Week 4 - Dentin Flashcards
What three things are dentin made of?
70% Mineral
20% organic
10% water
What minerals is dentin made of?
- Calcium Hydroxyapatite [Ca10(PO4)6(OH)2]
- Trace amounts of calcium carbonate, fluoride,
magnesium and zinc
What organic material is dentin made of?
- 50% of noncollagenous proteins are phosphoprotein
- Sialoprotein and sialophosphoprotein
- Proteoglycans and glycosaminoglycans
- Osteonectin and osteopontin
What collagen does dentin have?
Type I
With trace amounts of type III and V
How is the type I collagen of dentin slightly different than that of bone?
- Higher ratio of proline and hydroxyproline
- Higher prevalence of molecular cross-linking
- Higher level of bound water (Mainly this)
- Random orientation of the hydroxyapatite crystals (also mainly this)
What non-collagenous proteins does dentin include?
Proteoglycans
Glycosaminoglycans
Carboxyglutamate containing protein
Osteonectin
Osteopontin
What are examples of proteoglycans?
Biglycan
Decorin
What are types of glycosaminoglycans?
- Chondroitin-4- sulfate
- Chondroitin-6- sulfate
What are non-collagenous proteins necessary for?
Initiation
They control size of crystals
What does osteopontin contain?
The receptor binding sequence Arginine-Glycine-
Asparagine (Arg-Gly-Asp or a.k.a. the RGD binding complex)
What are the 4 life cycle stages of the odontoblast?
Pre-odontoblast
Secretory Odontoblast
Transitional Odontoblast
Resting Odontoblast
What does the transitional odontoblast stage become?
Autophagic
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 from the IEE
What is the function of pre-odontoblastic fibronectin receeptors?
Allows the cells to align themselves along the basal lamina, assume polarity, and differentiate into secretory cell
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)
What does complete differentiation require?
A set number of cell divisions which allows cells to express appropriate receptors able to bind growth factors localized to the IEE basal lamina
What does last minute division of odontoblast differentiation result in?
a mature odontoblast
and a daughter cell that is forced into the subodontoblastic cell layer
What is the “backup layer” after the pre-odontoblastic layer?
Subodontoblastic layer
What do subodontoblastic layer cells represent?
Ectomesenchymal cells exposed to the entire cascade of developmental controls for odontoblastic differentiation
What cell population is responsible for the reparative odontoblasts that differentiate from pulpal cells?
Cells in the subodontoblastic layer
What cells make up the secretory odontoblast?
Tall columnar cells with extensive junctional complex and gap junction formations
What stage exhibits significant alkaline phosphatase activity?
Secretory odontoblast
What collagen is secreted during the secretory odontoblast stage?
Type I and traces of type III and type V collagen
What matrix vesicles are secreted in the secretory odontoblast stage?
- Alkaline phosphatase
- Ca ++ and PO4-
- Annexin
- Calcium hydroxyapatite crystallites
What does annexin mediate?
flow of Ca++ into the matrix vesicle. Also serves as
a collagen receptor that binds matrix vesicles to collagen
What is mantle dentin?
First formed dentin
What kind of collagen makes up the mantle dentin?
Type I and III collagen
How are collagen fibers in mantle dentin arranged?
Perpendicular to the basal lamina of the IEE
What is mantle dentin secreted by?
Secondary odontoblasts
How is organic matrix of dentin deposited?
Incrementally at a rate of 4 micrometers to 8 mcm per 24 hours
What do incremental lines in dentin (lines of von Ebner) represent?
A hesitation in matrix formation and subsequently altered mineralization that occur after 4-20 days of matrix deposition
What causes incremental lines (e.g., neonatal line, contour lines of owen) or areas of interglobular dentin?
Deficiencies and irregularities in dentinogenesis, resulting in areas of hypomineralization
Where are dentinal tubules tapered to?
- 2.5 µm diameter at the pulpal surface
- 1.2 µm diameter at midlength
- 0.9 µm near the DEJ
Narrower at DEJ, wider at pulpal surface
Where are dentin tubules more and less at?
More at pulp
Less at DEJ
What is peritubular dentin?
Denser, more calcified and resistant than intertubular dentin
Where do cell processes branch?
They anastamose at basement membrane
What is interglobular dentin?
A zone of globular, rather than linear,
formed dentin in the crowns of teeth
What is interglobular dentin characterized by?
interglobular spaces that are unmineralized or hypomineralized
dentin between normal calcified dentinal layers
What is the tome’s granular layer?
A granular-appearing layer in the dentin of the root adjacent to the cementum
What is tome’s granular layer comprised of?
Hypomineralized interglobular dentin
What is primary dentin?
All dentin (except mantle dentin) formed up
to the time the tooth achieves functional occlusion
What is secondary dentin?
All dentin formed (except tertiary dentin)
formed after tooth achieves functional occlusion
What are dead tracts?
Dentinal tubules that are void of the odontoblastic
process
What are dead tracts filled with?
Air or organic debris (or empty) and look black in transmitted light microscopy
What is sclerotic dentin?
Dentin in which the tubules are occluded with mineral
The dentin is non-tubular and is nearly transparent
When does the incidence of sclerotic dentin increase?
With age
May also be tertiary (reparative) dentin
When do lines of Von Ebner occur?
4-20 days of matrix deposition
What do von ebner lines represent?
hesitations in matrix
deposition and therefore altered mineralization
What do neonatal lines and contour lines of owen represent?
Both represent exaggerated lines of von Ebner that occur during periods of altered cell metabolism
Neonatal- caused by trauma from birth. Whatever part of the tooth was forming at the time of birth (considered a traumatic event) will hold and then continue on
Owen- caused by hesitations seen in maturation stages of the dentin
When does tetracycline staining occur?
When taking tetracycline while tooth growth is occurring
What is tertiary dentin (aka reparative dentin)?
Dentin deposited by newly differentiated odontoblasts at the site of pulpal trauma
What is tertiary dentin a defensive reaction for?
To attempt to wall off the pulp from the site of injury (e.g., caries)
What happens when cells in the subodontoblastic layer are exposed to growth factors released by stimulated pulpal cells?
Differentiate and form the matrix of reparative dentin
What are growth factors that are released in the subodontoblastic layer that function as tertiary or reparative dentin?
- Bone Morphogenetic Protein (BMP)
- Insulin-like Growth Factor (IGF)
- Fibroblast Growth Factor (FGF)
- Dentin Matrix Protein (DMP)
What is pulp capping?
Bridge of reparative dentin in root canal
What is 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
What happens in dentinogenesis imperfecta at the dentino-enamel junction?
Tubulin is missing = no support between dentin and enamel
What is attrition?
Loss by wear of surface caused by tooth to tooth
contact during mastication or parafunction
Due to bruxism
How can attrition be identified?
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
What is another thing that dental attrition can be due to?
Bruxism (teeth become sensitive to cold)
What is erosion?
Loss of hard dental tissue by chemical processes
What does erosion look like?
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
Describe patients that have erosion
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 to stabilize hydroxyapatite core and make less susceptible to carries
Bacteria responsible for dental caries include:
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)
Describe the spread of dental carries
enamel -> dentin -> pulp
Enamel:
- 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
DEJ:
- 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
Pulp:
- pulp necrosis can occur due to overwhelming of the pulpal tissue with carious lesion
When do caries spread laterally?
After hitting DEJ because it is softer and more organic
What teeth are most commonly affected by dental sensitivity?
Cuspids and bicuspids
aka canines and premolars
What are stimuli associated with dentinal sensitivity?
- 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
What activates and causes sensitivity?
Free nerve endings
What is the direct innervation theory?
Direct stimulation of nerve endings in dentinal tubules
What is the transduction theory?
Stimulation of odontoblasts that are coupled to nerves
in the pulp
What is 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
What is Charles’ law?
The volume of a gas (or fluid) is directly proportional
to the amount of heat applied at a constant pressure
Describe Charles law as it relates to dentistry
If heat is applied to tooth, the volume of fluid in the tubules increases (stimulates nerve endings)
If cold is applied, the volume of fluid in the tubules decreases (stimulates nerve endings)
