dentine - ioe Flashcards
what is dentine
composite material
apatite crystals on organic scaffold mainly composed of collagen
explain the HAP crystals in dentine
- contain small amnt impurities (carbonate)
- similar shape but smaller than enamels
- 35nm x 10nm
- arranged along + between collagen fibrils
what is the dentine organic matrix
fibrils form a meshwork embedded in an amorphous ground substance
what are the fibrils in dentine organic matrix
- collagen (type I mainly but traces of III + V detected)
- comprise 90% of the matrix
- run parallel to EDJ forming interlacing network perpendicular to odontoblast process
- fibrils in mineralised dentine are larger diameter + more closely packed than predentine
- NOT in bundles
what are the non-collagenous protein in dentine organic matrix
- make up 8%
- dentine phosphoproteins (highly phosphorylated) + dentine matrix protein 1 = actions in mineralisation
- proteoglycans = role in collagen fibril assembly + cell mediated effects (cell adhesion, migration, proliferation, differentiation)
glycoproteins - growth factors (insulin growth factor, bone morphogenic protein, transforming growth factor beta) = released during progress of caries, induce production of reactionary or reparative dentine
what are the lipids in dentine organic matrix
- 2%
- phospholipids, cholesterol and triglycerides
- detected at mineralising front so role in mineralisation
name the a) collagens b) proteoglycans c) lipids d) serum derived proteins e) gylo/sialo proteins f) phosphoproteins g) growth factors of the organic dentine extracellular matrix
a) type 1 (most abundant constituent of matrix), traces of III + V
b) chondroitin 4 sulphate (contains proteoglycans)
c) cholesterol, triglyceride
d) albumin, immunoglobulins
e) osteonectin, dentine sialoproteins, bone sialoprotein, osteopontin
f) dentine phosphoproteins (2nd most abundant constituent of matrix), dentine matrix protein 1
g) insulin growth factor, bone morphogenic protein, transforming growth factor beta
what is the composition of dentine
many small, parallel dentinal tubules in mineralised collagen matrix
65-70% inorganic HAP crystals
20% organic matrix
10% H2O
what physical properties does dentine have
rigid but elastic (not brittle)
so ideal to support overlying enamel due to its elasticity, organic matrix, tubular architecture = greater compressive and flexural strength than enamel
compare the properties of dentine to those of enamel
different but complementary
hardness = e - 296, d - 64
stiffness = e - 131gn/m^2, d - 12gn/m^2
compressive strength = e - 76mn/m^2, d - 262mn/m^2
tensile strength = e - 46mn/m^2, d - 33mn/m^2
where do dentinal tubules run
pulpal surface to enamel-dentine and cementum-dentine junction
tubule branching near enamel-dentine junction
what is the name for dentine between dentinal tubules
intertubular dentine
forms walls of recently formed tubules
what is deposited on walls of dentinal tubules with maturation and what effect does this have
peritubular dentine
narrows their lumens
what are primary curvatures of dentinal tubules
- follow curved sigmoidal course
- convexity of these near the pulp is toward the root
what are secondary curvatures of dentinal tubules
- smaller changes in direction of tubules
what is seen when curvature in adjacent tubules collide and where is this most often
contour line of owen
junction of primary and secondary dentine
what do tubules do in the root and what is this responsible for
terminal part branches + branches loop
appearance of granular layer of tomes between pdl + dentine
to what extent do dentinal tubules taper
2.5um diameter at pulpal end
<1um at EDJ
more widely seperated at their peripheries near EDJ + more tightly packed near pulp bc odontoblasts migrate inward + occupy a smaller surfac as dentinogenesis progresses away from EDJ
tubules in superficial dentine close to edj are smaller + more sparsely distributed than deep tubules
how many tubules in
a) outer dentine
b) inner dentine
per mm^2
a) 20,000
b) 50,000
how do tubules impact permeability of dentine why may this be a problem
make it permeable
- potential for caries + toxins to pass through tubules to the pulp
- occurs if dentine surface exposed (by caries, tooth surface loss, trauma, cavity prep, microleakage at restoration margins)
what is responsible for dentinal tubule formation
odontoblasts (tubules contain their processes)
what type of nerve terminals do tubules contain
afferent
processes of what cells in the peripheral pulp may extend into tubules for a short distance
antigen presenting cells
what is perioblastic and odontoblastic space (from which the process has receded) filled with
extracellular dentinal fluid
what occupies full width of the tubules in predentine and innermost mineralised circumpulpal dentine
odontoblast processes
what happens to no of tubules occupied by odontoblasts processes as we move to outer dentine
decreases
what would we see in a micrograph of transverse section of a tubule
odontoblast process
unmyelinated nerves
what would we see in a TEM of tubules from middle region of coronal circumpulpal dentine
some contain cell processes, some non-cellular material, some empty
when does dentine formation begin
immediately before enamel formation
what is the first step in enamel formation
odontoblasts
lay down extracellular collagen matrix as they begin moving away from future ADJ
what is the second step in enamel formation
gradually following its secretion
mineralisation of collagen matrix facilitated by modification of the collagen matrix by non-collagenous proteins
what is the 3rd step in enamel formation
most recently formed dentine layer (always on pulpal surface)
= PREDENTINE (unmineralised zone of dentine immediately next to odontoblast cell bodies)
what is the 4th step in enamel formation
dentine formation begins
at areas adjacent to cusp tip + progressing to apex of root
contrast dentine formation to enamel formation
dentine formation continues after erruption and throughout life of pulp
what origin is dentine (also dental pulp + cementum)
ECTOMESENCHYMAL
develops from peripheral cells of dental papilla of tooth germ
how is the dentine matrix modified during mineralisation
=odontoblast process role in
a) predentine = secretion of matrix components
b) mineralising dentine = participate in modification of matrix and its mineralisation
what is the rate of deposition of dentine organic matrix
similar to mineralisation
so always layer of unmineralised matrix (predentine) on pulpal surface
what secretes collagen primarily
odontoblast cell body
odontoblast process secretes and what does this form
non-collagenous proteins
complex of collagen and non-collagenous proteins at mineralisation front (between junction of pre and calficied dentine)
what is the role of DPP (non-collagenous protein secreted by odontoblast process)
mineralisation
allows it to bypass some predentine
so odontoblasts are key to
initiating + controlling mineralisation
what happens to calcium transported by odontoblasts
becomes crystalline mineral in dentine by deposition onto a template formed by type 1 collagen fibrils
how does dentine mineralise
same way as bone as mineral crystals added along mineralisation front
different to bone as also combines isolated islands of mineral
what are the isolated islands of mineral that dentine uses to mineralise called and how are they used to mineralise
CALCOSPHERITES
theyre subsumed by mineralising front
what 2 processes are implicated in addition of DPP mediated nucleation on collagen fibrils in initiation of mineralisation
1) mineral crystals (role in initiating mineralisation) develop in matrix vesicles of early mantle dentine
2) calcospherite formation + fusion accounts for irregular appearance of mineralising front
what happens as we move from predentine lining the pulp to the EDJ
mineral content of dentine and thickness of mineral crystals increase
dentine can be divided into zones
what 8 types of dentine exist
1) mantle
2) circumpulpal
3) interglobular
4) pre
5) secondary
6) tertiary
7) reactionary
8) reparative
explain mantle dentine
- at periphery of dentine in crown
- 1st formed
- most peripheral layer beneath the enamel
- special properties help prevent small cracks developing in enamel near the EDJ spreading into dentine
- 5% less mineralised than circumpulpal dentine
- branching of tubules
- fibres oriented perpendicular to EDJ
- appears red when view in polarised light due to different orientation of collagen
explain circumpulpal dentine
- bulk of dentine in the crown + root (between mantle layer + zone of mineralisation)
- uniform in structure except at edges where peripherally integlobular dentine marks incomplete initial mineralisation + centrally the mineralising front represents ongoing mineralisation
- tubular pattern modified on the pulpal surface in older teeth (bc of age related deposition of secondary dentine)
explain interglobular dentine
- outer part of crown (circumpulpal dentine) beneath mantle layer
- incompletely mineralised
- characteristic appearance in ground sections (if signif no of calcospherites dont fuse completely w advancing mineralisation front an area of INTERGLOBULAR DENTINE APPEARS)
- dentinal tubules pass through these areas
- when view ground section in transmitted light = internal reflection of light makes uncalcified interglobular areas appear darker
explain predentine
- unmineralised innermost dentine in crown + root
- where new dentine = deposited through life
- represents initially laid down dentine matrix before its mineralisation
- if demin sections stained w haematoxylin + eosin, it has pale staining appearance bc of diff in matrix composition to mineralised circumpulpal dentine
- mineralising front may show globular OR linear outline reflecting mineralisation process
explain secondary dentine
- innermost layer between circumpulpal + predentine (inner pulpal part of circumpulpal dentine in old teeth)
- continuous w + similar structure to primary dentine
- incd crowding of odontoblasts as it forms throughout life + slower rate of deposition makes its tubular pattern less regular than primary dentine
- laid down as age related change in rate of dentine formation once genetically predetermined thickness of primary circumpulpal dentine is reached / deposited + root length development is complete
- its continuing deposition through life (though not response to external stimuli) contributes to barrier function of dentine
- regular tubular structure
explain tertiary dentine
- inner layer of dentine formed in crown response to serious insult (severe attrition, fracture, caries, cavity prep, microleakage @ restoration margin, trauma)
- its all hard tissue deposited on pulpal surface in response to external stimulus
- found pulpal to circumpulpal (secondary in older teeth) dentine + restricted to region beneath irritation
- its deposition provides barrier to progress of caries / toxins
- stimuli of diff types, presures will be applied to teeth at diff stages in development/aging resulting in response tissue varying in appearance + composition
- regular tubular structure but fewer and irregularly arranged tubules than secondary dentine
- may be ATUBULAR + resemble bone
- signalling molecules in dentine + predentine released by acids (caries) + diffuse through dentine to stimulate activity in og odontoblasts or induce differentiation of stem cells into new odontoblasts
- from it comes reparative and reactionary dentine
explain reactionary dentine
- forms in response to insult where damage is sustained + some odontoblasts die
- existing odontoblasts recover and continue to form dentine (irregular appearance + fewer tubules)
explain reparative dentine
- formed after stimulus where OG odontoblasts in region destroyed and new calcified tissues formed by newly differentiated ‘odontoblast-like’ cells
- much more irregular than circumpulpal
- ‘odontoblast-like’ cells differentiate from stem cell population in absence of epithelial contribution + bioactive molecules for differentiation (cytokines, growth factors) may be locally synthesised and released during inflammatory process accompanying the stimulus
- produced by differentiation of sub-odontoblastic stem cells (replace killed primary odontoblasts)
- tubules less regular + not continuous w those of overlying dentine
what happens in the peripheral region in root dentine
- granular layer of tomes hypomineralised (less than interglobular dentine)
- dentinal tubules branch more + loop back on themselves giving ‘tree-top’ appearance creating air spaces in ground sections that result in internal reflection of transmitted light
what is another explanation for granular appearance
incomplete fusion of calcospherites (smaller than those in crown)
what 2 layers exist in dentine and where
HYALINE = outermost part of root dentine GRANULAR = outer part of root dentine beneath hyaline layer
what are incremental lines and which ones exist in dentine
- arise from incremental deposition of dentine matrix + its subsequent mineralisation
- regular incremental lines
- short-period incremental lines
- long-period incremental lines
explain short-period incremental lines
- VON EBNER LINES
- alternating light + dark bands (each pair reflects diurnal rhythm of dentine formation)
- in cuspal dentine (deposition most rapid) = amount of dentine formed each day and distance between adjacent dark bands = 4um
- root dentin = slower deposition, 2um
explain long-period incremental lines
- associated w changes in collagen fibre orientation
- minor coincident changes in orientation every week (20um) = responsible for these coarser ANDRESEN LINES (run horiztonally, prominenent, 20um spaced lines)
- some may be indistinct
- between each long period line = 6-10 pairs of short period lines giving 6-10 day periodicity
which lines in enamel originate from coincidence of curvatures of dentinal tubules (optical effects)
1) lines associate w primary curvatues of dentinal tubules
- where peaks of sigmoid primary curvatures coincide they form broad bands called SCHREGER LINES (coincident w apex of 1 of primary curvatures)
2) lines associate w secondary curvatues of dentinal tubules
- when secondary curvature in adjacent tubules coincide = give rise to optical effects resulting in CONTOUR LINES OF OWEN
- also seen where theres coincident change in tubular direction (ie junction of primary + secondary dentine)
- NEONATAL LINE between dentine formed before + aft birth
how does peritubular dentine differ from intertubular dentine
lacks collagenous fibrous matrix
5-12% more mineralised (mineral component = mainly carbonated apatite but its crystallite form is distinct from intertubular)
formed at same time or soon after
peritubular dentine constists of
glycoproteins proteoglycan lipids osteonectin osteocalcin bone sialoprotein
where is peritubular dentine found
unerupted teeth
prominent distribution in apical dentine so age change not response tissue
what is present in all peripheral tubules by time primary dentine formation is complete
lining of peritubular dentine that extends from EDJ to within 50-100um of predentine
what proportion of the tissue does peritubular dentine occupy
a) in outer dentine
b) near to predentine
a) 2/3 of its cross sectional area
b) 3%
what is translucent dentine
- w age dentinal tubules (esp in root dentine) become completely occluded by peritubular dentine formation
- contents of tubule acquire same refractive index as intertubular dentine
- when place ground section of a root in h2o (diff refractive index to dentine) regions blocked by peritubular dentine appear translucent while regions w patent dentine tubules fill w h2o appearing opaque
- dentinal tubules become infilled at root apex adjacent to cementum and extend cervically + toward root canal w age
- amount of it incs linearly w age + isnt affected by function or external irritation
- sclerotic dentine = similar function to translucent
what is translucent dentine used for and how
forensic dent
to age teeth (correlation between area of translucent dentine + age)
what are dead tracts in response tissue of dentine
- if primary odontoblasts killed by external stimulus or retract before peritubular dentine occludes tubules empty tubules are left
- can be sealed by their pulpal end by tertiary dentine
- when ground sections prepared + mounted, mounting medium wont enter these sealed tubules + they remain air filled
- transmitted light = totally internally reflected under microscope + these tubules appear as dark dead tracts
what is sclerotic dentine in response tissue of dentine
- when tubules fill in as response to external stimulus they appear transparent
- precipitated material differs from peritubular dentine so its not formed by odontoblast
- mineral = crystalline + maybe apatite, plate like crystal of ectocalcium phosphate reported, large rhomboidal crystals
explain the proposed mechanism of dentine sensitivity
1) direct innervation
2) odontoblasts act as sensory endings
3) hydrodynamics (fluid flow)
explain the hydrodynamics (fluid flow) in dentine sensitivity
1) effective stimulus triggers fluid flow in tubules
2) flow depolarises nerve endings in inner parts of tubules or between odontoblasts at pulp predentine junction
3) from there to subodontoblastic neural plexus
induced response = same whether flow is in or out
explain the pulp dentine complex
dentine = vital tissue bc of presence of odontoblasts
- complex maintains dentine structure, role in innervation of tooth, provides defensive mechanism activated in response to stimulus via formation of tertiary dentine
what is the enamel-dentine junction
- 3D scalloped lines
- evident esp beneath cusps and incisal edges
- crucial to limiting propagation of cracks through tooth + providing resistance to shearing forces
what 4 clinical consideration are associated w dentine
1) caries
2) cavity prep
3) acid etching + bonding to dentine
4) management of discoloured, non vital anterior teeth
explain the clinical consideration of caries
- dentinal tubules provide pathways for ingress of bacteria + their byproducts (so progression diff to in enamel bc of structural diffs)
- once lesion penetrates through enamel, EDJ provides path of least resistance to caries allowing rapid lateral spreading and undermining enamel at cavity margins
- so when prepare cavity ensure EDJ is clear of caries
what are the 3 steps in caries advancement
1) acid demin
2) organic matrix degen + dissolution
3) loss of structural integrity followed by bacterial invasion
caries follows path of dentinal tubules
explain the clinical consideration of cavity prep
- pulp-dentine complex = vital for maintaining tooth - integrity + defense
- when removing carious dentine in deeper lesions using rotary bur must ensure theyre run at slow speed + use tactile feedback to avoid thermal injury to the odontoblasts + pulp and reduce risk of pulp exposure
- if cavity deep in dentine use lining material to seal off patent tubules and protect pulp
explain the clinical consideration of acid etching + bonding to dentine
- adhesion to dentine = more challenging than to enamel bc of
1) high organic + H2O content
2) tubular architecture
3) heterogeneity
4) age changes
5) reactions to caries
6) formation of shear layer when cut using bur - etching exposes collagen fibril network + patent dentinal tubules and surface can be infiltrated by bonding agent forming a HYBRID LAYER sealing surface against leakage
- bonding agent forms resin tags in tubules enhancing retention of restoration BUT weaker bond to dentine than enamel
explain the clinical consideration of management of discoloured, non vital anterior teeth
- neck of tooth may not successfully bleach if root filling not cut back to level well below CEJ following root trtmnt (not necessarily bc pulp dead)
- primary curvature of tubules places their pulpal end lower down than at EDJ
- failure to expose dentinal tubules below level of CEJ on pulpal side hinders penetration of H2O2 bleaching agent into dentine + enamel forming neck of tooth
