Sem 1

Question 1

Describe development of ectomesenchyme

Answer 1

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

Question 2

Describe formation of teeth minus root formation

Answer 2

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

Question 3

Describe root formation

Answer 3

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

Question 4

What are the clinical considerations for bud stage

Answer 4

Hypoactivity: anodontia (all teeth absent), hypodontia

Hyperactivity: supernumerary teeth, natal teeth, post permanent dentition

Question 5

Clinical considerations in cap stage

Answer 5

Defect in crown shape

• den evaginatus
• cusp of carabelli
• dens invaginates

Question 6

Clinical considerations for bell stage

Answer 6

Amelogenesis imperfecta (defective histodifferentiation of ameloblasts),enamel hypoplasia (abnormal synthesis and secretion of organic matrix)

Question 7

Compare surface enamel and subsurface enamel

Answer 7

Surface enamel is harder, denser, less porous and less soluble. Has more fluoride and less carbonate and magnesium

Question 8

The 3 types of water in enamel

Answer 8

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

Question 9

Describe enamel basic structure

Answer 9

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

Question 10

Describe cross striations

Answer 10

Daily increments of growth laid down by ameloblasts. Perpendicular to long axis of enamel rods. 4-6um apart. Diurnal rhythmicity

Question 11

Lines of retizius

Answer 11

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

Question 12

Describe hunter schreger bands

Answer 12

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

Question 13

Describe enamel spindles

Answer 13

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

Question 14

Describe enamel tufts

Answer 14

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

Question 15

Describe enamel lamellae

Answer 15

Linear enamel defects throughout entire thickness of enamel. Hypomineralised. Due to incomplete maturation of group of enamel prisms.

Question 16

What happens to enamel when it gets older

Answer 16

Reduced permeability. Cannot regenerate.

Question 17

What is special about dentine as a mineralised tissue

Answer 17

Only mineralised tissue that is innervated. Mostly unmyelinated, small number of exons pass between odontoblastic cell bodies to enter dentinal tubules

Question 18

Properties of dentine

Answer 18

• 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

Question 19

What are the functions of dentinal fluid

Answer 19

• 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

Question 20

Chemical composition of dentine

Answer 20

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

Question 21

Compare mineralisation of mantle dentine and circumpulpal dentine

Answer 21

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

Question 22

Why are dentinal tubules narrower at EDJ than at pulp

Answer 22

Dentine closer to pulp developed more recently. Peritubular dentine deposited over time along the walls of dentine tubules, narrowing the tubule.

Question 23

Compare intertubular and peritubular dentine

Answer 23

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

Question 24

Describe hyaline layer of hopewell smith

Answer 24

• 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

Question 25

Describe interglobuar dentine

Answer 25

- beneath mantle layer in crown beneath granular layer in root - separate circumpulpal and mantle dentine - due to incomplete fusion of calcospherites, uncalcified

Question 26

How does EDJ prevent delamination (4)

Answer 26

- 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

Question 27

How is line of Owen formed

Answer 27

Coincidence of secondary curvatures on sigmoidal dentine tubule at border of primary and secondary dentine

Question 28

Describe incremental lines in dentine

Answer 28

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

Question 29

How are neonatal lines formed

Answer 29

Between prenatal and post natal dentine. Abrupt change in environment changes matrix compositional variation. Primary teeth and first permanent molars

Question 30

What is translucent dentine

Answer 30

Due to physiological aging, dentine tubules completely occluded by peritubular dentine, resulting in translucency. Higher concentration of mineral hydroxyapatite, more prone to fracture

Question 31

Compare primary, secondary , tertiary dentine

Answer 31

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

Question 32

What are dead tracts

Answer 32

Dark zones from periphery to pulp, seen in ground section of tooth. Tertiary dentine seals pulpal end of tubule following death of original odontoblasts

Question 33

How does sclerotic dentine reduce permeability

Answer 33

Fill dentinal tubule. Tubules plugged with whitlockite crystals

Question 34

What are the factors that help bacterial penetration of pulp (4)

Answer 34

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

Question 35

Dentinogenesis imperfecta

Answer 35

Glycine substitution in collagen 1 or mutation of dental sialophosphoprotein gene. No scalloped EDJ, enamel easily lost, reduced number of tubules, reduced pulp

Question 36

Dentine dysplasia

Answer 36

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

Question 37

Layers of pulp

Answer 37

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

Question 38

Describe junctions in pulp

Answer 38

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

Question 39

Composition of pulp

Answer 39

Loose connective tissue, 75% water 25% organic material

Question 40

What are the cells present in the pulp

Answer 40

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

Question 41

Why is ecm of pulp special

Answer 41

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

Question 42

Describe blood circulation in pulp

Answer 42

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

Question 43

Lymphatic drainage of pulp

Answer 43

Discontinuous basement membrane Remove high molecular weight solute from interstitial fluid Transport antigens directly to lymph nodes

Question 44

Innervation of pulp

Answer 44

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

Question 45

Function of pulp

Answer 45

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

Question 46

What happens to pulp as it ages

Answer 46

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)