dentine structure Flashcards
composition of dentine
• 70% Inorganic ○ mainly Hap & some non-crystalline amorphous CaPO4 • 20% Organic ○ 90% collagen ○ non collagenous matrix proteins ○ lipids • 10% water
characteristics of dentine
• Hard ○ can be distinguished on radiographs ○ Caries are identified as dark regions • Elastic property ○ good support for enamel • Yellow in colour ○ discoloured when non-vital
how many types of dentine are there and what are their characteristics??
3 types
Primary dentine
• Made during tooth development • Forms most of the tooth ○ Outer layer: § first formed mantle dentine (20mm thick) ○ Main bulk: § circumpulpal dentine
Secondary dentine
• Dentine laid down post eruption • Formed after root formation completed & tooth functional • Continues at slower rate • Similar structure to primary dentine • Deposition not always even around pulp chamber ○ in molars, more on roof & floor of pulp chamber ○ decrease in size of pulp chamber – pulp recession in cavity preparation in young patients greater risk of exposing pulp
Tertiary dentine
• Can be reactionary or reparative dentine • Produced in response to noxious stimuli ○ caries, abrasion (eg toothbrush), attrition • Only formed by odontoblasts directly affected by stimulus ○ structure depends on intensity and duration ○ weak – normal appearing dentine ○ strong – quicker, very dysplastic, irregular tubules
when aging, how does dentine change to affect the pulp?
secondary dentine gradually occludes the pulp
pulp becomes a more narrow channel
pre-dentine characteristics
- Newly / freshly formed dentine
- Unmineralised
- Secreted by odontoblasts as organic matrix
- Undergoes remodelling to allow for mineralisation
- Mineralisation occurs at the mineralisation front
how does reparative dentine form?
- Stem cell population recruited from the pulp
- Migrate to site of injury
- Differentiate into odontoblast-like cells
- Secrete new reparative dentine matrix
role of tertiary dentinogenesis
increases distance between injurious agent & pulp cells
helps restore structural integrity of tooth
if uncontrolled, can reduce pulpal vitality
restorative materials can affect pulp how
cellular toxicity
inflammation
tertiary dentinogenesis : reactionary vs reparative
how does carious dentine look in histology
bacterial observed within tubules
stains darkly
why are tubules S shaped - curved
due to odontoblast crowding as they move towards pulp
at the ends of the dentine tubules there is _____
• Terminal branching
○ Gives permeability to dentine
§ Good for elasticity and ability to supply nutrients
§ Not good for caries process
§ Can become occluded
□ By age, pathlogy or as a protective mechanism of the tooth
□ sclerotic dentine & dead tracts
what is peritubular dentine
• Hypermineralised zone surrounding tubules
○ rich in matrix proteins, few collagen fibres
○ Mostly calcium phosphate and hydroxyapatite
Only seen in mineralised dentine not pre-dentine
what is sclerotic dentine
• Dentinal tubules that have become occluded
• Continued secretion of peritubular dentine (PTD).
• Normal feature of ageing process
○ slow rate, decreases permeability of dentine
• Decrease in size of tubule lumen
• Transparent glassy appearance – sclerotic dentine
Deposition of mineral within tubule without dentine secretion (consequence of demineralisation & caries?)
what is intertubular dentine?
• Network collagen fibres embedded in ground substance in which hydroxyapatite crystals deposited – bulk of dentine!
• Collagen
○ type I, very insoluble (stable), random meshwork
• Ground substance
○ plasma proteins
○ PGs / GAGs – structural role
○ phosphoproteins – role in nucleation (anionic)
○ tissue specific proteins (osteocalcin) regulatory role
○ growth factors
what is globular and interglobular dentine?
• Globules made up of Hap crystals • If fail to fuse get areas of hypocalcified / uncalcified dentine ○ interglobular dentine ○ Areas of weakness in the tooth § Risk for caries
