Dentine Flashcards
What is the composition of dentine by weight?
Mineral: 70%
Matrix: 20%
Water: 10%
Give some features of dentine:
- specialised connective tissue
- hard (KHN 75)
- strong and resilient
- ~70% mineral - hydroxyapatite
- ~20% organic - collagen
- '’porous biological composite of apatite crystals in a collagen matrix’’
- '’fibre reinforced biological composite’’
What direction do the collagen fibres run in dentine?
Where do dentinal tubules run?
- collagen fibres mainly run parallel to ADJ, gives dentine strength
- dentinal tubules run from ADJ to pulp
How many tubules per mm2 are found at the ADJ?
At predentine?
What is the diameter at these different places?
List features of deep dentine
ADJ - 15,000-20,000, diameter 0.5-1 micron
Predentine - 45,000-65,000, diameter 2.0-3.0 microns
Deep dentine is:
- more porous
- wetter
What may be in dentinal tubules?
How far do odontoblast processes go through dentine?
- no cell processes, just dentinal fluid
- odontoblast processes
- odontoblast processes and nerves
Likely extends approximately 1/3 the way through dentine (inner 1/3)
How many nerves are in dentine at the:
- pre-dentine
- inner 1/3
- outer 2/3
at the pulp horn, cervical margin and root?
Pulp horn:
- pre-dentine 27-85%
- inner 1/3 10%
- outer 2/3 0%
Cervical margin:
- 7%, 2%, 0%
Root:
- <7%, 0%, 0%
Most nerves in pre-dentine/inner dentine in pulp horns
Less at cervical margin - clinically a sensitive area
What are the classifications of dentine?
Developmental:
- mantle dentine
- circumpulpal dentine
Primary, secondary and tertiary
Tubule:
- peri-tubular or ontra-tubular
- intertubular
Label and describe some features of these types of dentine:
Mantle dentine:
- 1st formed dentine - adjacent to enamel
- ~150 microns thick
- characterised by large collagen fibrils at 90 degrees to ADJ, slightly less mineralised by ~5%
Circumpulpal dentine:
- rest of dentine
- collagen fibrils closely packed and interwoven, parallel to ADJ
What is primary dentine?
Secondary?
Tertiary?
Primary dentine: formed during tooth development (upto root completion ~2-3 years after eruption)
Secondary dentine: formed after root completion, forms slowly throughout life of the tooth (root canals get smaller with age)
Tertiary dentine: forms in response to pulpal insult (e.g. caries, restorations)
How is tertiary dentine produced from a mild stimulus?
A strong stimulus?
- mild stimulus e.g. slowly progressing caries, causes odontoblasts to react and produce preactionary tertiary dentine
- strong stimulus can kill off odontoblasts, so pulpal stem cells can differentiate into cells to make a dentine like structure - reparative tertiary dentine
Explain reactionary dentine:
Explain reparative dentine:
What is the function of tertiary dentine?
Reactionary:
- uses existing odontoblasts
- slow formation
- tubular structure
Reparative
- existing odontoblasts destroyed
- recruit newly differentiated ‘odontoblasts’
- rapid formation
- poor structure
Function: remove pulp from stimulus
Where is peri-tubular or intra-tubular dentine found?
Inter-tubular dentine?
Peri-tubular:
- around tubule (lining of tubule)
- highly mineralised
Inter-tubular:
- between tubules
Name some other features of dentine:
Lines:
- incremental lines of von Ebner
- contour line of Owen
Zones:
- interglobular dentine
- granular layer of tomes
What are these?
How can they be caused?
Tetracycline taken when teeth are developing
What is this?
- coincidence of secondary curvatures
What is this and where is it found?
Interglobular dentine - failure of calcospherities to fuse
- commonly found in the crown
Where is the granular layer of tomes found?
- on the root, just below the cementum
What causes changes in dentine?
Dentine changes in response to insult
- tertiary dentine
- Sclerosis: tubules blocked off, appears transparent
Sclerosis in outer 1/3 of dentine
Tertiary dentine near pulp
What are dead tracts and how do they occur?
What age changes occur with dentine?
- odontoblasts die
- empty tubules sealed with reparative tertiary dentine
- appear dark
- can occur under normal cusp tips - odontoblasts overcrowding
Secondary dentine - reducing size of pulp chamber
Translucent sclerotic dentine:
- tubules occluded with calcified material
- progresses cervically from apex
- forensics - help age teeth
- clinically - more peritubular dentine, root less flexibile so fracture risk for extraction
What happens when the advancing front of a carious lesion reaches the ADJ?
Advancing front in dentine?
Advancing front reaches ADJ:
- sclerotic dentine as tubules become blocked off, and forms early reactionary tertiary dentine
Advancing front in dentine:
- cavitation, demineralisation losing surface layer and bacteria penetrates into lesion
What is the advancing front in dentine?
Zone of bacterial penetration?
Zone of destruction?
Advancing front:
- zone of demineralised dentine
- acid demineralisation, no bacteria
Zone of bacteria penetration:
- bacteria in tubules
- lateral spread via branched tubules
Zone of destruction:
- mixed bacterial population
- proteolytic enzymes
- destroys organic matrix
What is the 2 zone approach of dental caries in dentine:
Outer, superficial zone:
- highly infected
- irreversibly demineralised dentine
- proteolytic degradation of collagen matrix
Inner, deeper zone:
- dentine has been reversibly attacked
- collagen matrix not severely damaged
- minimally infected
- potential for repair
