Tooth Development

Question 1

What does the periodontium consist of?

Answer 1

• Cementum
• Periodontal ligament
• Alveolar bone
• Gingiva

Question 2

Cementum - Overview? Thickness? Adherence? Properties? Cycle?

Answer 2

• Thin layer of calcified tissue covering radicular dentine
• 10-15um in thickness (cervically)
• 50-200um thickness (apically)
• Can exceed 600um at root apex
• Adheres to dentine and the periodontal ligament
• Capable of repair and regen
• Formed throughout life, allowing reattach of PDL
• Always a layer of uncalcified precementum

Question 3

Cementum - Physical properties?

Answer 3

Physical properties:

• pale yellow
• dull surface
• softer than dentine
• permeable (more than dentine)
• easily abraded cervically

Question 4

Cementum - Chemical composition?

Answer 4

65% inorganic, 23% organic and 12% water (by weight)
Inorganic:
- hydroxyapatite, with other calcium forms (thin plate like apatite crystals)
Organic:
- Col I, and non-collagen elements (sialoprotein and osteopontin)

Question 5

Classification of Cementum - Different types?

Answer 5

• Cellular and Acellular
• Extrinsic and Intrinsic fibres
• Combination of both
• Afibrillar cementum

Question 6

Classification of Cementum - Acellular vs Cellular?

Answer 6

Acellular: no cells
- variation in arrangement
- primary cementum
- covers dentine
- appears structureless 
Cellular: cells
- contains cementocytes
- mainly in apical area and inter-radicular areas overlying acellular cementum
- secondary cementum
- lacunae present
- widely spaced incremental lines (variable growth times)
- precementum
- cementocytes (inactive) trapped in lacunae with canaliculi (oriented towards the PDL, as source of energy)
- lines of Salter (incremental lines)
Afibrillar:
- histologically look like a dark line and between hyaline and acellular cementum

Question 7

Cementum - Origin of organic matrix? Extrinsic vs Intrinsic fibres?

Answer 7

Extrinsic fibres:
- derived from Sharpey's fibres of PDL
- sharpey's fibres enter the cementum perpendicular to root surface
Intrinsic fibres:
- derived from cementoblasts
- run parallel to root surface

Mixture of all types of cementum

Question 8

Cementum - Acellular extrinsic fibre cementum? Overview? Location? Thickness?

Answer 8

• Mainly over cervical 2/3 of root
• Bulk cementum in premolars
• First formed cementum
• Reach 15um in thickness
• All Col fibres extrinsic
• Ground substance may be product of cementoblasts

Question 9

Cementum - Cellular intrinsic fibre cementum? Insertion? Location? Speed?

Answer 9

• Intrinsic fibres parallel to the root surface
• No role in PDL attachment
• Apical third of root and interradicular area
• Formed slowly

Question 10

Mixed fibre cementum - Overview? Orientation? Bundle sizes? Acellular vs Cellular?

Answer 10

Overview:
- both extrinsic and intrinsic fibres
Orientation:
- almost at right angles
Bundle sizes:
- extrinsic fibres ovoid or round (5-6um d)
- intrinsic fibres are 1-2um in diameter
Acell vs Cell:
- Acell forms slowly but well mineralised
- Cell forms quickly but less mineralised (esp at core)

Question 11

Afibrillar cementum - Overview? Distribution? Mineralisation? Origin? Location?

Answer 11

Overview:

• no collagen fibers
• sparsely distributed
• well mineralised ground substance
• epith in origin (hyaline)
• thin, acell could overlap enamel
• found between fibrillar cementum and dentine

Question 12

Cemento-Dentinal Junction - Overview? Role? Composition?

Answer 12

• Intermediate layer between 2 tissues
• Anchors periodontal fibres into dentine
• Innermost cementum layer, superficial layer of root dentine, intermediate cementum and hyaline
• Wide irregular spaces that may interconnect with tubules

Question 13

Cementum - Attachment to the periodontal ligament?

Answer 13

• Fibres in the PDL run into the organic matrix of the precementum
• Mineralisation of precementum leads to incorporation of these extrinsic fibres (Sharpey’s fibres)

Question 14

Cementum - Resorption and repair?

Answer 14

• Roots show small localised areas of resorption
• May be associated with trauma and pressure applied onto roots
• Multinuc odontoclasts
• Resorption may reach dentine
• Deficiencies resulting from resorption can be filled by deposit of cementum (reversal lines)
• Repaired cementum resembles cellular cementum (less mineralised, smaller crystals)
• Precementum like layer wide than normal precementum

Question 15

Clinical consideration - Root fractures? Cementicles?

Answer 15

Root fractures:
- repaired by cementum callus
(resorption and repair answer)
Cementicles:
- attached or free
- apical and middle thirds
- furcation areas

Question 16

Early tooth development - Initiation? Process? Basic?

Answer 16

Initiation:

• locations of teeth are established by the appearance of tooth germs
• tooth germs appear along the dental lamina (invagination in the oral mucosa)

Question 17

Early tooth development - Morphogenesis? Process? Basic?

Answer 17

Morphogenesis:

• shape of the teeth determined
• cell proliferation and movement determine shape

Question 18

Early tooth development - Histogenesis? Process? Basic?

Answer 18

Histogenesis:

• differentiation of cells takes place to produce full formed dental tissues
• histo begins during morpho as all phases overlap

Question 19

Early tooth development - Overview?

Answer 19

Early tooth development:

• primitive oral cavity, mesenchymal condensation underneath the dental epithelium takes place
• ectomesenchymal in origin (from neural tube)

Question 20

Early tooth development - 6 weeks in utero - processes?

Answer 20

• Thickening of the oral epithelium
• Invagination of the epith into the mesenchyme to form the primary epith band
• maxillary and mandibular processes with a developing tongue

Question 21

Early tooth development - 7 weeks in utero? Division? Lamina?

Answer 21

Primary epith bands divides into 2:
- vestibular lamina (buccally)
- dental lamina (lingually)
Vestibular lamina:
- contributes to the development of the vestibule
- vestibules delineate the lips and cheeks from the tooth bearing regions
- degeneration of the central epith cells producing a sulcus
Dental lamina:
- contributes to teeth formation

Question 22

Early tooth development - 8 weeks in utero?

Answer 22

• Swellings (tooth bud) develop on the deep surface of the dental lamina
• Each swelling is surrounded by mesenchymal condensation

Question 23

Early tooth development - Tooth germ formation? Stages?

Answer 23

• Tooth germs are classified into stages (bud, cap, early and late bell stage)
• Odontogenesis is a continuous procedure

Question 24

Tooth germ formation - Bud stage?

Answer 24

Bud stage:

• enamel organ appears as a simple ovid epith mass
• surrounded by mesenchyme
• mesenchyme separated from the epith by a base mem

Question 25

Tooth germ formation - Cap stage? 11 weeks in utero? Process?

Answer 25

Cap stage: - morphogenesis progresses - invagination of the deeper surface of enamel organ - peripheral cells start to be arranged as external and internal enamel epith - central cells more rounded - dental papilla and dental follicle also present

Question 26

Tooth germ formation - Cap stage? 12 weeks in utero? Formation?

Answer 26

Cap stage: - central cells in the enamel organ become separated (stellate reticulum) - (cuboidal) external enamel epith cells (form) - (columnar) internal enamel epith cells (form) - prolif of surrounding mesenchyme - dental papilla/follicle

Question 27

Tooth germ formation - Early bell stage? 14 weeks in utero? Progression? Dental follicle composition?

Answer 27

Early bell stage: - shape of the internal enamel epith decides the crown shape - mitotic activity at different sites affects the folding - contribution of available spaces and mechanical forces - dental lamina breaks (epith rests of serrez) Dental follicle: - inner vascular fibrocellular condensation - loose connective tissue layer - outer vascular layer lining the alveolus (presence of permanent tooth bud, at the same time as the primary dentition)

Question 28

Tooth germ formation - Early bell stage? 14 weeks in utero? Layers?

Answer 28

Early bell stage: 4 distinct layers; - external enamel epith - stellate reticulum - stratum intermedium - internal enamel epith

Question 29

Tooth germ formation - external enamel epithelium? Forms the? Separation? Organelles?

Answer 29

External enamel epith: - forms the outer layer of cells in enamel organ - base mem separates cells from mesenchyme (follicle) - desmosomes and gap junction

Question 30

Tooth germ formation - Cervical loop? Overview?

Answer 30

Overview: - is at the growing margin of enamel organ - lies at the junction between inner and outer enamel epith

Question 31

Tooth germ formation - Stellate reticulum? Overview? | Shape? Organelles? Role?

Answer 31

Overview: - intercellular spaces become fluid filled - star shaped branching - prominent nuc, little endoplasmic and few mito - developed golgi and microvilli (secretion) - glycosaminoglycans - synth collagen Role: - stellate reticulum protects the underlying tissues and maintains tooth shape - balance between hydrostatic Pa of stellate and papilla - effect crown outline

Question 32

Tooth germ formation - Stratum intermedium? Consists? Location? Role?

Answer 32

``` Overview: - consists of 2-3 layers of flat cells - lies over internal enamel epith Role: - protein synthesis - helps transport of material to and from internal enamel epith - concentrates materials ```

Question 33

Tooth germ formation - Internal enamel epith? Shape? Organelles? Separation?

Answer 33

Shape: - columnar Organelles: - rich in RNA and no alkaline phosphatase Separation: - from the dental papilla by base mem and cell free zone

Question 34

Tooth germ formation - Early bell stage? Dental papilla? Overview?

Answer 34

Overview: - future pulp - packed mesenchymal cells - few fibrils - rich in GAGs

Question 35

Tooth germ formation - Late bell stage? Progression of external enamel epith? Progression of dental lamina? Structure? Enamel form? Ameloblast - odontoblast relationship?

Answer 35

- Lingual downfrowths of external enamel epith gives rise to permanent anterior teeth buds (5 months) - Dental lamina grows posteriorly to give rise to the tooth buds of permanent posterior teeth (4 months) - Apposition stage (form dental hard tissue) - Hard tissues form at cusp tips - Internal enamel epith differentiate into pre-ameloblasts - Pre-ameloblasts induce adjacent mesenchymal cells to differentiate into odontoblasts - Odontoblasts produce pre-dentine and dentine - Presence of dentine induces ameloblasts to from enamel

Question 36

Transitory structures - Enamel knot? What is it? Role?

Answer 36

What is it? - localised mass of cells in centre of internal enamel epith - bulges into papilla - non-proliferative - signalling centre

Question 37

Transitory structures - Enamel cord? What is it? Role? Septum? Navel?

Answer 37

What is it: - strand of cells extending from the stratum intermedium unto the stellate reticulum Septum: - cord that completely splits the stellate reticulum Navel: - invagination where the cord meets the external enamel epith

Question 38

Epith-mesenchymal interactions - enamel organ and papilla process? signalling?

Answer 38

- the enamel organ and papilla need to induce morpho/histo differentiation - messages pass between the epith and mesenchyme

Question 39

Inductive messages - Different methods?

Answer 39

- chemical substances (hormones) - direct cell contact - ECM between 2 layers

Question 40

Clinical considerations - types of abnormalities?

Answer 40

- Congenital - Induction problems - Fusion of tooth germs - Malformations - Macro/microdontia - Peg laterals - Double tooth - Concrescence - Odontomes (invaginated, evaginated, simple and complex) - Oligo/Ano/Hyperdontia (supernumerary and supplemental) - Amelo/dentinogenesis imperfecta - Hypomineralised teeth

Question 41

Amelogenesis - Presecretory stage? 2 main components? Differentiation? Ameloblast cell cycle? Organelles? Location?

Answer 41

``` 2 main components: - differentiation of pre-ameloblasts - resorption of base mem Differentiation: - internal enamel epith cells begin to differentiate into pre-ameloblasts at cusp tip (progresses cervically) Ameloblasts: - become columnar - polarised cells (nuc at end of cell) in contact with stellate reticulum Organelles: - large nuc - small golgi (close to stratum) - RER, mito, vesicles and ribosomes near base mem - pinocytotic invag of cell mem - with gap junctions Location: - in contact with mesenchyme, but base mem still present ```

Question 42

Presecretory stage - 1st layer? enzymal secretions?

Answer 42

Presecretory stage: - first layer of predentine formed, base mem separating papilla from pre-ameloblasts disappear - enzymes released by pre-amelo degrade base mem (exocy) - resorption of degraded products (endocy)

Question 43

Presecretory stage - organelles of the cell? cell shape? End stage?

Answer 43

``` Organelles: - mito separates the nuc and cell mem - ER, golgi and vesicles enlarge (on other side) - preamelo joined by desmosomes forming proximal web Shape: - secretory end becomes irregular End stage: - cytodifferentiation is complete - synth and secrete small prots - phago by odontoblasts ```

Question 44

Secretory stage - Organelles? Prot synth? Transportation and Secretion?

Answer 44

Organelles: - prox nuc - RER oriented parallel to long axis - prom golgi Prot synth: - enamel matrix prots assembled at RER - transitional vesicles to golgi (for glycosylation and sulphation) - packed into electron dense secretory granules - transported along microtubule to secretory end (by merocrine)

Question 45

Secretory stage - Shape change and why? Process name? Prismatic orientation?

Answer 45

Secretory stage: - ameloblast form thin layer of enamel matrix and retreat - after first layer, the secretory end becomes pyramidal - Tomes' process - Different orientation of prisms due to Tomes' process forming the Hunter-Schraeger bands

Question 46

Secretory stage - Alignment and separation? Mechanical union? Tomes' process role? Vesicular conc? Hydroxyapatite?

Answer 46

- Alignment of desmosomes and tight junctions - Zonular junctions separate, forming matrix from the interior enamel organ Mechanical union: - provided by junctions at stratum end - gap junctions at diff levels to synchronise activity Tomes' process: - shape determines structure of enamel - spikes develop between adjacent processes - deposit peripheries of prisms (pits) - processes then fill prisms' cores - different orientation give rod and inter-rod of the prisms Vesicular conc: - more vesicles present - discharged at secretory end and between adjacent cells Hydroxyapatite: - appear before matrix is 50nm thick

Question 47

Secretory stage - Crystal features?

Answer 47

Crystal features: - early crystals thin - much smaller than mature - aligned perpendicular to distal surface of Tomes' process - each prism formed by 1 amelo but interprismatic formed by 4 amelo - rapid crystal growth - Tomes' process source of ions - crystals grow in direction of their conc gradient - first layer of enamel matrix is deposited while cell is flat and so no change in crystal orientation (aprismatic)

Question 48

Secretory stage overview?

Answer 48

- Secretory phase is over once the whole thickness of the enamel is formed - Tomes' processes retract and another aprismatic layer is formed

Question 49

Transition stage - Overview? Maturation? What stops?

Answer 49

Overview: - marks the transformation of secretory ameloblasts into mature form Maturation - maturation occurs via mineralisation What stops: - matrix deposition ceases and organic matrix is removed (amelogenins)

Question 50

Transition stage - Changes to ameloblasts? Ameloblast role? Developing enamel matrix composition?

Answer 50

Ameloblast changes: - height is reduced - conc reduced by 50% (apoptosis by autophagocytosis) - reduced number of protein synth organelles - invag of enamel organ with BVs Role: - form a base mem over immature enamel and attach themselves to it by hemidesmosomes Developing enamel matrix: - 90-95% is amelogenin - they are hydrophobic and aggregate - remaining 10% are enamelin and tuftelin - amelogenin are removed during enamel maturation

Question 51

Maturation stage - Overview? Process of maturation?

Answer 51

Overview: - once the entire thickness of enamel is formed, all the morpho feature are present - only 30% mineralised - maturation changes enamel into final form - crystal increase in thickness, but reduction in inter-crystalline space Process: - removal of water and amelogenins, with calcium addition with Pi to increase crystal size

Question 52

Maturation stage - Amelogenins - Characteristics?

Answer 52

Characterisitcs: - thixotropic, this readily squeezed to surface (fluid-like, time dependent change in viscosity) - thixotropic material are stable at rest but fluid when agitated Changes: - tomes' processes disappear - organelle content reduced - organelles congregate to distal end

Question 53

Maturation stage - Ameloblast changes? Degradation? Amelogenin/water removal? Ruffled phase? Smooth phase? Why alternation?

Answer 53

Ameloblast changes: - plasma mem infolds to form striated border (ruffled) - alternated with smooth ended types - alteration takes place 5-7 times (remove amelogenins) Degradation: - of enamel matrix via serine proteases prod by enamel organ - space left occupied by water (enamel becomes porous) (preceed mineral gain) - water and protein will be actively removed and mechanically squeezed out by the growing crystal Ruffled phase: - tight junctions link adj ameloblasts rendering them impermeable - influx of mineral ions into enamel - increased act of Ca ATPase Smooth phase: - tight junctions lost - allows water and amelogenin passage from enamel between ameloblasts Alternation: - movement of Ca ions (active ruffled and passive smooth) - pH changes (neutral favours mineralisation ruffled and acidic stops mineral smooth)

Question 54

Maturation stage overview?

Answer 54

- Ameloblasts produce proteinases to reduce enamel prot molecular weight (also degrad end products) - last 1/3 of maturation occurs after prot matrix removed

Question 55

Post-maturation stage - Ameloblast cycle? Separation? Enamel organ? Reduced enamel epith? Eruption?

Answer 55

``` Ameloblast: - becomes flat Separation: - primary cuticle (amorphous layer of proteins) separate enamel from cells Basal lamina reappears Enamel organ: - cells fade into the dental follicle Reduced enamel epith: - protects the tooth during eruption Eruption: - fluoride content increases in surface enamel ```

Question 56

Mineralisation - Ion source? Transport? Crystals? Amelogenins? Crystal growth?

Answer 56

Ion source: - Ca from the enamel organ Transport: - travels extracellularly (also intracell) - active transport via carriers on the cell mem - passive diffusion from plasma Control transport: - prox cell junctions between ameloblasts control passage of ions Crystals: - growth and nucleation are thought to be guided by tuftelin - initial nucleation in dentine and mineralisation crosses enamel-dentine junction Amelogenins: - involved in mineral start - assemble into nanospheres - with crystals forming between spheres - crystals grow by fusion of nuc sites - form of prismatic structure, crystals start growing in length Crystal growth: - controlled breakdown to provide space for crystals - mod inhib molecules that inhib crystal form - removed prots are deposit around ameloblasts and control thickness of deposited enamel

Question 57

Enamel defects - Types?

Answer 57

- Localised trauma - Fluorosis - Erythroblastosis fetalis Amelogenesis imperfecta: - hypoplastic/calcified/maturation

Question 58

Dentinogenesis - epithelial-mesenchymal interactions? Changes? Protein composition? GFs?

Answer 58

- Epithelial is the enamel organ - Mesenchymal is the ectomesechyme from the neural crest (papilla) - induction signal from the ectodermal epith - changes in composition of basement membrane of internal enamel epith - laminin, chondroitin and enamel prots - fibronectin and decorin (distal end future odonto) - GF expressed in internal enamel epith - TGFb trapped and released from base mem

Question 59

Dentinogenesis - cytodifferentiation of odontoblasts? Origin? Cell divisions? initiation? Organelles? Overview?

Answer 59

- differnritate from ectomesenchymal cells, after signal from the preameloblasts is secreted - predetermined number of cell divisions before differentiation - differentiation starts at the cusp tip or incisal edge - enlargement if preodontoblasts, nuclei away from enamel organ, golig complex and rough endoplasmic reticulum, rearrange cytoskeleton - fibronectin bind protein on cell membrane - cell processes directed towards the enamel organ - 1 large process with dominate, increased fuel-cell junctions - synchrony through gap junctions (dentine formation needs to be uniform)

Question 60

Dentinogenesis - deposition of dentin matrix? Abundant component? Structure? Special part?

Answer 60

Abundant structure: - Col I Structure: - collagen is secreted into extracellular matrix as tropocollagen which consists of 3 alpha polypeps chains to from a helical structure - the helical structure leaves hole zones between the matrix, allowing future liberalisation

Question 61

Dentinogenesis - deposition of dentine matrix? Collagen? Location? Strength?

Answer 61

- Col I (fibrillar collagen) Location: - secretary into ECM as tropocollagen (polymerises to collagen) which consists of 3 alpha polypetide chains, forming a helical structure (these holes left enable other substances to associate to the collagen) - tropoclooagen aligned in a quatre stagger arrangement (cross-link) Strength: - crosslinking, but with age tissues become stiffer and loses elasticity

Question 62

Dentinogenesis - deposition of dentine matrix? Process? Other components? DPP?

Answer 62

Process: - initial collagen fibres lie at right angles to dentino-enamel junction - Col I deposited from cell body (moves inward) - Col fibres in circumpulpal dentine parallel with dentino-enamel junction - Andresen lines (changes in orientation, incremental lines) Other components: - dentine phosphoprotein (2nd most abundant) - DPP role in mineralisation and epith-mesench sig - both prots secreted by pre/odontoblasts (DPP from odontoblastic process DPP: - at hole zones

Question 63

Dentinogenesis - deposition of dentine matrix? Factors controlling matric formation?

Answer 63

Factors: - initial effect of signals from dental epith - systemic disturbances - pulp cells effect and injury - efferent nerves

Question 64

Dentinogenesis - dentine mineralisation (mantle) - process?

Answer 64

Process: - cell budding form matric vesicles - matrix vesicles carry alkaline phosphatase leading to concentrations of Pi ions in vesicles and develop crystals

Question 65

Dentinogenesis - dentine mineralisation (circumpulpal) - process? DPP influence? Crystal location?

Answer 65

Process: under control of DPP (bind Ca) - odontoblasts control the transport and release of Ca - Ca conc in organelles distally - presence and distribution of matrix components can initiate and modulate mineralisation - Ca transported by odontoblasts becomes a crystalline mineral deposited onto template by Col I DPP: - changes in conform allow it to bind more Ca leading to form and grow crystals - at high conc inhibit crystal form - this, odontoblasts control mineralisation by controlling DPP conc Crystal location: - appear in hole zones

Question 66

Dentinogenesis - Dentinophosphoprotein role in mineralisation? Other substances in mineralisation?

Answer 66

- Transport of ions to the mineralisation front - location of nucleation nonspecific regions in the collagen fibrils - stabilisation of crystals Other substances: - osteonectin - osteopontin - bone sialoprotein - chondroitin sulphate 4/6

Question 67

Dentinogenesis - circumpulpal - mineralisation types? Calcospheres?

Answer 67

- always a zone of mineralisation (appears irregular) - linear, spherical or both mineralisation - calcospheres fuse (if not complete interglobular dentine will form) - calcospheres appear around matrix vesicles in mantle and initial mineralisation sites in circumpulpal

Question 68

Dentinogenesis - formation of intratubular dentine - characteristics? Matrix content? Produced by? Physiological process? Factors for formation?

Answer 68

Small crystals in amorphous matrix Matrix content: - glycoprot, proteogly, lipids, osteonectin, osteocalcin and bone sialoprotein Produced by: - odontoblasts and diffused plasma proteins Physiological process: - small tubules (lateral processes) - main process surrounded by intratubular dentine Factors for formation: - aging

Question 69

Dentinogenesis - formation of secondary dentine - stimulus? Changes?

Answer 69

``` Stimulus: - age Changes: - apoptosis of odontoblasts (pulp volume decreases) - 50% reduction after 4 years - leads to tubule direction change ```

Question 70

Dentinogenesis - formation of teritary dentine? Stimuli? Types? Characterisitics? Signalling molecules?

Answer 70

Stimuli: - low grade to the pulp Types: - atubular, tubular and irregular - newly differentiated Signalling molecules: - TGFb and BMP released from pre/dentine by plaque acids - TGFb time morentubular dentine - BMP stimson more bone like dentine formation - atubular dentine more common under aggressive lesions

Question 71

Dentinogenesis - Inherited defects in dentine - types?

Answer 71

Dentinogenesis imperfecta - Type I/II | Dentine dysplasia - Tyoe I/II

Question 72

Root development - root formation? Initial step? Epithelial shelves?

Answer 72

``` Initial step: - when enamel and dentine formation are well advanced, the external and internal enamel epith at the cervical loop form a double layered root sheath - this is called Hertwig's root sheath Hertwig root sheath: - no stellate reticulum - proliferated apically - outlines shape of root Epithelial shelves: - grow to demarcated the location of multiple roots ```

Question 73

Root developmental - follicle forms? odonto induced by? separation sheath? cementoblast diff?

Answer 73

Process: - dental follicle forms cementum, periodontal ligament and alveolar bone - differentiation of odontoblasts induced by inner layer of sheath - dentine formation followed by separation of the sheath cells (rests of Malassez) - differentiation of cementoblasts from mesenchymal cells in follicle

Question 74

Root development - root dentine formation - characterisitcs? Comparison to crown dentine?

Answer 74

- hyaline layer first - initial collagen fibres are parallel to the cemento-dentine junction - the odontoblastic processes branch and loop - formation of the granular layer of Tomes (dark layer) - epith remnants in peripheral dentine (slower than coronal) - smaller initial calcospheres and more interglobilar dentine

Question 75

Cementogenesis - acellular cementum? Process location? Process continuation? Characterisitcs? Non-collagenous proteins?

Answer 75

Process location: - starts at the cervical margin and extends apically Continuation: - hertwigs root sheath - differentiation of odontoblasts - disintegration of root sheath - fibroblast-like cells in the follicle become cemebtoblasts - cemebtiblasts secrete collagen fibrils - form a strong union with dentinal collagen Characterisitcs: - fibrous fringe at surface - cells may retreat with adjacent periodontal ligament fibroblasts - mineralisation of first layer of rootndentone is by matrix vesicles - delayed mineralisation of the outermost layer of the hyaline layer, and this mineralisation spreads to the fibres severed by fibroblasts like cementoblasts - making the first few microns of cementum firmly attached to dentine Non-collagenous proteins: - produced by cementoblasts - involved in chemoattraction, cell attachment, cell differentiation, mineralisation and bonding to dentine

Question 76

Cementogenesis - acellular cementum - continuous maintenance? Difference to other types of cementum?

Answer 76

Continuous maintenance: - slow increase in thickness (2-2.5um) - secretion of ground substance by polarised cementoblasts - continuity between periodontal fibres and fibrous fringe - before continuity is established, mainly acellular intrinsic fibre cementum - slow mineralisation of collagen Differences: - do not control mineralisation of matrix - matrix vesicles not observed - presense of hydroxyalatite crystal in dentine initiates mineralisation in cementum - periodontal fibroblasts are alkaline phosphatase rich - no calcospheres - formed so slowly that no evidence of precementum layer - show incremental line (closer together)

Question 77

Cementogenesis - acellular afibrillar cementum - location?

Answer 77

Location: - thin overlying enamel - reduced enamel epith is lost or damaged - cells in follicle come in contact with enamel and differentiate ino cementoblasts - produce an afibrillar matrix that calcifies (enamel matrix induce differentiation)

Question 78

Cementogenesis - cellular cementum - location? Characterisitics? Cementoblasts? Difference to acellular?

Answer 78

Location: - mainly in apical root third, and furcation area Characterisitics: - form around eruption time - faster tissue formation - following disintegration of root sheaths large basophilic cells differentiate in follicle (distinct layer of cementoblasts) - mainly intrinsic fibres - no role in tooth attachment - alternating layers of intrinsic and extrinsic acell cementum - variations in combinations and thickness Cementoblasts: - secrete collagen (intrinsic fibres) and ground substance - finres parallel tonroot surface - thin precementum layer with linear mineralisation - multiple secretion leads to cell entrapment - cementoblasts trapped in lacunae become cementocytes - new cementoblasts form stem cells in PDL Difference to acellular: - more cytoplasm and more processes - widely spread incremental lines (saltor)

Question 79

Enamel Pearl - what is it?

Answer 79

What is it: - small droplet of enamel on the root near the furcation - budding of Hertwig's root sheath