Dentin Flashcards
Dentin (Structural Components) (3)
70% mineral
20% organic
10% water
70% Mineral (2)
• Calcium Hydroxyapatite [Ca10(PO4)6(OH)2]
• Trace amounts of calcium carbonate, fluoride,
magnesium and zinc
20% Organic (5)
- 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
The type I collagen of dentin is slightly different than that of bone. (4)
- Higher ratio of proline and hydroxyproline
- Higher prevalence of molecular cross-linking
- Higher level of bound water
- Random orientation of the hydroxyapatite crystals
Dentin matrix non-collagenous proteins include: (5)
Ø Proteoglycans Ø Glycosaminoglycans Ø -carboxyglutamate-containing protein (Gla-proteins) Ø Osteonectin Ø Osteopontin
Proteoglycans (2)
- Biglycan
* Decorin
Glycosaminoglycans (2)
- Chondroitin-4- sulfate
* Chondroitin-6- sulfate
Osteopontin (1)
• Contains the receptor binding sequence Arginine-Glycine-
Asparagine (Arg-Gly-Asp or a.k.a. the RGD binding complex)
Life Cycle Stages (4)
Pre-odontoblast
Secretory Odontoblast
Transitional Odontoblast
Resting Odontoblast
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.
Pre-odontoblastic fibronectin receptors all the cells
to (3)
align themselves along the basal lamina,
assume polarity, and
differentiate into secretory cells.
Growth factors secreted by the IEE that play a roll
in odontoblast differentiation include: (4)
- Transforming Growth Factor (TGF)
- Bone Morphogenetic Protein (BMP)
- Insulin-like Growth Factor (IGF)
- Fibroblast Growth Factor (FGF)
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.
The last mitotic division results in a
mature odontoblast
and a daughter cell that is forced into the subodontoblastic
cell layer.
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. It is thought that this cell
population is responsible for the reparative odontoblasts that
differentiate from pulpal cells.
Dentin (The Secretory Odontoblast) (3)
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.
Dentin (The Secretory Odontoblast):
secretes (7)
- Phospholipids
- Alkaline phosphatase
- Phosphoproteins
- Pyrohosphatase
- Ca ++ and PO4-
- Annexin
- Calcium hydroxyapatite crystallites
• Annexin
mediates flow of Ca++ into the matrix vesicle. Also serves as
a collagen receptor that binds matrix vesicles to collagen.
Mantle Dentin:
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.
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.
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.
Dentinal tubules are tapered: (3)
- 2.5 μm diameter at the pulpal surface
- 1.2 μm diameter at midlength
- 0.9 μm near the DEJ
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.
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.
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. 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:
The organic matrix of
dentin is deposited in increments of 4 μm to 8 μm per 24
hours. 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.
Tertiary Dentin (a.k.a. Reparative Dentin):
Dentin deposited
by newly differentiated odontoblasts at the site of pulpal
trauma. A defensive reaction attempting to wall off the pulp
from the site of injury (e.g., caries).
Cells in the subodontoblastic layer, once exposed to
growth factors released by stimulated pulpal cells
differentiate and form the matrix of reparative dentin. (4)
- Bone Morphogenetic Protein (BMP)
- Insulin-like Growth Factor (IGF)
- Fibroblast Growth Factor (FGF)
- Dentin Matrix Protein (DMP)
Dentinogenesis Imperfecta:
Hereditary defect that results in
bluish-gray teeth with an opalescent sheen. The enamel is
normal but chips off due to lack of support by the abnormal
dentin. 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
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.
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
— may substitute for hydroxyl ions in
hydroxyapatite, conferring greater stability and
resistance to acidic dissolution.
Fluoride
Bacteria responsible for dental caries include: (5)
Ø Streptococcus mutans (enamel/dentin caries)
Ø Streptococcus sorbrinus (enamel/dentin caries)
Ø Streptococcus gordonii (enamel/dentin caries)
Ø Lactobacillus acidophilus (enamel/dentin caries)
Ø Actinomyces viscosus (root caries)
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) 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.
– adults suffers from dentinal sensitivity.
1 in 5
Dentinal Sensitivity
The teeth most commonly affected are
cuspids
and bicuspids.
Stimuli associated with dentinal sensitivity include: (6)
- 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
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
• Stimulation of dentinal tubules or exposed
odontoblastic cell processes causes movement of
tissue fluids within dentinal tubules that, in turn,
stimulates nerve endings in close association with
dentin at the dentin/pulpal interface.
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
