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Oral Histology > L11 > Flashcards

L11 Flashcards

1
Q

The periodontium: “Around the tooth” - The support system for the tooth

A

Cementum
Alveolar bone
Periodontal ligament (PDL)
Gingiva: Tooth-associated and gingival ligaments

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2
Q

Hertwig’s epithelial root sheath (HERS)

what is it?

A

Extension of enamel organ, transforms from cervical loop

Bilayer structure of IEE and OEE

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3
Q

Hertwig’s ERS

What does it do?

A

“Architect” of the root defining size and shape (morphogenesis)
Induces root odontoblast differentiation

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4
Q

But how do you get multiple roots?

A

Epithelial growth – epithelial interradicular process(es) = tongues of epithelium growing toward one another

Apical foramina (plural

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5
Q

Hertwig’s epithelial root sheath (HERS):

A

Differentiation of the root
Differentiation of root odontoblasts
Epithelial-mesenchymal signaling

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6
Q

Dental papilla:

A

Undifferentiated ectomesenchymal cells

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7
Q

HERS induces dental papilla cells to

A

differentiate to pre-odontoblasts, then odontoblasts

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8
Q

Root dentin forms in step with

A

HERS proliferation

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9
Q

HERS is a

A

transient structure

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10
Q

HERS disintegrates shortly after

A

inducing root odontoblast differentiation

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11
Q

Some HERS cells become

A

epithelial rests of Malassez (ERM)

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12
Q

Epithelial rests of Malassez (ERM)

A

ERM appear as clumps, strands, or networks of cells in the PDL
Surrounded by basement membrane
Sometimes close to root, sometimes several cell layers away
Function(s)? Can cause cysts. Also speculated to be involved with periodontal homeostasis or regeneration, but not proven…

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13
Q

Root dentin

continuous with

A

crown dentin

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14
Q

Dentinogenesis largely the same as crown

A

(exception: Interacting with IEE of HERS instead of IEE of enamel organ)

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15
Q

Cells:

A

Ectomesenchyme&raquo_space; Dental papilla&raquo_space; Pre-odontoblasts&raquo_space; Odontoblasts
Types: Mantle dentin, circumpulpal dentin, predentin, primary/secondary/tertiary dentin, etc.

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16
Q

Epithelial-mesenchymal signaling in root

HERS

A 
Smad4 transcription factor (TF)
Sonic hedgehog (SHH) secreted signal → papilla cells
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17
Q

Dental papilla

A

Induces Gli1 TF
Downstream Nfic TF
Odontoblast differentiation

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18
Q

Without Nfic, dental papilla cannot respond to

A

HERS signaling and cells do not differentiate into odontoblasts
Result: Rootless teeth!

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19
Q

Developmental root defects

A

Defects of HERS growth and/or root dentin formation
Can make teeth prone to breakage, exfoliation, ankylosis, or cause difficult extraction and other issues

Dilaceration: deformity in shape/direction
“Rootless teeth”
Taurodontism: large pulp chamber at expense of root/furcation

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20
Q

Cementum comes in two main types

Defined by:

A

Presence/absence of cells within its matrix
Origin of collagen fibers of the matrix

Major types you need to be familiar with:
Acellular cementum = Acellular extrinsic fiber cementum (AEFC) = Primary cementum
Cellular cementum = Cellular intrinsic fiber cementum (CIFC) = Secondary cementum

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21
Q

Acellular cementum =

A

Acellular extrinsic fiber cementum (AEFC) = Primary cementum

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22
Q

Cellular cementum =

A

Cellular intrinsic fiber cementum (CIFC) = Secondary cementum

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23
Q

Cellular mixed stratified cementum (CMSC): A mix of =

A

alternating acellular and cellular layers

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24
Q

2 major types of cementum:

A

primary accellular cementum (covers 2/3rds of root).

Secondary Acellular cementum (covers apical 1/3rd of root)

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25
Q

Acellular afibrillar cementum

A

at CEJ

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26
Q

Acellular cementum

A

Cervical 2/3 of root
Primary cementum = formed first
Acellular extrinsic fiber cementum (AEFC)
No cells included

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27
Q

Cellular cementum

A

Apical 1/3 of root
Secondary cementum = second formed
Cellular intrinsic fiber cementum (CIFC)
Cementocytes included

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28
Q

Cementum: Attachment: Cementum important for

A

strong periodontal structure; “cementing” the tooth in the socket (acellular cementum primarily)

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29
Q

Cementum: Protecting root from

A

resorption and repairing resorption pits

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30
Q

Cementum: Adjusting

A

tooth position (Cellular cementum only)

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31
Q

Cementum: Sealing

A

dentin tubules – hydrodynamic theory of dental sensitivity, inhibiting bacterial invasion

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32
Q

Cementum composition and properties

A 
Composition (similar to bone, dentin)
~50% inorganic: Mineral (hydroxyapatite)
35% organic: Collagen type I (90%),            other non-collagenous proteins and glycosaminoglycans (10%)
15% water
Physiology (different from bone)
Avascular
Non-innervated
No turnover – growth by apposition
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33
Q

Classic hypothesis for cementum origins:

A

Ectomesenchyme > dental follicle > cementoblast

Fenestration of HERS allows follicle cells (pre-cementoblasts) to access root surface

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34
Q

Alternative hypothesis for cementum origins:

A

Dental epithelium > HERS > Epithelial-mesenchymal transformation to cementoblast

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35
Q

Cementoblasts

A

Origin: (Thought to be derived) from dental follicle (ectomesenchyme)
Function: Make acellular and cellular cementum
Products: Collagens, extracellular matrix (ECM) proteins, enzymes that promote cementum mineralization
Fate: Remain in PDL close to cementum surface, regulate slow cementum growth throughout life; direct cementum repair

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36
Q

Cementocytes

A

Origin: A subset of cementoblasts becomes embedded in cellular cementum matrix (i.e. from dental follicle, ectomesenchyme)
Function: ????????
Products: Much less than cementoblasts
Features: Reside in lacuna (small space in the matrix), extend dendrites (cell processes) through canaliculi (small tunnels) to communicate and receive nutrients
Fate:
Some remain in lacunae for life
Some deep lacunae appear empty- cementocyte death?

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37
Q

Dental follicle (dental sac)

A

Ectomesenchymal origin
Precursors to: Cementoblasts, PDL fibroblasts, osteoblasts
We don’t know exactly how specific follicle cells become specific differentiated cells, but location is part of it

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38
Q

Root dentin –

A

the “scaffold” for cementum formation

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39
Q

HERS disintegrates, exposing

A

root dentin surface

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40
Q

Cementoblast differentiation

From

A

dental follicle

Remain on/near root surface

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41
Q

Initial collagen fibers

A

Cementoblasts secrete these
Intermingle with dentin at the CDJ
These short fibers are intrinsic, not yet connected with PDL

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42
Q

Dentin-cementum junction (DCJ)

A

Cementum initial collagen fiber bundles intermingle with dentin collagen fibers
Dentin completes mineralization
DCJ remains a less hard “cushion” interface between cementum and dentin

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43
Q

PDL Fibroblasts

A

Produce primary collagen fiber bundles of PDL space

Stitched to first cementum intrinsic fibers

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44
Q

Extrinsic fibers

A

Continuity of extrinsic fibers and initial intrinsic fibers

These will become mineralized Sharpey’s fibers within cementum

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45
Q

Extrinsic fibers are the

A

MAJOR fiber group for acellular cementum

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46
Q

Extrinsic fibers enter

A

acellular cementum at HIGH DENSITY

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47
Q

Extrinsic fibers are critical to the

A

FUNCTION of acellular cementum

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48
Q

Dense, highly organized Sharpey’s fibers (in red) inserting into both the

A

acellular cementum and alveolar bone

These are mineralized collagen fiber bundles providing strong anchorage of tooth-PDL-bone

49
Q

Additional views of acellular cementum and Sharpey’s fibers

A

Note lines perpendicular to root surface– mineralized collagen (Sharpey’s) fibers

50
Q

Continuation of cementogenesis

A

Mineralization of fibers
Cementoblasts promote hydroxyapatite deposition between and within collagen fibers
Sharpey’s fibers are mineralized collagen fibers continuous with PDL, also found in alveolar bone

51
Q

Collagen substrate (type I and others) -

A

the scaffold

52
Q

Cells secrete non-collagenous extracellular matrix (ECM) proteins that participate in

A

mineral precipitation

53
Q

Cells direct mineralization in and between

A

collagen fibers, e.g. by ECM proteins and enzymes

54
Q

Progressive mineralization of

A

extrinsic collagen fibers

55
Q

Progressive mineralization of

A

extrinsic collagen fibers

56
Q

Mechanism of acellular cementum mineralization

A 
Fiber fringe (FF) before cementum initiation
FF becomes engulfed and mineralized = Sharpey’s fibers
Mineralization continues slowly over time (~3 mm/yr)
57
Q

(Secondary) Cementoblasts

Produce

A

cementum matrix rapidly – cementoid

Produce many intrinsic collagen fibers, deposit the cellular cementum ECM

58
Q

Cellular cementum: Often minimal or absent in

A

incisors and canines = little role in tooth attachment

59
Q

Cellular cementum: “Adaptive cementum” maintains

A

tooth in proper occlusal position by compensating for enamel attrition throughout life

60
Q

Cellular cementum can repair

A

cementum resorption anywhere on root

61
Q

Mechanism of cellular cementum mineralization

A

A clear unmineralized cementoid
Equivalent to predentin or osteoid
Cementoblast secretes collagen and other proteins&raquo_space; Time lag&raquo_space; Matrix mineralizes
Conditions that delay/inhibit mineralization may affect cementoid similarly to osteoid

62
Q

Cementocytes

Embedded in

A

cellular cementum matrix
Connected to one another and surface (PDL)
Equivalent to osteocytes in bone?

63
Q

Both acellular and cellular cementum continue

A

growing SLOWLY throughout life

64
Q

No remodeling/turnover– cementum

A

appositional growth (adding to the existing layer)

65
Q

Longitudinal lines/striations/appositional growth lines indicate

A

successive layers

BUT resorption does sometimes occur…

66
Q

Reparative cementum

A

Following root cementum resorption by osteoclasts/odontoclasts
Repair cementum fills resorption pit (Howship’s lacuna)
Reparative cementum is often cellular, regardless of location (i.e. even on cervical root)
Concerns:
Is new cementum well bonded with dentin (i.e. quality of CDJ)?
Is new cementum well attached to PDL (i.e. density of extrinsic fibers?)

67
Q

What can go wrong with cementum?

too little

A

Too little: cementum aplasia or hypoplasia

68
Q

What can go wrong with cementum?

too much

A

Too much: hypercementosis, possibly leading to ankylosis

69
Q

What can go wrong with cementum? Loss of cementum

A

Loss of cementum: External root resorption

70
Q

Hypophosphatasia

A

Rare skeletal disease
Mutations in ALPL, gene for tissue-nonspecific alkaline phosphatase (TNAP protein)
TNAP breaks down pyrophosphate (PPi), an inhibitor of mineralization
HPP: High PPi
Acellular cementum aplasia or hypoplasia

71
Q

HPP affects

A

bone (skeletal and craniofacial), dentin, and enamel

72
Q

Acellular cementum most dramatically

HPP

A

affected tissue in terms of severity and prevalence

73
Q

HPP

Defective/absent cementum →

A

Loose teeth, premature loss of primary and/or secondary teeth

74
Q

Hypercementosis

A

Excessive cementum growth
Trauma, genetic disease, idiopathic
Generally asymptomatic, may cause ankylosis and difficulty in extraction
Unusual example of genetic hypercementosis that is opposite of HPP

75
Q

What factors are important in mineralization?

acellular cementum

A

Bone sialoprotein (BSP)
First discovered in bone, but also present in dentin and cementum
Promotes hydroxyapatite mineral formation
Critical role in acellular cementum formation
BSP knock-out mouse has cementum hypoplasia, PDL detachment, periodontal breakdown
No known human equivalent, though phenotype consistent with some aspects of aggressive periodontitis

76
Q

Root resorption (external)

A

Odontoclasts (osteoclast-like cells)
Very common to have “mild” resorption in 1 or more teeth
Excessive orthodontic force (usually apical effect)
Related to trauma, severe periodontitis, genetic factors
“Idiopathic”

77
Q

Multiple idiopathic cervical root resorption

A

very aggressive, no treatment

78
Q

Root (surface) caries

A

Bacteria/plaque initiated
Exposed root surface
Soft, progressive lesion – distinct from clastic resorption

79
Q

Alveolar bone structure

A

Alveolar process/alveolar bone forms the socket that holds the tooth
Tooth-associated bone
Cortical plates (buccal/lingual)
Trabecular bone (spongiosa)
Alveolar plate is the focus for today’s lecture- the most involved with periodontal function
More in lecture 11 by Dr. Sun…

80
Q

Alveolar bone:

A

The partner of cementum

Includes extrinsic collagen fiber bundles, mineralized Sharpey’s fibers (similar to acellular cementum)
Primary fibers entering bundle bone are larger in diameter and less dense (vs. cementum)
Bundle bone,

81
Q

Bundle bone =

A

Bundle bone = Bone lining the socket, inner aspect facing tooth root

82
Q

Lamina dura=

A

Radiographic feature of alveolar bone
Radiopaque layer lining the socket
Increased radiopacity from thick bone without trabeculation, NOT because of increased mineral content

83
Q

Lamina dura is

A

Lamina dura is opaque (radiopaque)

84
Q

PDL is

A

radiolucent

85
Q

Cribriform plate = structure pierced by

A

many small holes

86
Q

Bone remodeling in

A

response to function – osteoclasts and osteoblasts work in tandem

87
Q

“Clasts” and their role in resorption

A

Normal remodeling of alveolar bone- FASTEST remodeling bone in the body
Normal bone resorption allowing tooth eruption
Normal tooth resorption when deciduous teeth are exfoliated
Abnormal when clasts resorb the roots of permanent teeth

88
Q

Alveolar bone – tooth interactions

Alveolar bone distributes

A

occlusal loads

89
Q

Existence of alveolar bone depends on

A

this interaction with dentition

90
Q

“Mechanostat” theory of bone loading

A

Bone loading causes growth (e.g. tennis player effect)
Bone unloading causes loss (e.g. astronaut effect)
Edentulous mandible gradually loses alveolar bone

91
Q

The periodontal ligament (PDL)

A

Soft fibrous connective tissue between tooth and alveolar bone (i.e. occupies the periodontal space)

92
Q

Ligament =

A

Fibrous connective tissue connecting bone to bone

93
Q

Periodontal ligament connects bone to tooth in a unique joint called a

A

gomphosis, or tooth socket

Normal width ~ 0.1 - 0.4 mm (BUT varies by person and tooth) is tightly regulated in health

94
Q

Functions of PDL

Supportive:

A

Primary collagen fibers attach tooth to bone

95
Q

Functions of PDL

Nutritive:

A

Blood supply to cells of the region, including cementoblasts and cementocytes

96
Q

Functions of PDL

Sensory:

A

Innervated for sensing position and pain

97
Q

Functions of PDL

Defensive:

A

Delivers immune cells including macrophages and neutrophils

98
Q

Functions of PDL

Maintenance/Reparative:

A

Contains stem and progenitor cells that can repair or regenerate PDL, bone, cementum

99
Q

Functions of PDL

Adaptive:

A

Based on mechanical loading (functional input), adapts fiber orientations and influences neighboring alveolar bone remodeling
Optimal arrangement to accept and distribute tensile forces from mastication
Even after orthodontic tooth movement, PDL returns to same width

100
Q

Composition of PDL

Ground substance”

A

Amorphous background material

Proteins, proteoglycans, water

101
Q

Composition of PDL

Collagen fibers

A

Collagen types I, III, XII major types
Fiber bundles – “spliced rope”
97% of fibers

102
Q

Composition of PDL

Oxytalan fibers

A

Small elastic fibers, support collagen fibers and blood vessel walls
3% of fibers
NO elastic fiber bundles = PDL is more stiff for withstanding forces

103
Q

PDL principal fiber groups

Collagen fiber bundles spanning PDL from mature tooth to bone (*except transseptal group is tooth-tooth)
Function:

A

Resist intrusive and extrusive forces, tipping and lateral movements
Defined by location or orientation
6 groups: TAHOAI
Oblique group is predominant- main group resisting occlusal loads (intrusive force)

104
Q

Transseptal fibers travel from

A

tooth to tooth

105
Q

Fibroblasts

A

Majority of cells in PDL
Secrete and remodel matrix
Intimately associated with collagen fibers- cells may act as mechanotransducers

106
Q

Other PDL cells

A 
Cementoblasts
Osteoblasts, Osteoclasts
Epithelial rests of Malassez (ERM)
Stem/progenitor cells: Ability to differentiate and regenerate
Immune cells
107
Q

PDL is

A

well vascularized
Superior and inferior alveolar arteries
Perforating vessels, sometimes called alveolar or intra-alveolar – MAJOR route
Apical routes and gingival vessel routes also

108
Q

Venous drainage in - PDL

A

axial direction

109
Q

Gingival crevicular fluid (GCF)

A

Found in the sulcus/gingival margin
Transudate from vasculature
Diagnostic value

110
Q

(1) Free endings, tree-like

A

Most common, found along the length of the root

Nociceptors and mechanoreceptors

111
Q

(2) Ruffini endings

A

(slowly adapting, found in skin)
Found near apex
Mechanoreceptors

112
Q

(3) Coiled endings

A

Mid-region of PDL

Function unknown

113
Q

(4) Encapsulated endings

A

Found near apex

Function unknown

114
Q

Cementicle

A

Ectopic cementum in PDL, attached or unattached

115
Q

Ankylosis

A

Cementum-bone fusion

Loss of PDL space

116
Q

Gingival epithelium

A

Oral epithelium
Sulcus epithelium
Junctional epithelium

117
Q

Junctional epithelium

A

Enamel and cementum
Barrier to microbial invasion
Fast turnover
(Recall, this is derived from leftover enamel organ/reduced enamel epithelium)

118
Q

Gingival ligament groups

A

Not PDL, but collagen fiber bundles spanning from tooth/bone to gingiva/connective tissue
In lamina propria (underlying connective tissue) of the gingiva
Function: Resist gingival displacement
4 groups: CDDA (transseptal group sometimes included, but we are grouping with PDL)

Oral Histology (14 decks)

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