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Dentine (Physical Properties (Permeable (Depending on size and patency of…

- - - - Mineral content decreases
      - Thickness of crystals increases
      - Hardness decreases
      - Elastic modulus decreases
  - - - Slightly (~5%) less mineralized
      - Collagen fibres are oriented perpendicular to DEJ
        
        And hence can be distinguished from circumpulpal dentine beneath using polarized light
      - Dentinal tubules branch profusely
      - Undergoes mineralization in the presence of matrix vesicles
    - - Low tubular density
      - Very thin
      - Some extend into the enamel as enamel spindles
  - - - Width depends on the rate at which dentine is being deposited
        
        Thicker in young teeth
  - - - Outermost later of root dentine
      - Narrow (< 20μm), non-tubuar structureless clear band
        
        Because odontoblatss do not leave behind an odontoblast process in the initial few microns of tissue
      - Blends with collagen fibres from cementum and serves to bond cementum to dentine
      - CDJ and cementum may distribute occlusal stress so that they do not concentrate in the PDL
    - - Hypomineralized compared to circumpulpal dentine
      - Layer immediateely beneath the hyaline layer in the periphery of the root dentine
      - Narrow, dark zone
      - Visible only in ground section
      - Formed because dentinal tubules in this area branch more profusely and loop back on themselves
        
        Creates air spaces that result in internal reflection of transmitted light
      - Differences in the rate of formation of crown and root dentine explain why it is only visible in the root
  - - - Outer part of circumpulpal dentine beneath mantle layer, and beneath granular layer in root
        
        Separates mantle and circumpulpal dentine
      - Often incompletely mineralized/ calcified
        
        Incomplete fusion of calcospherites, globules of HAP
        
        In other areas, the calcospherites fuse to form uniformly calcified tissue
        
        Uncalcified, interglobular layers appear dark when ground sections are views in transmitted light
      - Peritubular dentine is absent from tubules as they pass through
      - Dentinal tubules pass without deviation through interglobular layers
    - - Peripherally: separated from mantle layer by interglobular dentine which marks incomplete initial mineralization
      - Centrally: mineralizing front represents ongoing mineralization
- - - - Consist of small parallel tubules in a mineralised collagen matrix
  - - - Cell bodies of odontoblasts line the deep surface of dentine and define the outer border of dental pulp
  - - - Increases in thickness at the expense of dental pulp
      - Evidence: presence of unmineralized layer of dentine matrix @ pulpal surface known as predentine
- - - - Collagen fibrils run parallel to pulpal surface / transverse to dentinal tubules
      - CFs of mineralized dentine are of larger diameter and more closely packed than predentine
      - CFs are not assembled in bundles
    - - Some Type II and V
      - Provide elasticity
  - - - Dentine Phosphoproteins
        
        Refers to highly phosphorylated protein species
        
        High phosphate content = super acidic
        
        High calcium ion binding properties
        
        Involved in mineralization
        
        main non-collagenous protein
        
        Dentine Sialoprotein (DSP), Dentine phosphoprotein (DPP)
      - Bone Sialoprotein (BSP)
      - Dentine Matrix Protein-1 (DMP-1)
      - Matrix extracellular protein phosphoglycoprotein
    - - Significant component of non-collegenous proteins
      - In dentine, represented by smaller molecular weight type proteins
        
        E.g. decorin, biglycan
      - GAGs are primary chondroitin-4-suphate and chondroitin-6-sulphate
      - Function
        
        Collagen fibril assembly
        
        Cell-mediated effects
        
        Cell adhesion, migration, proliferation & differentiation
        
        Mineralization
        
        Bind calcium non-specifically
    - - Present in low amounts
      - Bind strongly but reversibly to HAP crystallites
      - May play a role in mineralization
    - - Osteonectin
        
        High levels of glutamic and aspartic acid
        
        Makes up 5% of total protein
      - Osteopontin
        
        phosphorylated glycoprotein
        
        in predentine
      - Osteocalcin
    - - Functions
        
        Form bone matrix
        
        Absorb circulating tissue fluid
        
        Regulate dentogenesis
        
        Regulate tooth development
      - Released during trauma or disease
    - - Functions
        
        Development, Homeostasis, Repair
      - EDTA, Ca(OH)2, Mineral Trioxide Aggregate (MTA) solubilise dentine matrix proteins (DMP) and release signalling molecules that influence dentine repair and regeneration
      - Acids release matrix signalling molecules that influence cellular events for dentine repair and regeneration
    - - DPP plays impt role
      - First layer of dentine matrix is unmineralised
        
        Mineralization occurs when it reaches a certain width
        
        Progresses at same rate as matrix formation
      - Odontoblasts initate and control mineralization
      - Matrix Vesicles initiate initial mineralization in mantle dentine
        
        They bud off as odontoblasts retreat
        
        Contain high local conc. of Ca2+ and PO43- required for calcification
        
        Contains alkaline phosphatase which liberates phosphate ions from organic phosphate
      - Mineral phase begins with matrix vesicles as single crystals
        
        Crystals grow and break through vesicle membrane to form spherical foci of HAP known as calcospherites
        
        Calcospherites grow and fuse to form the mineralization front (globular calcification)
        
        More common in mantle dentine but occurs throughout
        
        When rate of formation is more uniform and progresses linerarly, it is linear calcification
        
        (def.) Calcospherites are spherical foci of HAP formed from calcium phosphate nucleating sites which eventully fuse to firm the mineralization front
- - - - Starts of perpendicular to pulpal surface and convexity of primary curvature nearest pulp chamber faces rootwards
      - In root/ beneath cusps, primary curvature are less pronounced and straighter
      - Also show small changes in direction aka secondary curvatures
        
        Coinciding secondary curvatures of adjacent tubules may give rise to appearance of contour line of Owen
        
        Common at the junction of primary and secondary dentine, where odontoblasts seem to simultaneously change direction during formation
      - Curvature results from crowding of odontoblasts as they retreat towards centre of pulp
    - - 2.5 μm diameter @ pulpal end
      - ~1 μm peripherally
    - - Bc during formation odontoblasts migrate inwards and occupy smaller surface area
      - Tubules account for 22% of cross sectional area near pulp but only 2.5% near DEJ
    - - More profuse @ periphery near DEJ
        
        Due to the numerous processes the early odontoblasts has
      - Some small side branches
        
        end blindly
        
        unite with branches of other tubules
      - In root, terminal tubule branches and branches loop
        
        Gives rise to appearance of granular layers of Tomes
      - In dentine beneath periphery, branching is not obvious
      - In uncalcified predentine, branching is more notable
        
        During mineralization many odontoblastic branches retract and the small canals they occupied fill in
    - - Decreases from pulp (2-3μm) to CEJ and DEJ (1μm)
      - Narrowing is due to development of peritubular dentine on walls of tubules in outer part of dentine
    - - Decreases from pulp to DEJ
      - Tubules more widely separated at periphery because during tubule formation, odontoblasts occupy a smaller SA as they migrate inwards
  - - - Found throughout dentinal matrix except in areas of interglobular and hyaline dentine and tubules near pulp
    - - Lacks collegenous fibrous matrix
        
        Causes it to be lost if dentine is routinely demineralized
      - Higher radiographic and electron density
      - 5-12% more mineralized than ITD
      - Carbonated apatite crystals are smaller and 5X harder than ITD
    - - With physiological ageing, tubules can become fully occluded to become translucent dentine
      - Occupies 2/3 of SA near pulp but only 3% near DEJ
    - - High mineral content and small crystals increase mechanical properties and durability
      - Highly fenestrated pores enable flux of fluids and ions
- - - - Deeper cavity --> More porous dentine --> more prone to bacteria entering pulp --> enhanced caries spread
    - - Exposure of dentine surface to caries, attrition, abrasion, trauma
      - Patency of tubules
        
        Tubules may be occluded physiologically by peritubular dentine (translucent dentine)
        
        Exogenous materials may precipitate in tubules (sclerotic dentine)
        
        May be sealed off from pulp by tertiary dentine
      - Outward movement of dentinal fluid washing them out of tubule
      - Ability to pass through odontoblast later which present a barrier to molecules of higher weight
  - - - Advantage: occludes the dentinal tubules and blocks tubules in sclerotic and translucent dentine
      - Disadvantage: may harbour bacteria and provide a difficult surface to adhere to
      - Must remove smear layer before applying bonding agent (by using strong acid)
        
        This provides a poroud surface that can be infiltrated by the bonding agent which will penetrate dentinal tubules
- - - - Formed by coincidences between peaks of signmoid primary curvature
      - Seen as
        
        Broad bands in longitudinal section
        
        Broad concentric bands in transverse secrion
      - Comparable to Hunter Schreger band in enamel
    - - Formed by coincidence of secondary curvatures
      - A pronounced line of owen is found at the border of primary and secondary dentine where there is an abrupt change in dentinal tubule direction
  - - - Short period markings showing alternating dark (mineralized) and light bands
      - Perpendicular to dentinal tubules
      - Bands lie approximately 3μm apart
        
        4μm in cuspal dentine where deposition is most rapid
        
        2μm in root near granular layer where dentine is calcospheritic pattern
      - Comparable to cross striations in enamel
      - Reflects diurnal rhythm of dentine formation
    - - Mark the pattern of dentinogenesis
      - Are formed due to
        
        Circadian fluctuations in acid-base balance that affect both mineral content and refractive index of the forming hard tissue
        
        Changes in collagen fibrli orientation
    - - Long period lines which are coarser
      - Associated with changes in collagen fibril orientation
      - Perpendicular to dentinal tubules
      - Comparable to Retzius lines in enamel
      - Lines lie 20-30μm apart, with 6-10 pairs of short period markings between 2 Andreson lines
      - Reflects weekly rhythm of dentin formation
    - - Accentuated contour line separating prenatal and postnatal dentine
      - Includes compositional variations in matrix and mineralization: reflects abrupt changes in enviornment
      - Seen in primary teeth and first permanent molars
- - - - Structurally similar to primary dentine
        
        Regular circumpulpal dentine formed in continuity with primary dentine, but at a slower rate
        
        Tubules formed are continuous with primary dentine
        
        BUT they are often delineated (can be distinguished) as a result of a change in direction of dentinal tubulewith coincidence of secondary curvature, producing a pronounced contour line of Owen
      - Produced by downregulated odontoblasts
        
        after tooth goes into occlusion
        
        after completion of root formation
      - Rate of secondary dentin deposition is generally slower than the rate of primary dentine deposition
        
        Together with increased crowding of odontoblasts, this leads to tubular pattern of secondary dentine being less regular, and incremental markings being closer together
      - Greater deposition on roof and floor of pulp chamber where occlusal forces are higher
        
        stimuli for secondary dentine deposition is higher
      - Continuous deposition leads to
        
        smaller pulp chamber
        
        Narrower root canal
        
        More difficult to locate root canal
    - - In physiological ageing, tubules can be completely occluded with peritubular dentine (whitlock crystals) to form translucent dentine
      - Starts with apical portion of root and progresses coronally
      - Translucent dentine increases linearly with age
        
        Can be used in forensic science to determine age
      - More prone to fracture compared to normal dentine
        
        Because mineral HAP composition increases
  - - - Deposited at specific sites in response to severe external stimuli
        
        E.g. caries, attrition, cavity prep
        
        Microleakage dissolution of dentine matrix protein fossilised in dentine triggers cellular activity for dentine repair
      - Normally found below dead tracts
      - Less regular form of dentine
      - May have tubular structure of dysplatic matrix that may be atubular
        
        Depends on rate of deposition and severity of injury
        
        More severe --> More deposition --> More distored tubular pattern
        
        If dentine forms across over long period of time (e.g. chronic caries), it may not be able to achieve regular tubular structure
        
        Building too fast -- irregular and atubular
      - Two types
        
        Rectionary Dentine
        
        Formed by upregulation of existing odontoblasts at regions where tooth integrity is breached
        
        Usually formed in reponse to mild stimulus e.g. small progressing lesion
        
        There could be tubular continuity with physiological secondary dentine
        
        Dentine permeability is reduced
        
        Reparative Dentine
        
        Formed by newly differentiated odontoblasts-like cells from pulpal mesenchyme following the death of the original primary odontoblast
        
        In response to strong stimulus e.g. deep caries of pulp exposure
        
        Matrix is rapidly deposited and has a dysplatic, irregular structure (usually atubular)
        
        Dentine permeability is reduced
        
        No DPP, lots of bone associated proteins (osteodentin)
        
        Newly differentiated cells responsible for tertiary dentine formation produce type I collagen and dentine sialoprotein
    - - Similar in appearance to translucent dentine
        
        Due to filing of dentinal tubules
        
        Areas of dentine that lack structure and appear transparent
      - Initiated by external stimuli e.g. slowly progressing caries, attrition, abrasion
      - Tubules are plugged with apatite whitlockite crystals to reduce permeability
    - - Dark zones running from periphery to pulp (when viewed in ground sections)
      - Formed when tertiary dentine seals pulpal end of tubules following the death of primary odontoblasts due to external stimulus
        
        Or when odontoblasts retract before peritubular dentine occludes tubule
      - Appear dark under microscope
        
        Because after ground sections are prepared and mounted, mounting medium may not be able to enter sealed off tubules and hence they will remain air filled
- - - - Pale amber coloured teeth
      - Poorly adherent and easily lost teeth
      - EDJ not scalloped
      - Less irregular tubules
      - Reduced pulp and root canal space
  - - - Pulp and root canals obliterated
      - Short, blunted roots
      - Mobile teeth
      - Waterfall appearance of dentine from premature odontoblast death and dentin deposition