 36
- 37. GULZAR KHAN ROLL NO: 72 37
- 38. Types of dentin On basis of Time of Formation 1. Primary Dentine 2. Secondary Dentine 3. Tertiary Dentine On Basis of Relation to Dentinal tubules 1. Peritubular Dentine 2. Intratubular Dentine 3. Intertubular Dentin Other types 1.Predentin 2. Interglobular Dentine 38
- 39. 1. Primary Dentin • Physiological dentin formed till root formation completion • Its of two types; A. Mantle dentin B. Circumpulpal dentin 39
- 40. A. Mantle dentine • First formed dentin • 20 microns in thickness • Derived from dental papilla and lacks phosphophoryn • Extends from dej upto zone of interglobular dentin • Contains large diameter collagen fibre 40
- 41. B. Circumpulpal dentin • Forms remaining part of primary dentine • Matrix with smaller diameter collagen fibres •Secreted by odontoblasts and contains phosphophoryn • More mineralized than mantle dentin 41
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- 43. 2. Secondary dentin • Physiological dentine formed after root completion • Formed throught out life • Continous formation reduces the size of pulp chamber 43
- 44. 3. Tertiary dentin • Also referred to as IRREGULAR SECONDARY DENTINE • Tertiary dentin can be reactionary or reparative • Reactionary dentin is that type of tertiary dentin that is deposited by the pre-existing odontoblasts • Reparative dentin is deposited by newly differentiated odontoblasts 44
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- 46. JAWAD ULLAH SHAH ROLL NO: 04 46
- 47. Innervation of dentin • Innervation throught intratubular nerves • Nerves accompany 30-70% odontoblastic process in close association with them 47
- 48. CONT’D… • It is believed most of these are terminal processes of the myelinated nerve fibres of the dental pulp • Primary afferent somatosensory nerves of the dentine and pulp project to the descending trigeminal nuclear complex 48
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- 50. 3 Theories of dentine sensitivity 1. Direct nerve stimulation 2. Transduction theory 3. Hydrodynamic theory 50
- 51. 1. Direct nerve stimulation • Nerves present in the dentinal tubules are reponsible Failure: • Extreme sensitivity • Marked sensitivity in pehripehral dentine • Sensitivity in newly erupted teeth 51
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- 53. 2. Transduction theory • Odontoblast act as receptor cells transmitting the impulse to pulpal nerves • Odontoblast origin from neural crest cells Failure: Experimental studies shows membrane potential of odontoblast was too low to permit conduction 53
- 54. 3. Hydro-dynamics theory • Nerves located in peripheral portion of pulp react to local changes are brought about by mechanical factors • When dentin is exposed , fluid( dental lymph) is lost • Hydrostatic equilibrium is disturbed in peripheral pulpal environment • Pressue changes stimulate nerves and initiate pain • Explains why local anesthetics doesnot reduce sentivity in dentin 54
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