DOH114 Study Guide - Midterm Guide: Dentin, Dej, Enam
DOH114
Enamel
-Made by ameloblasts
-Hardest tissue in human body
-Made of hydroxyapatite prisms (96%), 4% organic enamelin
-Prism radiate from the DEJ to the external surface
-Susceptible to acid destruction – critical pH 5.5
-May take up fluoride
-Non vital
-Gnarled enamel: prisms in spiral pattern beneath cusps and IE
-Hunter-Schreger Bands: different layers of prisms reflecting/
transmitting light in different directions
-Complex patterns resist fracture
-Enamel formed incrementally → incremental lines
-Cross striations: right angles
-Enamel striae:
Dentine
-Layer underneath enamel
-Base for enamel, protection for pulp
-Yellow in colour
-Harder than bone, softer than enamel
-Hydroxyapatite crystals 70%
-20% collagen fibres (organic material), 10% water
-Slight flexibility
-Main bulk of the tooth
-Vital and does feel sensations
-Perimeter intertubular peritubular dentine
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Apposition of Dentine
-Process of dentinogenesis
-Primary – initially formed dentine
-Secondary – follows eruption – deposits slowly
-Tertiary (reparative) – responds to pulp stimulation – activates
odontoblasts → laid down rapidly → Irregular appearance
Dentine structure
Structural subcategories:
1. Mantle – (Primary Dentine)
-Thick outer layer
-Covers rest of dentine
-Large collagen fibres
-Deposited at DEJ
2. Circumpulpal – (Primary Dentine)
-Lies beneath mantle
-10 x smaller fibres
-Bulk of primary dentine
3. Globular
-Separates mantle and circumpulpal
-Zone of disturbed dentine formation
4. Predentine
-Nearest to the pulp – non mineralised matrix
-Mineralisation at predentine/dentine junction
Tubules:
All contain fluid filled tubules – cross entire length from pulp to DEJ
-S-Shaped channels – comprise odontoblastic process, dentinal fluid
and axon
-Avascular – nutrition from pulp
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-Larger and closer together at pulpal border
-Intratubular (peritubular) – cuffs surround tubules – hypermineralised
(over mineralised)
-Inertubular – between & around tubules – less calcified
Microscopic features of dentin
-Imbrication lines of von Ebner – incremental lines
-Contour lines of Owen – parallel imbrications lines
-Laid down in 24 hour lots when it is developing
Sensitivity
Sensitivity caused by exposed dentine – many factors contribute:
Loss of enamel
-Attrition
-Abrasion
-Erosion
-Abfraction
Gingival recession
-Ill health – periodontitis, ANUG
-Poor oral hygiene
-Excessive oral hygiene
Mechanisms of sensitivity
-Outstanding theory – hydrodynamic theory –
-Postulates that most pain-evoking stimuli increase fluid flow in
tubules ‘FLUID FLOW PHENOMENON’
-Increased flow → pressure change → receptor activation → nerve
activation
-Different stimuli produce different results
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Document Summary
Made of hydroxyapatite prisms (96%), 4% organic enamelin. Prism radiate from the dej to the external surface. Susceptible to acid destruction critical ph 5. 5. Gnarled enamel: prisms in spiral pattern beneath cusps and ie. Hunter-schreger bands: different layers of prisms reflecting/ transmitting light in different directions. 20% collagen fibres (organic material), 10% water. Secondary follows eruption deposits slowly. Tertiary (reparative) responds to pulp stimulation activates odontoblasts laid down rapidly irregular appearance. Deposited at dej: circumpulpal (primary dentine) Zone of disturbed dentine formation: predentine. Nearest to the pulp non mineralised matrix. All contain fluid filled tubules cross entire length from pulp to dej. S-shaped channels comprise odontoblastic process, dentinal fluid and axon. Larger and closer together at pulpal border. Intratubular (peritubular) cuffs surround tubules hypermineralised (over mineralised) Inertubular between & around tubules less calcified. Imbrication lines of von ebner incremental lines. Contour lines of owen parallel imbrications lines. Laid down in 24 hour lots when it is developing.
