Dentin Flashcards
structural components of dentin
Ø 70% Mineral
• Calcium Hydroxyapatite [Ca10(PO4)6(OH)2]
• Trace amounts of calcium carbonate, fluoride,
magnesium and zinc
Ø 20% Organic
• Type I collagen with trace amounts of type III and V
• 50% of noncollagenous proteins are phosphoprotein
• Sialoprotein and sialophosphoprotein
• Proteoglycans and glycosaminoglycans
• Osteonectin and osteopontin
Ø 10% Water
collagen of dentin differences from bone
Ø The type I collagen of dentin is slightly different
than that of bone.
• Higher ratio of proline and hydroxyproline
• Higher prevalence of molecular cross-linking
• Higher level of bound water
• Random orientation of the hydroxyapatite crystals
other proteins of dentin (Non-collagenous)
non-collagenous proteins include: Ø Proteoglycans • Biglycan • Decorin Ø Glycosaminoglycans • Chondroitin-4- sulfate • Chondroitin-6- sulfate Ø -carboxyglutamate-containing protein (Gla-proteins) Ø Osteonectin Ø Osteopontin • Contains the receptor binding sequence Arginine-Glycine-Asparagine (RGD binding complex)
odontoblast life cycle stages
Pre-odontoblast
Secretory Odontoblast
Transitional Odontoblast
Resting Odontoblas
Stimulus for ectomesenchymal cell differentiation into pre-odontoblasts?
Stimulus for ectomesenchymal cell differentiation
into pre-odontoblasts appears to be derived from
fibronectin located within the basal lamina of the
inner enamel epithelium (IEE) – and several
growth factors derived from the IEE.
will express receptor for fibronectin and bind to IEE
pre odontoblast differentiation
Ø Pre-odontoblastic fibronectin receptors all the cells
to align themselves along the basal lamina, assume
polarity, and differentiate into secretory cells.
bind fibronectin
Growth factors secreted by the IEE that play a roll in odontoblast differentiation include:
- Transforming Growth Factor (TGF)
- Bone Morphogenetic Protein (BMP)
- Insulin-like Growth Factor (IGF)
- Fibroblast Growth Factor (FGF)
complete dif of odontoblasts req?
Complete differentiation requires a set number of
cell divisions which allows cells to express
appropriate receptors able to bind growth factors
localized to the IEE basal lamina.
must undergo several divisions in order to recognize the GFs
last mitotic division of pre-odontoblast produces?
The last mitotic division results in a mature odontoblast that can recognize all req factors
also produces daughter cell that is forced into the subodontoblastic cell layer.
cells of the subodontoblastic layer, purpose?
Cells in the subodontoblastic layer, because they are
removed from the sphere of influence of the IEE, represent
ectomesenchymal cells exposed to the entire cascade of
developmental controls for odontoblastic differentiation
except for the inductive influence of the growth factors
associated with the IEE> cannot produce dentin
It is thought that this cell population is responsible for the reparative odontoblasts that differentiate from pulpal cells due to exposure to GFs upon destruction of the odontoblasts above them
secretory odontoblasts
shape
secrete?
Ø Tall columnar cells (50 μm) with extensive
junctional complex and gap junction formations.
Ø Exhibit significant alkaline phosphatase activity.
Ø Secrete type I and traces of type III and V collagen.
Ø Secrete matrix vesicles=req for mineralization
mantle dentin
components?
fiber arrangment?
50-100 μm thick layer of first formed dentin.
Matrix consist of both type I and III collagen.
Collagen fibers in matrix are arranged perpendicular to the basal lamina of the IEE.
rates of dentin deposition
The organic matrix of dentin is deposited incrementally at a rate of 4 m to 8 m per 24 hours.
Incremental lines in dentin (lines of von Ebner) are thought to represent a hesitation in matrix formation and subsequently altered mineralization that occur after 4-20 days of matrix deposition, these areas ore hypomineralized
deficencies and irregularities of dentinogenesis appearence
Deficiencies and irregularities in dentinogenesis, resulting
in areas of hypomineralization, are common and appear as
accentuated incremental lines (e.g., neonatal line, contour
lines of Owen) or areas of interglobular dentin.
dentin tubules shapes
Dentinal tubules are tapered:
• 2.5 μm diameter at the pulpal surface
• 1.2 μm diameter at midlength
• 0.9 μm near the DEJ
peritubular and intertubular dentin
peritubular dentin lines the tubule and is more mineralized (more exposure to the secretory vesicles)
intertubular dentin is less mineralized
significance of dentin tubule shape
Because of decreasing volume of the pulp
chamber, the number of dentinal tubules per
unit area at the pulpal surface is 40,000/mm2
and about ½ that number of the DEJ.
odontoblastic process branching
towards the basal lamina (DEJ) thes can branch considerably
placement for composite resin restorations
Positive impression of branching and anastomosis of dental
tubules by flowing composite bonding agent onto an acid
etched surface of dentin as would be done in placement of a
composite resin restoration.
patterns of dentin mineralization
linear: uniform calcification
globular: some areas more/less mineralized (interglobular dentin), spotty minerlization
interglobular dentin
A zone of globular, rather than linear,
formed dentin in the crowns of teeth. Characterized by
interglobular spaces that are unmineralized or hypomineralized
dentin between normal calcified dentinal layers.
Tome’s granular layer
A granular-appearing layer in the dentin of the root adjacent to the cementum.
Possibly comprised of hypomineralized interglobular dentin formed due to globular dentin minerlization
primary dentin
All dentin (except mantle dentin) formed up to the time the tooth achieves functional occlusion.
secondary dentin
All dentin formed (except tertiary dentin)
formed after tooth achieves functional occlusion.
dead tracts
Dentinal tubules that are void of the odontoblastic process.
They are generally filled with air or organic debris and
look black in transmitted light microscopy.
sclerotic dentin
Dentin in which the tubules are occluded with mineral due to aging
The dentin is non-tubular and is nearly transparent.
Incidence of occurrence increases with increasing age of the patient.
May also be tertiary (reparative) dentin.
Incremental Lines of von Ebner
Lines of von Ebner occur after 4-20 days of matrix
deposition and are thought to represent hesitations in matrix
deposition and therefore altered mineralization.
Neonatal Line and Contour Lines of Owen
Both represent exaggerated lines of von Ebner that occur during periods of altered cell metabolism.
Rx that can stain dentin?
tetracycline
affects part of tooth developing at the time of Rx
intrinsic stain
Tertiary Dentin (a.k.a. Reparative Dentin): why formed?
Dentin deposited by newly differentiated odontoblasts at the site of pulpal trauma> subodontoblastic cells
A defensive reaction attempting to wall off the pulp from the site of injury (e.g., caries).
pulp capping
can be done to protect the pulp/ prevent root canals
insult the pulp to induce tertiary dentin formation= can form bridge of reparative dentin
formation of tertiary dentin
Cells in the subodontoblastic layer, once exposed to
growth factors released by stimulated pulpal cells
differentiate and form the matrix of reparative dentin.
• Bone Morphogenetic Protein (BMP)
• Insulin-like Growth Factor (IGF)
• Fibroblast Growth Factor (FGF)
• Dentin Matrix Protein (DMP)
dentinogenesis imperfecta
pulp chambers/canal?
Hereditary defect
bluish-gray teeth with an opalescent sheen.
The enamel is normal but chips off due to lack of support by the abnormal dentin. Lack of tuftelin at the DEJ, no enamel tufts
The pulp chamber and canals are generally obliterated by defective dentin formation.
Attrition
Loss by wear of surface caused by tooth to tooth
contact during mastication or parafunction.
Matching wear on occluding surfaces, and shiny facets on amalgam contacts are common.
Enamel and dentin wear is at the same rate.
Possible fracture of cusps or restorations reparative dentin may form to protect the pulp chamber
erosion
Loss of hard dental tissue by chemical processes.
Broad concavities, with cupping of occlusal surfaces and dentin exposure.
Incisal translucency as well as wear on non-occluding surfaces.
Amalgam restorations appear “raised“ and have a non-tarnished appearance.
Patients are usually hypersensitive.
Very common with GERD patients.
hydroxyapatite weakness
Many hydroxyapatite crystals exhibit a core of a
relatively more soluble carbonate apatite.
The carbonate substitution in the lattice structure of
enamel occurs primarily at phosphate sites.
The core of carbonated apatite is eroded preferentially
by acids due to its greater susceptibility to dissolution
flouride strengthening
Fluoride may substitute for hydroxyl ions in
hydroxyapatite, conferring greater stability and
resistance to acidic dissolution.
bacteria responsible for caries, regions
Ø S. mutans (enamel/dentin caries) Ø S. sorbrinus (enamel/dentin caries) Ø S. gordonii (enamel/dentin caries) Ø L. acidophilus (enamel/dentin caries) Ø Actinomyces viscosus (root caries)
caries as they reach the dentin
As the process of dental caries (acid dissolution of the enamel) reaches the DEJ, it spreads laterally (due to the branching of dentinal tubules at the DEJ/ weaker dentin) and then penetrates towards the pulp within the dentinal tubules.
A substantial cavitation is produced beneath the adjacent enamel surface.
Initially, the caries lesion exhibits a small opening or orifice in the enamel and pyramidal shaped dentin lesion with the apex of the pyramid pointing towards the tooth pulp.
places of debris retention for caries, solution?
grooves and pits
sealant to reduce the build up
balancing act of caries
balance between pathological and protective processes
caries form when the pathological outweighs the protective
dentinal sensitivity
how many people?
most affected teeth?
stimuli?
1 in 5 adults suffers from dentinal sensitivity.
Ø The teeth most commonly affected are cuspids
and bicuspids.
Ø Stimuli associated with dentinal sensitivity include:
• Cold and/or hot beverages
• Sweet or sour (acidic) foods or beverages
• Overly aggressive brushing
• Acidogenic plaque bacteria
• Cosmetic bleaching of teeth
• Clenching or bruxism
theories of sensitivity
Direct Innervation Theory
Transduction Theory
Brännström’s Hydrodynamic Theory
Direct Innervation Theory
• Direct stimulation of nerve endings in dentinal tubules
Transduction Theory
• Stimulation of odontoblasts that are coupled to nerves
in the pulp
Brännström’s Hydrodynamic Theory
This theory has roots in Charles’ Law:
• The volume of a gas (or fluid) is directly proportional
to the amount of heat applied at a constant pressure
• If heat is applied to a sensitive tooth, the volume
of the fluid in the tubules increases, causing
stimulation of the nerve endings. Cold would
have a similar effect, as the volume of fluid
would decrease, still causing a movement in the
fluid, and stimulation of the nerve endings
contents of secretory vesicles for odontoblasts
Ø Secrete matrix vesicles=req for mineralization • Phospholipids • Alkaline phosphatase • Phosphoproteins • Pyrohosphatase • Ca ++ and PO4- • Annexin § mediates flow of Ca++ into the matrix vesicle. Also serves as a collagen receptor that binds matrix vesicles to collagen. • Calcium hydroxyapatite crystallites
