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CSP4 YR5 - Paeds RESET > Tooth Development > Flashcards

Tooth Development Flashcards

1
Q

What does the periodontium consist of?

A
  • Cementum
  • Periodontal ligament
  • Alveolar bone
  • Gingiva
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2
Q

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

A
  • 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
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3
Q

Cementum - Physical properties?

A

Physical properties:

  • pale yellow
  • dull surface
  • softer than dentine
  • permeable (more than dentine)
  • easily abraded cervically
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4
Q

Cementum - Chemical composition?

A

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)

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5
Q

Classification of Cementum - Different types?

A
  • Cellular and Acellular
  • Extrinsic and Intrinsic fibres
  • Combination of both
  • Afibrillar cementum
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6
Q

Classification of Cementum - Acellular vs Cellular?

A 
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
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7
Q

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

A 
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

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8
Q

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

A
  • 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
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9
Q

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

A
  • Intrinsic fibres parallel to the root surface
  • No role in PDL attachment
  • Apical third of root and interradicular area
  • Formed slowly
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10
Q

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

A

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)

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11
Q

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

A

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
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12
Q

Cemento-Dentinal Junction - Overview? Role? Composition?

A
  • 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
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13
Q

Cementum - Attachment to the periodontal ligament?

A
  • 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)
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14
Q

Cementum - Resorption and repair?

A
  • 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
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15
Q

Clinical consideration - Root fractures? Cementicles?

A 
Root fractures:
- repaired by cementum callus
(resorption and repair answer)
Cementicles:
- attached or free
- apical and middle thirds
- furcation areas
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16
Q

Early tooth development - Initiation? Process? Basic?

A

Initiation:

  • locations of teeth are established by the appearance of tooth germs
  • tooth germs appear along the dental lamina (invagination in the oral mucosa)
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17
Q

Early tooth development - Morphogenesis? Process? Basic?

A

Morphogenesis:

  • shape of the teeth determined
  • cell proliferation and movement determine shape
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18
Q

Early tooth development - Histogenesis? Process? Basic?

A

Histogenesis:

  • differentiation of cells takes place to produce full formed dental tissues
  • histo begins during morpho as all phases overlap
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19
Q

Early tooth development - Overview?

A

Early tooth development:

  • primitive oral cavity, mesenchymal condensation underneath the dental epithelium takes place
  • ectomesenchymal in origin (from neural tube)
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20
Q

Early tooth development - 6 weeks in utero - processes?

A
  • 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
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21
Q

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

A

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

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22
Q

Early tooth development - 8 weeks in utero?

A
  • Swellings (tooth bud) develop on the deep surface of the dental lamina
  • Each swelling is surrounded by mesenchymal condensation
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23
Q

Early tooth development - Tooth germ formation? Stages?

A
  • Tooth germs are classified into stages (bud, cap, early and late bell stage)
  • Odontogenesis is a continuous procedure
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24
Q

Tooth germ formation - Bud stage?

A

Bud stage:

  • enamel organ appears as a simple ovid epith mass
  • surrounded by mesenchyme
  • mesenchyme separated from the epith by a base mem
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25
Q

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

A

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
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26
Q

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

A

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
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27
Q

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

A

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)

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28
Q

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

A

Early bell stage: 4 distinct layers;

  • external enamel epith
  • stellate reticulum
  • stratum intermedium
  • internal enamel epith
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29
Q

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

A

External enamel epith:

  • forms the outer layer of cells in enamel organ
  • base mem separates cells from mesenchyme (follicle)
  • desmosomes and gap junction
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30
Q

Tooth germ formation - Cervical loop? Overview?

A

Overview:

  • is at the growing margin of enamel organ
  • lies at the junction between inner and outer enamel epith
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31
Q

Tooth germ formation - Stellate reticulum? Overview?

Shape? Organelles? Role?

A

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

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32
Q

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

A 
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
33
Q

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

A

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

34
Q

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

A

Overview:

  • future pulp
  • packed mesenchymal cells
  • few fibrils
  • rich in GAGs
35
Q

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

A
  • 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
36
Q

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

A

What is it?

  • localised mass of cells in centre of internal enamel epith
  • bulges into papilla
  • non-proliferative
  • signalling centre
37
Q

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

A

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

38
Q

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

A
  • the enamel organ and papilla need to induce morpho/histo differentiation
  • messages pass between the epith and mesenchyme
39
Q

Inductive messages - Different methods?

A
  • chemical substances (hormones)
  • direct cell contact
  • ECM between 2 layers
40
Q

Clinical considerations - types of abnormalities?

A
  • 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
41
Q

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

A 
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
42
Q

Presecretory stage - 1st layer? enzymal secretions?

A

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)
43
Q

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

A 
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
44
Q

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

A

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)

45
Q

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

A

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
46
Q

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

A
  • 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
47
Q

Secretory stage - Crystal features?

A

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)
48
Q

Secretory stage overview?

A
  • Secretory phase is over once the whole thickness of the enamel is formed
  • Tomes’ processes retract and another aprismatic layer is formed
49
Q

Transition stage - Overview? Maturation? What stops?

A

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)

50
Q

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

A

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

51
Q

Maturation stage - Overview? Process of maturation?

A

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

52
Q

Maturation stage - Amelogenins - Characteristics?

A

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

53
Q

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

A

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)

54
Q

Maturation stage overview?

A
  • Ameloblasts produce proteinases to reduce enamel prot molecular weight (also degrad end products)
  • last 1/3 of maturation occurs after prot matrix removed
55
Q

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

A 
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
56
Q

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

A

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

57
Q

Enamel defects - Types?

A
  • Localised trauma
  • Fluorosis
  • Erythroblastosis fetalis
    Amelogenesis imperfecta:
  • hypoplastic/calcified/maturation
58
Q

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

A
  • 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
59
Q

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

A
  • 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)
60
Q

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

A

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

61
Q

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

A
  • 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
62
Q

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

A

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

63
Q

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

A

Factors:

  • initial effect of signals from dental epith
  • systemic disturbances
  • pulp cells effect and injury
  • efferent nerves
64
Q

Dentinogenesis - dentine mineralisation (mantle) - process?

A

Process:

  • cell budding form matric vesicles
  • matrix vesicles carry alkaline phosphatase leading to concentrations of Pi ions in vesicles and develop crystals
65
Q

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

A

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

66
Q

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

A
  • 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
67
Q

Dentinogenesis - circumpulpal - mineralisation types? Calcospheres?

A
  • 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
68
Q

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

A

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

69
Q

Dentinogenesis - formation of secondary dentine - stimulus? Changes?

A 
Stimulus:
- age
Changes:
- apoptosis of odontoblasts (pulp volume decreases)
- 50% reduction after 4 years
- leads to tubule direction change
70
Q

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

A

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

71
Q

Dentinogenesis - Inherited defects in dentine - types?

A

Dentinogenesis imperfecta - Type I/II

Dentine dysplasia - Tyoe I/II

72
Q

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

A 
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
73
Q

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

A

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
74
Q

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

A
  • 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
75
Q

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

A

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

76
Q

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

A

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)

77
Q

Cementogenesis - acellular afibrillar cementum - location?

A

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)
78
Q

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

A

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)

79
Q

Enamel Pearl - what is it?

A

What is it:

  • small droplet of enamel on the root near the furcation
  • budding of Hertwig’s root sheath

CSP4 YR5 - Paeds RESET (7 decks)

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