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
2
Q
what is the ectodermal origin
A
- from dental papilla - mesenchyme
3
Q
is dentin living tissue
A
- odontoblasts and intercellular substance
- dentin production continues life of tooth
4
Q
what is the elasticity like in dentin
A
- can flex better than enamel
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
6
Q
what is the colour of dentin
A
- yellow in colour – clinical colour of tooth
7
Q
what is the chemical composition of dentin
A
- 70% inorganic hydroxyapatite
- 30% organic and water - ground substance and collagen fibres and protein
8
Q
what are 3 distinct microscopic areas of dentin
A
- dentinal tubule
- peritubular dentin
- intertubular dentin
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
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
11
Q
what is intertubular dentin
A
- 2nd hardest
- makes up bulk of dentinal material (between tubes holding them together)
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
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
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
15
Q
what are the 3 types of dentin
A
- primary dentin
- secondary dentin
- tertiary dentin (two types: reparative dentin and sclerotic dentin)
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
