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What is the clinical important of the high density of dentinal tubules at the EDJ?

If carious legion breaches EDJ can cause large amount of damage do dentine even if relatively small


Describe intertubular dentine

Fills gaps between tubules
Relatively less mineralised but greater collagen composition than peritubular
T1 collagen fibres arranged perp. to tubules and more loosely distributed


Describe peritubular dentine

Dentine that lines inside of tubules
Lack collagenous fibrous matrix but more mineralised so appears more radiopaque
Present in unerupted teeth


What can form translucent dentine?

Occluding of dentinal tubules by peritubular dentine


Name the 4 layers of dentine

1. Predentine
2. Hyaline and granular layers
3. Circumpulpal
4. Mantle


What is mantle dentine?

First formed dentine of crown


Describe circumpalpul dentine

Forms bulk of dentine
Uniform in structure except: inner surface interglobular; outer mineralisation front

Tubules modified w/ age by: 2ndary dentine deposition in pulp, disease, tertiary dentine/sclerotic dentine deposition


Describe the hyaline and granular layers

First formed dentine of root, present on periphery of root
Hypomineralised compared to circumpalpul
Tubules branch more and loop back creating air spaces
Internal reflection of transmitted light


Describe interglobular dentine

Found in crown just below mantle dentine and in root in granular layer of tomes

Area of less calcified areas of dentine, appear as irregularly shaped crescents
Result of uneven fusion of mineralisation front causing little calcification

Tubules pass through but peritubular dentine absent


Describe predentine

First layer of dentine, unmineralised
Innermost layer
Mineralisation front globular or linear
Thicker in younger teeth


Describe the process of mineralisation of dentine

Organic matrix laid down
Ca2+ transported through odontoblasts to area of calcification
Ca2+ crystallises in dentine after deposition on collagen fibrils
Matrix deposition and mineralisation continue, zone of calcification usually visible


Compare linear and globular mineralisation

Linear: apposition on pre-calcified areas
Globular: small, spherical areas become larger, fuse w/ each other


What are Von Ebner lines?

Perpendicular (to dentinal tubules) lines along tubules caused by daily alterations in formation of dentine


Describe primary dentinogenesis

All dentine up till eruption
May become translucent w/ age due to inc. deposition of peritubular occluded tubules


Describe secondary dentinogenesis

Dentine after eruption
Structurally similar to primary but w/ fewer tubules
Will red. pulp chamber and root canal size in time


Describe tertiary dentinogenesis

Produced in response to stimuli such as damage/irritation to overlying dentine/enamel
Irregularly shaped and few dentinal tubules
W/ ageing/severe damage can obliterate pulp cavity


Describe sclerotic dentine

Produced in response to external challenge (caries)
Appears translucent due to inc. mineralisation
Tubules filled to block ingress of bacteria (protect pulp)


What are dead tracts?

Empty dentinal tubules due to odontoblast death or retraction process


What are the 3 clinical implications of dentine?

1. Permeability
2. Response to external stimuli
3. Sensitivity


Why is permeability of dentine of clinical significance?

When exposed, substances from external environment can reach pulp through dentinal tubules resulting in pulpitis


Explain the clinical relevance of external stimuli response of dentine

If stimuli not strong enough to destroy pulp can induce production of tertiary dentine as protective measure - eventually obliterate pulp


Explain why sensitivity of dentine is relevant

Exposed dentine is v painful: dentinal fluid compresses nerve endings on dentinal tubules


What are the 3 theories of dentine sensitivity?

1. Direct innervation
2. Hydrodynamic
3. Transduction


What is the role of the supporting apparatus?

1. Protect teeth from masticatory forces
2. Prevent premature loss of teeth


Describe the thickness of cementum

Thinner coronally: 0.05-0.1mm
Thicker apically: 0.2-1mm


What are the 2 functions of cementum?

1. Cover dentine
2. Provide attachment of tooth to PDL


What are some of the characteristics of cementum?

Pale yellow, dull surface
Inner surface: firmly attached to dentine
Outer: adjacent to PDL
Clean surface is hard, has 'glass-like' texture
Meets enamel at CEJ


Describe the mineral and organic composition of cementum

Mineral: mainly Ca, PO4 in HA crystals
Organic: mainly collagen, various glycoproteins and proteoglycans


Describe some of the physical and chemical properties of cementum

Similar to bone but: avascular, no innervation and less readily resorbed

Softer than dentine, more permeable
Cellular type is more permeable than acellular type
Permeability dec. w/ age


What are the 2 ways in which cementum can be classified?

1. Cell component
2. Collagen component