14. Dentinogenesis Flashcards
Chemical properties of dentine
- 70% inorg - calcium hydroxyapatite crystals
- 20% org - mainly collagen fibrils
- 10% water
Dentine is more or less mineralised than enamel
less
What inorganic matter is in dentine?
- calcium hydroxyapatite crystals (Ca10(PO4)6(OH)2)
- HA crystals appear as uniform small plates between type 1 collagen fibrils
HA crystals form what shape in dentine?
Are these smaller or larger than the ones in enamel?
uniform small plates
smaller
List components of organic matrix in dentine
- collagen fibrils
- proteoglycans
- glycoproteins
- phosphoproteins
- growth factors
What types of collagen are present in dentine?
- mainly 1 - 90%
- 10% 3
- traces of 5 and 6
Proteoglycans in dentine are similar to those in…
bone
3 types of glycoprotein in dentine
- osteonectin
- osteopontin
- dentine sialoproteins
Where else are dentine phosphoproteins found?
- nowhere
- unique to dentine
2 types of growth factors in dentine
- transforming growth factors
- bone morphogenic proteins
Properties of dentine
- softer than enamel
- high tensile strength than enamel
- more resilient/elastic to support brittle enamel
- porous
- sensitive due to pulp innervation
- reactive to damage - repair ability/tertiary dentine
- pulp-dentine complex is living - changes with age
Clinical relevance of dentine properties
- dentine is less radiopaque than enamel to contrast radiolucent pulp
- dentine is resilient/slightly elastic
Dentine formation begins at which point of tooth development?
- late bell stage at cusp tip
Dentine is formed by what cells?
odontoblasts
How does dentine form?
- mesenchymal cells
- differentiate from dental papilla (future dental pulp)
- differentiate when receiving molecular signals from pre-ameloblasts (derived from inner enamel epithelium IEE cells)
Odontoblasts secrete what?
predentine
Explain predentine secreted by odontoblasts
- collagen fibres (type 3) forming von Korff’s fibres at 90 degrees angle to enamel-dentine junction
- begin to secrete smaller type 1 collagen fibrils parallel to EDJ
- secrete matrix vesicles (mv)
Define ‘predentine’
unmineralised area between odontoblast layer and mineralising front
How is mineralising front formed?
- odontoblasts develop cell processes
- initiation of mineralisation with matrix vesicle
- cystallites burst out of vesicle and form the mineralising front
Define ‘matrix vesicles’
- small membrane-covered vesicles produced by odontoblasts and secreted into dentine matrix that surrounds the odontoblasts
Size range of matrix vesicles
25-250 nm
Matrix vesicles contain …
- phospholipids that bind to calcium
- alkaline phosphatase, an enzyme that increases phosphate conc by destroying inhibitor of mineralisation (pyrophosphatase)
Matrix vesicles have been observed during what? What does this mean?
- mineralisation of mantle dentine
- may or may not be involved with mineralisation of circumpulpal dentine ( only seen at mantle)
There is lots/no mineralisation in or near collagen fibres
What does this mean?
- no
- collagen is not responsible for initiating mineralisation
Dentine is first deposited as … and it’s gradually mineralised at …
- predentine
- mineralisation front
Explain predentine thickness
- thickness remains constant as amount that calcifies is balanced by addition of new unmineralised matrix
- during ageing, predentine diminishes in thickness
2 types of dentine mineralisation patterns
- linear
- globular
What determines whether dentine mineralisation is linear or globular?
speed of dentine formation
Where is globular calcification normally found?
- mantle dentine
- where mineralisation occurred in matrix vesicles
In circumpulpal dentine, what kind of dentine mineralisation happens?
- linear or globular
- depends on rate of dentine deposition
- when fast, globular calcification occurs
- slow, mineralisation is gradual and mineralising front looks straight/linear
What happens in globular calcification?
- calcospherites (globular masses of mineralised dentine) form within collagen matrix
- they increase in size using fuse to form a single calcified mass
- if calcification proceeds fast, incomplete fusion of calcospherites can lead to formation of hypomineralised interglobular dentine
Where is interglobular dentine found?
upper third of circumpulpal dentine
Define ‘interglobular dentine’
- leaf-like, hypomineralised areas
- between spheres or globules of mineral
2 adaptations of EDJ to role
- crater-like depressions to increase surface area of EDJ
- sharp edges to help attachment of enamel to dentine
Enamel spindles are formed from an … that has intercalated between two … and extends into the …
- odontoblast process
- ameloblasts
- enamel
What is seen in mantle dentine?
branched tubules
Mantle dentine is the … layer of …
outermost
crown dentine
Hyaline layer is the outermost layer of …
root dentine
Why are there S-shaped tubules in the coronal region of the crown?
- due to crowding of odontoblasts
- they are pushed apically as dentine grows inwards towards pulp
Why are there linear shaped tubules in cervical region of crown?
- beneath cusps/incisal edges/root dentine
- little or no crowding of odontoblasts
There are … shaped tubules in coronal region of crown but … shaped in cervical region
S
linear
Define ‘secondary curvature in dentinal tubules’
- slightly changes in tubule direction in dentine deposition
- creates wavy dentinal tubules
2 types of incremental growth lines
- von Ebner lines
- Andresen lines
Explain von Ebner lines
- dentine deposited daily, forming daily lines
- lines 3-4 micrometres apart (less than 2 near root surface)
- equivalent to cross striations in enamel
- less defined with closer spacing
Explain Andreson lines
- long period growth lines
- lines 20 micrometres apart (around 6-10 von Ebner lines)
- equivalent to striae of Retzius in enamel
- more sharply defined with wider spacing
What happens when secondary curvature is pronounced and coincides in adjacent tubules?
- contour line of Owen forms
- caused by metabolic stress/disturbances during dentine formation
- these lines are accentuated growth lines (Von Ebner) and hypomineralised
What is the most prominent incremental growth line?
- neonatal line
- due to disturbances of dentine formation by birth process
How is an Owen line produced and what does it represent?
- bending of dentinal tubules
- reflects a disturbance in dentine formation (like the accentuated lines in enamel)
2 ways to classify dentine
- by time of development
- anatomical location/histology
4 divisions of dentine under ‘time of development’ class
- predentine
- primary dentine
- secondary dentine
- tertiary dentine
Predentine is an … dentine …
- unmineralised
- matrix
Primary dentine forms when?
during tooth development
Secondary dentine forms when?
after root completion
Tertiary dentine forms when?
in response to stimulus to repair
2 divisions of dentine within anatomical location/histology
- coronal dentine
- root dentine
Types of coronal dentine
- mantle dentine (outermost layer of crown dentine)
- circumpulpal dentine (forms bulk of crown) split into interglobular, intetubular and intratubular dentine, sclerotic dentine
Which forms first? Mantle/cicumpulpal dentine?
mantle
When does ‘interglobular dentine’ form?
when dentine is mineralised rapidly
Where does intertubular dentine form?
between dentinal tubules
Alternative name for intratubular dentine
peritubular dentine
Where does intratubular dentine form?
inside dentinal tubules
When does sclerotic dentine form?
- caused by complete obliteration of dentinal tubules
Explain root dentine
- hyaline layer is outermost of root dentine
- granular layer of Tomes below hyaline layer
- intertubular, intratubular and sclerotic dentine
Primary dentine is all dentine formed until …
completion of the root formation
Secondary dentine forms after …
Over time, it reduces …
- completion of root formation
- size of pulp chamber and root canals
Tertiary dentine is produced in response to …
external stimuli
- attrition, caries, cavity prep etc
- for tooth repair and protection2
2 types of tertiary dentine
- reactionary
- reparative
Define ‘reactionary dentine’
- when original odontoblasts continue to function in dentine deposition
- contains less dentinal tubules
- formed after weak stimuli/injury for a slow response
Define ‘reparative dentine’
- when original odontoblasts die, newly recruited odontoblast-like cells begin depositing dentine
- these are induced from pulp stem cells
- less structured in response to severe injury/stimuli for a fast response
In secondary dentine, there is a visible change in what?
- direction of dentinal tubules
Secondary dentine is the normal continuation of…
dentine formation occurring throughout life
- by odontoblasts lining pulp and root canals
Secondary dentine forms a regular/irregular distribution?
- irregular
- mostly on roof and floor of pulp chamber
Explain intratubular dentine
- forms within dental tubule and lines inner surface
- hypermineralised (40% more than surrounding dentine)
Explain intertubular dentine
- between dental tubules
- in any primary or secondary dentine
- less mineralised than intratubular dentine
Tubule space appears …, ringed with …
- black
- white highly-mineralised intratubular dentine with grey intertubular dentine between
Demineralisation of tooth completely removes …
What does this mean?
- intratubular dentine
- leaves an intratubular space making tubule appear wider separated only by intertubular dentine
Define ‘sclerotic dentine’
- continued formation of intratubular dentine leading to obliteration of tubules
- once completed, termed sclerotic
Sclerotic dentine appears … in ground sections
Why?
- transparent
- increased mineralisation
Sclerotic increases with … Why?
- age
- in areas of attrition and caries of enamel
- protects pulp against invading microorganisms
Define ‘dead tracts’
- when dentinal tubules have lost their odontoblast processes following death of odontoblasts or retraction of processes
- tubules become empty and air filled
- appears as dark bands in ground sections termed dead tracts
2 explanations for Tomes granular layer
- extensive branching and backward looping of odontoblast processes
- incomplete fusion of calcospherites (like interglobular dentine)
