Tooth Development Flashcards
1
Q
What does the periodontium consist of?
A
- Cementum
- Periodontal ligament
- Alveolar bone
- Gingiva
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
3
Q
Cementum - Physical properties?
A
Physical properties:
- pale yellow
- dull surface
- softer than dentine
- permeable (more than dentine)
- easily abraded cervically
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)
5
Q
Classification of Cementum - Different types?
A
- Cellular and Acellular
- Extrinsic and Intrinsic fibres
- Combination of both
- Afibrillar cementum
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
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
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
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
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)
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
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
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)
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
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
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)
17
Q
Early tooth development - Morphogenesis? Process? Basic?
A
Morphogenesis:
- shape of the teeth determined
- cell proliferation and movement determine shape
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
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)
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
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
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
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
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
25
Tooth germ formation - Cap stage? 11 weeks in utero? Process?
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
26
Tooth germ formation - Cap stage? 12 weeks in utero? Formation?
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
27
Tooth germ formation - Early bell stage? 14 weeks in utero? Progression? Dental follicle composition?
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)
28
Tooth germ formation - Early bell stage? 14 weeks in utero? Layers?
Early bell stage: 4 distinct layers;
- external enamel epith
- stellate reticulum
- stratum intermedium
- internal enamel epith
29
Tooth germ formation - external enamel epithelium? Forms the? Separation? Organelles?
External enamel epith:
- forms the outer layer of cells in enamel organ
- base mem separates cells from mesenchyme (follicle)
- desmosomes and gap junction
30
Tooth germ formation - Cervical loop? Overview?
Overview:
- is at the growing margin of enamel organ
- lies at the junction between inner and outer enamel epith
31
Tooth germ formation - Stellate reticulum? Overview?
| Shape? Organelles? Role?
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
32
Tooth germ formation - Stratum intermedium? Consists? Location? Role?
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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
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33
Tooth germ formation - Internal enamel epith? Shape? Organelles? Separation?
Shape:
- columnar
Organelles:
- rich in RNA and no alkaline phosphatase
Separation:
- from the dental papilla by base mem and cell free zone
34
Tooth germ formation - Early bell stage? Dental papilla? Overview?
Overview:
- future pulp
- packed mesenchymal cells
- few fibrils
- rich in GAGs
35
Tooth germ formation - Late bell stage? Progression of external enamel epith? Progression of dental lamina? Structure? Enamel form? Ameloblast - odontoblast relationship?
- 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
Transitory structures - Enamel knot? What is it? Role?
What is it?
- localised mass of cells in centre of internal enamel epith
- bulges into papilla
- non-proliferative
- signalling centre
37
Transitory structures - Enamel cord? What is it? Role? Septum? Navel?
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
Epith-mesenchymal interactions - enamel organ and papilla process? signalling?
- the enamel organ and papilla need to induce morpho/histo differentiation
- messages pass between the epith and mesenchyme
39
Inductive messages - Different methods?
- chemical substances (hormones)
- direct cell contact
- ECM between 2 layers
40
Clinical considerations - types of abnormalities?
- 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
Amelogenesis - Presecretory stage? 2 main components? Differentiation? Ameloblast cell cycle? Organelles? Location?
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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
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42
Presecretory stage - 1st layer? enzymal secretions?
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
Presecretory stage - organelles of the cell? cell shape? End stage?
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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
Secretory stage - Organelles? Prot synth? Transportation and Secretion?
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
Secretory stage - Shape change and why? Process name? Prismatic orientation?
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
Secretory stage - Alignment and separation? Mechanical union? Tomes' process role? Vesicular conc? Hydroxyapatite?
- 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
Secretory stage - Crystal features?
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
Secretory stage overview?
- Secretory phase is over once the whole thickness of the enamel is formed
- Tomes' processes retract and another aprismatic layer is formed
49
Transition stage - Overview? Maturation? What stops?
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
Transition stage - Changes to ameloblasts? Ameloblast role? Developing enamel matrix composition?
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
Maturation stage - Overview? Process of maturation?
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
Maturation stage - Amelogenins - Characteristics?
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
Maturation stage - Ameloblast changes? Degradation? Amelogenin/water removal? Ruffled phase? Smooth phase? Why alternation?
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
Maturation stage overview?
- Ameloblasts produce proteinases to reduce enamel prot molecular weight (also degrad end products)
- last 1/3 of maturation occurs after prot matrix removed
55
Post-maturation stage - Ameloblast cycle? Separation? Enamel organ? Reduced enamel epith? Eruption?
```
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
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56
Mineralisation - Ion source? Transport? Crystals? Amelogenins? Crystal growth?
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
Enamel defects - Types?
- Localised trauma
- Fluorosis
- Erythroblastosis fetalis
Amelogenesis imperfecta:
- hypoplastic/calcified/maturation
58
Dentinogenesis - epithelial-mesenchymal interactions? Changes? Protein composition? GFs?
- 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
Dentinogenesis - cytodifferentiation of odontoblasts? Origin? Cell divisions? initiation? Organelles? Overview?
- 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
Dentinogenesis - deposition of dentin matrix? Abundant component? Structure? Special part?
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
Dentinogenesis - deposition of dentine matrix? Collagen? Location? Strength?
- 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
Dentinogenesis - deposition of dentine matrix? Process? Other components? DPP?
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
Dentinogenesis - deposition of dentine matrix? Factors controlling matric formation?
Factors:
- initial effect of signals from dental epith
- systemic disturbances
- pulp cells effect and injury
- efferent nerves
64
Dentinogenesis - dentine mineralisation (mantle) - process?
Process:
- cell budding form matric vesicles
- matrix vesicles carry alkaline phosphatase leading to concentrations of Pi ions in vesicles and develop crystals
65
Dentinogenesis - dentine mineralisation (circumpulpal) - process? DPP influence? Crystal location?
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
Dentinogenesis - Dentinophosphoprotein role in mineralisation? Other substances in mineralisation?
- 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
Dentinogenesis - circumpulpal - mineralisation types? Calcospheres?
- 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
Dentinogenesis - formation of intratubular dentine - characteristics? Matrix content? Produced by? Physiological process? Factors for formation?
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
Dentinogenesis - formation of secondary dentine - stimulus? Changes?
```
Stimulus:
- age
Changes:
- apoptosis of odontoblasts (pulp volume decreases)
- 50% reduction after 4 years
- leads to tubule direction change
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70
Dentinogenesis - formation of teritary dentine? Stimuli? Types? Characterisitics? Signalling molecules?
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
Dentinogenesis - Inherited defects in dentine - types?
Dentinogenesis imperfecta - Type I/II
| Dentine dysplasia - Tyoe I/II
72
Root development - root formation? Initial step? Epithelial shelves?
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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
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73
Root developmental - follicle forms? odonto induced by? separation sheath? cementoblast diff?
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
Root development - root dentine formation - characterisitcs? Comparison to crown dentine?
- 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
Cementogenesis - acellular cementum? Process location? Process continuation? Characterisitcs? Non-collagenous proteins?
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
Cementogenesis - acellular cementum - continuous maintenance? Difference to other types of cementum?
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
Cementogenesis - acellular afibrillar cementum - location?
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
Cementogenesis - cellular cementum - location? Characterisitics? Cementoblasts? Difference to acellular?
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
Enamel Pearl - what is it?
What is it:
- small droplet of enamel on the root near the furcation
- budding of Hertwig's root sheath
