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M3: Oral Biology > Dentine > Flashcards

Dentine Flashcards

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1
Q

What is the composition of dentine by weight?

A

Mineral: 70%

Matrix: 20%

Water: 10%

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2
Q

Give some features of dentine:

A
  • 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’’
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3
Q

What direction do the collagen fibres run in dentine?

Where do dentinal tubules run?

A
  • collagen fibres mainly run parallel to ADJ, gives dentine strength
  • dentinal tubules run from ADJ to pulp
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4
Q

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

A

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
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5
Q

What may be in dentinal tubules?

How far do odontoblast processes go through dentine?

A
  • no cell processes, just dentinal fluid
  • odontoblast processes
  • odontoblast processes and nerves

Likely extends approximately 1/3 the way through dentine (inner 1/3)

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6
Q

How many nerves are in dentine at the:

  • pre-dentine
  • inner 1/3
  • outer 2/3

at the pulp horn, cervical margin and root?

A

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

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7
Q

What are the classifications of dentine?

A

Developmental:

  • mantle dentine
  • circumpulpal dentine

Primary, secondary and tertiary

Tubule:

  • peri-tubular or ontra-tubular
  • intertubular
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8
Q

Label and describe some features of these types of dentine:

A

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
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9
Q

What is primary dentine?

Secondary?

Tertiary?

A

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)

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10
Q
A
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11
Q

How is tertiary dentine produced from a mild stimulus?

A strong stimulus?

A
  • 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
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12
Q

Explain reactionary dentine:

Explain reparative dentine:

What is the function of tertiary dentine?

A

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

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13
Q

Where is peri-tubular or intra-tubular dentine found?

Inter-tubular dentine?

A

Peri-tubular:

  • around tubule (lining of tubule)
  • highly mineralised

Inter-tubular:

  • between tubules
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14
Q

Name some other features of dentine:

A

Lines:

  • incremental lines of von Ebner
  • contour line of Owen

Zones:

  • interglobular dentine
  • granular layer of tomes
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15
Q

What are these?

How can they be caused?

A

Tetracycline taken when teeth are developing

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16
Q

What is this?

A
  • coincidence of secondary curvatures
17
Q

What is this and where is it found?

A

Interglobular dentine - failure of calcospherities to fuse

  • commonly found in the crown
18
Q

Where is the granular layer of tomes found?

A
  • on the root, just below the cementum
19
Q

What causes changes in dentine?

A

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

20
Q

What are dead tracts and how do they occur?

What age changes occur with dentine?

A
  • 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
21
Q

What happens when the advancing front of a carious lesion reaches the ADJ?

Advancing front in dentine?

A

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
22
Q

What is the advancing front in dentine?

Zone of bacterial penetration?

Zone of destruction?

A

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
23
Q

What is the 2 zone approach of dental caries in dentine:

A

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
24
Q
A
25
Q

What does the acid do to dentine during bonding?

What is the enxt stage in bonding?

A
  • acid etching dissolves the smear layer and demineralises the hydroxyapatite and leaves the collagen matrix intact
  • use of resin and solvents to penetrate the collagen layer and tubules which forms a hybrid layer, sets solid once light cured, giving a good mechanical bond
26
Q

What is the importance of the hybrid layer?

What is the term wet bonding?

A
  • over-drying of etched dentine results in collapse of the collagen layer
  • this results in reduced bond strengths

Wet bonding: do not overdry conditioned/etched dentine

27
Q

How is the bond strength affected by:

  • caries affected dentine
  • cervical abfraction lesions
  • aged dentine
  • tooth region - depth:
  • smear layer
  • dentine permeability
  • pulpal pressure
A
  • caries affected dentine: bond strength lower
  • cervical abfraction lesions: bond strength 20% lower than normal dentine
  • aged dentine: bond strength shows similar to young dentine
  • tooth region - depth: bond strength reduces as deeper into dentine as less intertubular dentine
  • smear layer: low bond strength
  • dentine permeability: wetness reduces bond strength
  • simulated increased pulpal pressure: decreased bond strength

M3: Oral Biology (5 decks)

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