Dentin

Question 1

where is dentin located

Answer 1

• 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

Question 2

what is the ectodermal origin

Answer 2

• from dental papilla - mesenchyme

Question 3

is dentin living tissue

Answer 3

• odontoblasts and intercellular substance

- dentin production continues life of tooth

Question 4

what is the elasticity like in dentin

Answer 4

• can flex better than enamel

Question 5

what is the hardness of dentin like

Answer 5

• harder than bone; softer, less calcified than enamel

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

Question 6

what is the colour of dentin

Answer 6

• yellow in colour – clinical colour of tooth

Question 7

what is the chemical composition of dentin

Answer 7

• 70% inorganic hydroxyapatite

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

Question 8

what are 3 distinct microscopic areas of dentin

Answer 8

1. dentinal tubule
2. peritubular dentin
3. intertubular dentin

Question 9

what are dentinal tubules

Answer 9

• 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

Question 10

what is peritubular dentin

Answer 10

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

Question 11

what is intertubular dentin

Answer 11

• 2nd hardest

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

Question 12

how does dentin develop

Answer 12

• 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

Question 13

when and how does dentin begin developing

Answer 13

• 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

Question 14

what is the appearance of dentinal tubules

Answer 14

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

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

Question 15

what are the 3 types of dentin

Answer 15

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

Question 16

what is primary dentin

Answer 16

• 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

Question 17

what is secondary dentin

Answer 17

• 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

Question 18

what is tertiary dentin

Answer 18

• 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

Question 19

what is predentin

Answer 19

• 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

Question 20

what is interglobular dentin

Answer 20

• 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

Question 21

what is the tomes granular layer

Answer 21

• 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)

Question 22

what are dead tracts

Answer 22

• 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

Question 23

what is the clinical importance of dentin

Answer 23

• 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

Question 24

what causes tooth sensitivity

Answer 24

• 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

Question 25

how is sensitivity affected with time

Answer 25

- 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

Question 26

when is sensitivity usually experienced

Answer 26

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