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histology > Dentin > Flashcards

Dentin Flashcards

1
Q

where is dentin located

A
  • in crown and root of tooth
  • make up bulk of tooth
  • encloses and is intimately associated with tooth pulp
  • not visible clinically in an intact tooth, unless attrition or abrasion removing enamel or cementum
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2
Q

what is the ectodermal origin

A
  • from dental papilla - mesenchyme
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3
Q

is dentin living tissue

A
  • odontoblasts and intercellular substance

- dentin production continues life of tooth

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4
Q

what is the elasticity like in dentin

A
  • can flex better than enamel
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5
Q

what is the hardness of dentin like

A
  • harder than bone; softer, less calcified than enamel

- less mineralized salts (hydroxyapatite crystals), more radiolucent in rad

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6
Q

what is the colour of dentin

A
  • yellow in colour – clinical colour of tooth
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7
Q

what is the chemical composition of dentin

A
  • 70% inorganic hydroxyapatite

- 30% organic and water - ground substance and collagen fibres and protein

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8
Q

what are 3 distinct microscopic areas of dentin

A
  1. dentinal tubule
  2. peritubular dentin
  3. intertubular dentin
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9
Q

what are dentinal tubules

A
  • long tube running from DEJ to dentinocemento junction (walls of root) to the pulp
  • may be branched at the DEJ end; tubules contain odontoblast process - from the odontoblast in the pulp
  • straight - bottom 1/2 root and cusp area
  • s-shaped - sides of tooth (smooth surfaces) and top 1/2 root
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10
Q

what is peritubular dentin

A
  • hardest
  • higher mineral content surrounding the dentinal tubules (outer portion of dentin tubules)
  • peritubular dentin more calcified around tubule than intertubule
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11
Q

what is intertubular dentin

A
  • 2nd hardest

- makes up bulk of dentinal material (between tubes holding them together)

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12
Q

how does dentin develop

A
  • odontoblastic process (goes through the tubule)
  • cytoplasmic extensions of the cell body
  • remainder cytoplasm stretched out like thin nail into dentinal tubule
  • plays role in pain sensation
  • nerve terminals close to odontoblastic cell body and dentin tubules in prevention
  • young teeth extend to DEJ - could be why children feel cavities faster and more intensely than adults
  • older teeth - shorter
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13
Q

when and how does dentin begin developing

A
  • starts at 5th embryonic development week
  • begins from the DEJ or DCJ -> pulp
  • begins release of ground substance -> odontoblasts
  • cell walls (cytoplasm) remain attached to DEJ/DEC (unlike ameloblasts)
  • minerals (HA) are also deposited into ground substance -> act cement
  • minerals crystallize and harden dentin
  • but dentin remain perforated by millions of holes - dentinal tubules
  • odontoblast cell body (with nucleus) remains in pulp
  • only odontoblastic process remains in mineralized tissue
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14
Q

what is the appearance of dentinal tubules

A
  • straight lines -> cusp area, bottom 1/2 of root

- s-shaped curves -> smooth surfaces, top 1/2

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15
Q

what are the 3 types of dentin

A
  • primary dentin
  • secondary dentin
  • tertiary dentin (two types: reparative dentin and sclerotic dentin)
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16
Q

what is primary dentin

A
  • everything we discussed so far
  • dentin is formed before eruption and some is still forming after eruption
  • primary dentin is formed in a tooth before the completion of the apical foramen or until teeth occlude
  • dentin does continue to form and repair throughout life
17
Q

what is secondary dentin

A
  • normal physiological process due to occlusion biting and chewing forces
  • begins forming when newly erupted tooth contacts another tooth
  • basically - occlusal forces cause secondary dentin to form in order to protect the pulp
  • slow apposition of dentin throughout like (only during pulp vitality)
  • results in decrease of pulp size (deposit towards pulp)
  • compared to primary dentin: formed more slowly than primary dentin, less mineralized, tubules present a slight shift in path
18
Q

what is tertiary dentin

A
  • two types
    1. reparative dentin (reactive)
  • formed quickly in response to caries, filling tooth, attrition, occlusal trauma, and recession
  • also NOT deposited evenly along pulpal wall, more irregular course than secondary dentin
  • appears as localized deposits to side injury towards pulp
    2. sclerotic dentin
  • mostly present in older teeth, increases with age (odontoblastic process dies and withdraws from tubules)
  • usually located beneath areas of attrition or slow progressing caries
  • also located in areas of recessions where cementum is exposed -> under tomes granular layer (band of unmineralized spots beneath cementum … granular appearance)
  • deposit of calcium salts in form of peritubular dentin
  • results decrease tubular size blocking access to pulp
  • clinical significance: slows caries progression, decreases/eliminated sensitivity
19
Q

what is predentin

A
  • dentinoid
  • layer dentin adjacent to pulp
  • organic matrix of dentin not yet fully mineralized
  • present in young teeth during dentin formation (primary dentin)
  • area of production of future dentin (secondary dentin)
  • indicates the incremental (layer upon layer) or pattern by which dentin is formed called von Ebner lines
20
Q

what is interglobular dentin

A
  • refers to uncalcified or hypocalcified areas of dentin
  • small areas near DEJ or DCJ
  • near tomes granular layer
  • caused by metabolic disturbances during tooth development
21
Q

what is the tomes granular layer

A
  • refers to uncalcified spots along root
  • underneath cementum overlying end dentinal tubules (DT)
  • very sensitive area
  • allows more penetration of hot/cold and touch odontoblastic process (OP)
22
Q

what are dead tracts

A
  • refers to area beneath trauma (usually caries)
  • bacteria enter DT
  • odontoblastic process degenerates and DT fills with air
  • can provide fast and easy pathway for bacteria and acid because they are empty and open at both ends
  • odontoblast attempt to block tubules by forming reparative dentin
  • dead tracks can also become sclerotic - blocked to prevent passage of bacteria/decay
23
Q

what is the clinical importance of dentin

A
  • influences progression of caries
  • influences pattern and speed
  • decay progresses towards dentin
  • reaches tubules
  • bacterial enters tubules smaller sizes than tubules
  • destroy odontoblast
  • path DT leads day apically towards pulp
  • horizontal spread of caries more rapid in dentin vs enamel
  • defence reactions to decay:
  • production of reparative dentin (tertiary dentin): increases thickness dentin, slows progression
  • production of sclerotic dentin: calcium salts deposited in DT from pulp, blocks tubules from bacterial invasion
24
Q

what causes tooth sensitivity

A
  • gradual recession of gingiva, exposing cementum and removed cementum exposing dentinal tubules
  • most common cause of sensitivity
  • common to have sensitivity in areas where tubules are open
  • absence of sensitivity in areas where tubules are closed
25
Q

how is sensitivity affected with time

A
  • sensitivity can decrease with time
  • the longer exposed cementum and dentin exists, the less sensitive it becomes
  • odontoblatic process degenerates
  • saliva constituants - calcium salts and phosphorus assist in blocking tubules
26
Q

when is sensitivity usually experienced

A
  • when breathing cold air
  • eating hot/cold foods
  • brushing incorrectly
  • if patient follows proper hygiene instructions sensitivity can be eliminated or reduced

histology (15 decks)

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