Sem 1 Flashcards
Describe development of ectomesenchyme
Gastrulation. Bilayered embryonic disc. Epiblast invaginate into hypoblast layer to form endoderm. Epiblast differentiate to form ectoderm. Second wave of invagination form mesoderm. Ectoderm differentiate to form neural plat, primitive streak, fold and pinch off, neural tube and neural crest cells. Neural crest cells migrate into mesoderm —> ectomesenchyme
Describe formation of teeth minus root formation
Oral epithelial cells above ecto mesenchyme proliferate faster than surrounding cells, horse shoe shape, form primary epithelial band, give rise to vestibule lamina and dental lamina. Buds on dental lamina given rise to by dental placode signal. Correspond to deciduous dentition. Lingual extension correspond to permanent dentition. Cap stage, invagination of dental lamina on deep surface of enamel organ. Dental follicle made of cuboidal cells that will form PDL and cementum. Dental papilla made of columnar cells that will form dentine and pulp. Stellate reticulum cells in enamel organ are star shaped connected by desmosomes. Bell stage. IEE differentiate to form pre ameloblasts, stimulate outer dental papilla cells to differentiate to odontoblasts, stimulate pre ameloblasts to form ameloblasts. Signal odontoblasts to lay down predentine, cells move into enamel organ to lay down new layers of matrix as ameloblasts stimulated to lay down enamel matrix. Dental lamina distegrate
Describe root formation
HERS formed by fusion of IEE and OEE at cervical loop. HERS grows horizontally into dental papilla to form epithelial root sheath. Stimulate dental papilla cells to differentiate into odontoblasts and lay down radicular dentine. HERS secretes hyaline layer of hopewell smith. Elongation of HERS after tooth eruption due to proliferation. Follicle cells adhere to hyaline layer, differentiate to cementoblasts + to periodontal fibroblasts that lay down collagen fibres to form PDL
What are the clinical considerations for bud stage
Hypoactivity: anodontia (all teeth absent), hypodontia
Hyperactivity: supernumerary teeth, natal teeth, post permanent dentition
Clinical considerations in cap stage
Defect in crown shape
- den evaginatus
- cusp of carabelli
- dens invaginates
Clinical considerations for bell stage
Amelogenesis imperfecta (defective histodifferentiation of ameloblasts),enamel hypoplasia (abnormal synthesis and secretion of organic matrix)
Compare surface enamel and subsurface enamel
Surface enamel is harder, denser, less porous and less soluble. Has more fluoride and less carbonate and magnesium
The 3 types of water in enamel
Extra crystalline water: mobile, bulk of enamel
Caged/zeoltic water: caged in apatite crystals, not tightly bound
Intracellular water: associated with lattice or hydroxy group in unit cells
Describe enamel basic structure
Basic unit is enamel prism, composed mainly of calcium hydroxyapatite crystals. RUn perpendicular to EDJ to outer surface of enamel. Interprismatic space are principal diffusion pathways, fast diffusion. Intraprismatic space, diffusion pathway between hydroxyapatite crystals for diffusion. Outermost layer is aprismatic due to absence of Tome’s process; more mineralised, less porous, stronger and denser
Describe cross striations
Daily increments of growth laid down by ameloblasts. Perpendicular to long axis of enamel rods. 4-6um apart. Diurnal rhythmicity
Lines of retizius
Dark bands marking out different groups of enamel prisms formed by different cohort of ameloblasts each week. At cervical region, enamel formed more slowly, incremental lines closer together. Transversely, circumferentially, rings
Describe hunter schreger bands
Alternating dark and light bands in inner 2/3 of enamel. Change in direction of adjacent groups of enamel rods, reflect light different. Cut longitudinally, dark, cut in cross section, light
Describe enamel spindles
Odontoblastic processes that extend into ameloblasts layers during amelogenesis. Shorter than tufts. Not aligned with prisms. Protrusion of tubules of mantle dentine into enamel. Help prevent delamination
Describe enamel tufts
Small branching defects that extend into 1/3 of enamel. Stress shielding. Hypomineralised, greater concentration of enamel protein. Arise due to abrupt changes in direction of rods raiding from different regions of scalloped EDJ
Describe enamel lamellae
Linear enamel defects throughout entire thickness of enamel. Hypomineralised. Due to incomplete maturation of group of enamel prisms.
What happens to enamel when it gets older
Reduced permeability. Cannot regenerate.
What is special about dentine as a mineralised tissue
Only mineralised tissue that is innervated. Mostly unmyelinated, small number of exons pass between odontoblastic cell bodies to enter dentinal tubules
Properties of dentine
- pale yellow
- softer than enamel
- anisotropic: stress withstanding directionally dependent. Tubules perpendicular to stress more stress bearing than those parallel. Contributed by mineralised network of collagen fibrils
- hard but elastic: greater compressive tensile strength, more flexible than enamel to prevent crack propagation (less brittle)
- permeable: tubular hydrated
- dentinal fluid: transfer and dissipate occlusal force
What are the functions of dentinal fluid
- absorb shock, transfer and dissipate occlusal force/rapid movement transmit shear forces to nerves
- protective, outward flow of fluid to move bacteria out
- calcification of peritubular dentine
- flow outwards continuing immunoglobulins and antibodies
Chemical composition of dentine
Mainly hydroxyapatite crystals which give compressive strength/hardness
Organic matrix
- type 1 collagen: elasticity, scaffold fro mineralisation, parallel to pulpal surface (follow direction of EDJ), transverse to dentinal tubules (EXCEPT mantle dentine, collagen fibre perpendicular to EDJ)
- non collagenous proteins: phosphoprotein, sialoprotein, growth factors which regulate tooth development and dentinogenesis and direct tertiary dentine
Compare mineralisation of mantle dentine and circumpulpal dentine
Mantle dentine undergo globular mineralisation and vesicle mineralisation. Matrix vesicles bud off osteoblasts. Alkaline phosphatase from osteoblasts release phosphate ions inside. Form crystals. Crystals break through vesicle membrane, form calcospherites which grow and fuse to form mineralisation front.
Circumpulpal dentine undergoes linear mineralisation, crystal deposition on previously formed crystals. No globular mineral protrusions of mineralising front. More uniform rate of formation of mineralisation
Why are dentinal tubules narrower at EDJ than at pulp
Dentine closer to pulp developed more recently. Peritubular dentine deposited over time along the walls of dentine tubules, narrowing the tubule.
Compare intertubular and peritubular dentine
Peritubular dentine is laid down along walls of dentine tubule, form a ring inside the tubule. Intertubular dentine found between tubules.
Peritubular dentine 40% more mineralised, harder than intertubular dentine. (Harder, increase mechanical properties and durability of dentine)
Intertubular dentine contains collagen that provides elasticity to prevent fracture. Peritubular dentine no collagen matrix
Intertubular dentine formed via mineralisation of predentine while peritubular dentine formed via deposition of apatite crystals
Describe hyaline layer of hopewell smith
- outermost layer of root dentine
- no peritubular dentine
- no odontoblastic processes left behind, atubular
- bond cementum to dentine
- distribute occlusal stresses so that they do not concentrate in PDL
- dental follicular cells bind hyaline layer to differentiate into fibroblasts and cementoblasts
Describe interglobuar dentine
- beneath mantle layer in crown beneath granular layer in root
- separate circumpulpal and mantle dentine
- due to incomplete fusion of calcospherites, uncalcified
How does EDJ prevent delamination (4)
- scalloped pattern with th concavity towards enamel. More pronounced scalloping in areas that have to withstand higher masticatory shearing forces
- gradual change in properties
- discontinuous stress concentration
- enamel spindles interlock enamel and dentine structures
How is line of Owen formed
Coincidence of secondary curvatures on sigmoidal dentine tubule at border of primary and secondary dentine
Describe incremental lines in dentine
Circadian fluctuations in acid base balance, collagen fibril formation different.
Lines of von ebner: alternate dark and light bands 4um apart, daily activity of odontoblasts, perpendicular to dentinal tubules
Andresen lines: perpendicular to dentinal tubules, weekly rhythmicity, 6-10 pairs of short period marking in between 20-30um apart
How are neonatal lines formed
Between prenatal and post natal dentine. Abrupt change in environment changes matrix compositional variation.
Primary teeth and first permanent molars
What is translucent dentine
Due to physiological aging, dentine tubules completely occluded by peritubular dentine, resulting in translucency. Higher concentration of mineral hydroxyapatite, more prone to fracture
Compare primary, secondary , tertiary dentine
Primary dentine: before root completion
4um/day
Secondary dentine: after root completion, formed in continuity with primary dentine
Formed by downregulated odontoblasts, 0.4um a day, incremental marking closer together
Less regular tubular pattern
Deposition on pulp chamber roof and floor
Tertiary dentine: in response to external stimuli. Reactionary dentine in response to mild to moderate stimulus by unregulated odontoblasts. Less regular, more distorted tubular pattern if rate of deposition higher. Reparative dentine in response to severe stimulus. By newly differentiated (from pulpal progenitor cells) odontoblast like cells, contain high levels of bone associated proteins eg osteodentin, no dentinphosphoprotein. Death of original odontoblast
What are dead tracts
Dark zones from periphery to pulp, seen in ground section of tooth. Tertiary dentine seals pulpal end of tubule following death of original odontoblasts
How does sclerotic dentine reduce permeability
Fill dentinal tubule. Tubules plugged with whitlockite crystals
What are the factors that help bacterial penetration of pulp (4)
Deeper cavity, closer to pulp, where dentine is more porous hence easier to reach pulp
No outward flow of dentinal fluid that will flush bacteria away from pulp
Tubules must be patent ie not occluded physiologically (PTD or exogenous material eg sclerotic dentine) so that bacteria can access pulp
Must be able to pass through odpntoblastic layer
Dentinogenesis imperfecta
Glycine substitution in collagen 1 or mutation of dental sialophosphoprotein gene. No scalloped EDJ, enamel easily lost, reduced number of tubules, reduced pulp
Dentine dysplasia
Atypical dentine, abnormal pulp morphology
Type 1: short blunted roots no root canals in primary teeth. Crescent roots in adult teeth, teeth mobile. Premature cycle of odontoblast death and dentin deposition
Type 2: pulp chamber of deciduous teeth obliterated. Permanent teeth have pulp chamber that is very large in coronal portion
Layers of pulp
Odontoblastic layer adjacent to predentine
Pseudostratified, columnar (coronal) and cuboidal (root)
Long process extending into dentine and predentine
Cell free zone
Cell rich zone: undifferentiated progenitor cells
Subondontoblastic plexus
Plexus of raschkow
- sensory and autonomic nerves enter through apical foramen and branch extensively, nerve fibres terminate between odontoblasts
Plexus of blood vessels
Pulp core: predominantly fibroblasts
Describe junctions in pulp
Gap junction: communication of electrical impulses/small molecules and small molecules/ions directly between adjacent cells
Tight junction: limit permeability, maintain integrity of odontoblast layer
Intermediate junction: belt to maintain cell to cell positioning
Composition of pulp
Loose connective tissue, 75% water 25% organic material
What are the cells present in the pulp
Odontoblasts
Fibroblasts
- pulp core
- collagen fibres, slow turnover rate vs in PDL
- stellate
Immunocompetent cells
- dendritic cells, macrophages
- dentine border and pulp core
- APC
Undifferentiated progenitor mesenchymal cells
- fibroblasts and odontoblasts
Why is ecm of pulp special
Contains type 3 as well as type 1 collagen.
Type 1 collagen synthesised by odontoblasts and fibroblasts, provide consistency and strength
Type 3 collagen synthesised by fibroblasts, provide elasticity
Fibronectin, bind to membrane receptor protein, mediate cell-cell adhesion
Describe blood circulation in pulp
Microcirculatory system. Absorb low molecular weight solute. Arteriovenous shunt becomes active during inflammation for regional control of pulpal blood flow. Reduce inflammation due to low compliance of dentine
Lymphatic drainage of pulp
Discontinuous basement membrane
Remove high molecular weight solute from interstitial fluid
Transport antigens directly to lymph nodes
Innervation of pulp
Sympathetic efferent fibre of trigeminal nerve modulate blood flow (motor)
Myelinated A fibre at pulp dentine border for sharp piercing pain, sensitivity to hot and cold
Unmyelinated C fibre in core, throughout pulp, dull pain, toothache
Function of pulp
Inductive: dental papilla cells interact with inner enamel epithelium of enamel organ to affect crown shape
Formative: initiate tooth formation, differentiation into ameloblasts and odontoblasts
Protective: nerve endings mediate sense of pain
Defensive: dentinal fluid contain immunoglobulins + outward flow of fluid to wash bacteria away from pulp, intratubular fibres to trap bacteria, inflammatory response mounted by immunoglobulin cells + compartmentalism day to area of pulp with dentine breach + tertiary dentine
Sensory: odontoblasts function as mechanical and thermo receptor
What happens to pulp as it ages
Pulp volume decreases due to deposition of secondary dentine
Fewer cells
Fewer blood vessels and nerves due to decreased inherently healing ability
Increased thickness and number of collagen fibres
More pulpal calcifications (pulp stones)
