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Craniofacial and Tooth Biology > 20. Tooth Root Development and Cementum > Flashcards

20. Tooth Root Development and Cementum Flashcards

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1
Q

Tooth root formation is coordinated with …

A

development of periodontium

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2
Q

Explain reciprocal tissue interactions in cervical loop during tooth crown formation

A
  • inner enamel epithelium of cervical loop is separated from dental papilla cells by cell-free zone
  • IEE cells become elongated (preameloblasts) and secrete signalling molecules to induce odontoblast differentiation from dental papilla cells
  • odontoblasts align and produce predentin
  • signals from odontoblasts in predentine induce differentiation of preameloblasts into ameloblasts that start producing preenamel
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3
Q

How do reciprocal interactions during tooth crown formation compare to tooth root formation?

A
  • very similar
  • just no ameloblasts in roots
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4
Q

Stages of root formation

A
  • formation of Hertwig’s epithelial root sheath (HERS)
  • induction of odontoblasts and root dentine formation
  • root completion
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5
Q

Explain formation of Hertwig’s epithelial root sheath (first stage of root formation)

A
  • once crown formation complete
  • epithelial cells of IEE and OEE initially proliferate downwards from cervical loop of enamel organ to form double layer of epithelial cells, HERS
  • HERS extends around and closes the pulp and defines shape of future root
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6
Q

Difference in cervical loop in root formation

A
  • no stratum intermediate and no stellate reticulum
  • similar reciprocal interactions between HERS and dental papilla are thought to occur
  • but genetic factors are not well studied
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7
Q

Proteins in epithelium

A
  • PTHrP
  • enamel proteins (transient)
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8
Q

Proteins in mesenchymal

A
  • TGF-beta
  • BMP
  • RUNX2
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9
Q

What do proteins in mesenchyme cause?

A
  • cementoblast differentiation
  • periodontal regeneration
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10
Q

Explain ‘induction of odontoblasts and root dentine formation’ (second stage of root formation)

A
  • IEE of HERS induces odontoblast differentiation
  • no ameloblast differentiation occurring like crown
  • odontoblasts secrete predentine that mineralises to form root dentine
  • curved end of HERS is termed epithelial diaphragm and outlines primary apical foramen
  • growth of dentine layer causes HERS to be stretched and epithelial cells degenerate in this area
  • continued growth of HERS, odontoblast induction and dentine formation until root is finished
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11
Q

At eruption stage, tooth root is only … of final length
What does this mean?

A
  • 65%
  • wide, open root apex
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12
Q

Explain root completion (3rd stage of root formation)

A
  • 1.5 years in primary teeth
  • 3 years in permanent teeth
  • very narrow apical foramen formed - blood vessels and nerves run
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13
Q

How are multiple rooted teeth formed?

A
  • HERS encloses pulp and appears as a curtain hanging down
  • primary apical formation divides by fusion of epithelial folds (ingrowths) from HERS (formed in avascular areas)
  • secondary apical foramina
  • formation of three rooted tooth
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14
Q

Explain root elongation after root formation

A
  • HERS produces new epithelial cell proliferation
  • but it doesn’t grow downwards into underlying connective tissue
  • HERS position remains stationary
  • consequently when root dentine is formed the tooth root is growing/moving upwards
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15
Q

Role of root elongation in tooth eruption

A
  • growth replacement theory (disproved)
  • rootless teeth can erupt
  • periodontal ligament promotes eruption via rearrangement of collagen fibres and contraction
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16
Q

Layers of root dentine

A
  • cementum
  • hyaline layer
  • Tome’s granular layer
  • root dentine
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17
Q

Cementum is a/cellular, has fibrils/doesn’t and is solid/granular

A
  • acellular
  • doesn’t
  • granular
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18
Q

Hyaline layer of root dentine is analogous to …

A

mantle dentine of crown

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19
Q

Features of hyaline layer in root dentine

A
  • non-tubular
  • structureless layer of dentine
  • 20 micrometres
  • first dentine formed
  • possibly bonds dentine to cementum
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20
Q

2 explanations of Tome’s granular layer

A
  • extensive branching and backward looping of odontoblast processes
  • incomplete fusion of calcospherites (like interglobular dentine)
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21
Q

Root dentine is considered similar to coronal dentine but …

A
  • collagen fibres deposited parallel and at a distance from basal lamina of HERS
  • root dentine less mineralised and mineralises faster
  • less phosphophoryn (dentine phosphoprotein - binds calcium and regulates dentine mineralisation)
22
Q

Role of phosphoryn

A
  • dentine phosphoprotein
  • binds calcium and regulates dentine mineralisation
23
Q

Define ‘cementum’

A
  • avascular connective tissue covering roots
24
Q

Cementum is produced by …

A

cementum-forming cells (cementoblasts)

25
Q

Function of cementum

A
  • attachment of root dentine to periodontal ligament
  • to alveolar bone via Sharpey’s collagen fibres
26
Q

Composition of cementum by weight

A
  • 40 to 50% hydroxyapatite (similar to bone but harder and more mineralised)
  • type 1 (90%), 3 and 7 collagens
  • alkaline phosphatase, bone sialoprotein, dentine matrix protein 1, osteoclacin, osteonectin, osteopontin
  • similar proteins to dentine and bone
27
Q

Classifications of cementum

A
  • on absence or presence of cells is acellular (primary) or cellular (secondary)
  • on origin of collagen fibres in cementum - extrinsic or intrinsic
28
Q

Stages of cementogenesis

A
  • odontoblast induction and dentine formation
  • stretching and disintegration of HERS
  • differentiation of dental follicle cells into osteoblasts, fibroblasts and cementoblasts
29
Q

2 theories of cementoblast differentiation

A
  • undifferentiated dental follicle cells can migrate through gaps in disintergrating HERS and receive iinductive signals from newly formed predentine and/or HERS cells
    OR
  • HERS cells undergo epithelial-mesenchymal transition (EMT) to become cementoblasts (or a partial contribution)
30
Q

How does early formation of cementum occur?

A
  • cementoblasts align along newly formed hyaline dentine (predentine)
  • extension of cell processes into predentine and deposition of collagen fibrils that intermingle with unmineralised predentine matrix (collagen fibres)
  • extension of collagen fibres and stitching of PDL fibres to fibrous fringe
  • mineralisation of predentine spreads through cementum and traps fibres
  • strong connection of cementum to dentine
  • further embedding of fibres into cementum through PDL
31
Q

Differences between acellular and cellular cementum

A
  • no cells vs lacunae and canaliculi (directed towards PDL) containing cementocytes and processes
  • border with dentine not clearly demarcated vs clearly demarcated
  • rate of development slow vs fast
  • incremental lines close together vs wider
  • precementum layer virtually absent vs present
32
Q

Incremental growth lines in cementum are called …

A

Lines of Salter

33
Q

Cementum enamel junction differs in people. Percentages?

A
  • 60% cementum overlaps enamel
  • 30% cementum meets enamel
  • 10% they don’t meet
34
Q

Distribution of acellular cementum

A
  • covers root adjacent to dentine
  • primary attachment
35
Q

Distribution of cellular cementum

A
  • found in apical and interradicular areas
  • adaptation and repair
  • thickness of cellular cementum increases with age
36
Q

Role of acellular vs cellular cementum

A
  • primary attachment
  • adaptation and repair
37
Q

Give 2 developmental anomalies in cementum

A
  • free cementicle (completely split off)
  • sessile cementicle (protrusion from cementum)
38
Q

Cementicles are usually … and caused by …

A

– acellular
- unknown, protentially microtrauma

39
Q

What are cementicles?
What happens to them?

A
  • detachment of a group of cementoblasts
  • free cementicles may become incorporated as sessile or embedded cementicles as thickness of cementum layer increases
40
Q

What are epithelial rests of Malessez?

A
  • HERS become stretched and degenerates by apoptosis
  • leaves behind a group of epithelial cells in periodontal ligament (near root surface)
  • involved in periodontal repair?
  • source of epithelial stem cells?
41
Q

Explain enamel pearls

A
  • epithelial rests can form enamel pearls (mostly on root surface in bifurcation areas of maxillary molars)
  • can cause plaque accumulation and periodontal disease
42
Q

Explain enamel pearl formation

A
  • localised attachment of epithelilal cell rests to predentine (caused by absence of cementum deposition)
  • molecular signs from predentine could initiate ameloblast differentiation
  • when HERS/root development is initiated, stratum intermedium/stellate reticulum cells of cervical loop can be trapped in subset of epithelial cell rests
  • combine both these theories is the idea
43
Q

Define ‘concrescence’

A
  • union of two teeth after eruption
  • resulting from fusion of cementum surfaces
44
Q

Causes and clinical considerations regarding consrescence

A
  • trauma and tooth crowding
  • radiograph and surgery .
45
Q

Define ‘dilacerated roots’

A

curved or bent roots

46
Q

Causes and clinical considerations of dilacerated roots

A
  • developmental trauma (for example playground incidents in children)
  • radiograph and careful extraction
47
Q

Cause and clinical consideration of multiple roots/root canals

A
  • abnormal folding of HERS
  • radiograph and variation of extraction technique
  • careful cleaning of extra root canal during endodontic treatment
48
Q

What needs to be remembered about the complex root canal system?

A
  • endodontic treatment can be difficult
  • failure to notice and clean accessory root canals is a common cause of persistant infection after root canal treatment
49
Q

Mechanism of lateral root canal formation

A
  • continuity of HERS is interrupted too early
  • during root dentin formation e.g a blood capillary running between dental papilla and dental follicle
  • this interface affects local formation of odontoblasts resulting in canal in dentine connecting dental pulp and PDL of mature tooth
  • frequently found at root apex
50
Q

Define ‘hypercementosis’

A
  • abnormally increased production of cementum
51
Q

Causes of hypercementosis

A
  • age change
  • idiopathic
  • Paget’s disease
  • occlusal trauma (bruxism)
52
Q

Clinical considerations of hypercementosis

A
  • difficult to extract
  • increased distance from CE junction to root apex for endodontic treatment

Craniofacial and Tooth Biology (25 decks)

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