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UKCD Histo Dentin

learning objectives for dentin

QuestionAnswer
Is dentin harder than bone? Yes.
What 3 components are common to CT? Cells (odontoblasts); fibers (Type I collagen); and ground substance (proteoglycans and glycoproteins).
Initially what percentage of dnetin is fibrous collagen? Over 90% What happens to the collagen?
What process in the IDE initiates odontogenesis in the pulp? Pre-ameloblasts of the IDE elongate, organize and secrete into the basal lamina causing cells of the peripheral dental papilla to differentiate into odontoblasts.
What is the first step of IDE process? Odontogenesis
Which cell secretes predentin? Odontoblasts
What is mantle dentin? Dentin containing large collagen fibers in dense array preventing hyper-mineralization - leaving it hypomineralized.
Where is mantle dentin located? Just under the DEJ - the peripheral region of initial dentin layer.
What is circumpulpal dentin? Dentin formed at a distance from the DEJ containing finer collagen fibers and surrounding the pulp cavity.
Does mantle dentin get mineralized as circumpulpal dentin? Why or why not? No, it contains larger collagen fibers allowing less space for HA crystal deposition - making it less heavily mineralized.
How do the two types of dentin differ in location, mineralization, collagen fiber size and dentistry? Circumpulpal dentin - smaller collagen fibers packed closely and interwoven, located at a distance from the DEJ, highly mineralized. Mantle dentin - large collagen fibers perpendicular orientation to DEJ, just under DEJ, less heavily mineralized.
What is a dentinal tubule and what does it contain? A tubular hole in mineralized dentin that contains the long slender single odontoblast process.
What general shape do the tubules exists? The primary curvature of the tubules exhibits a gentle sloping S as the odontoblasts of the crown move from a large surface area to a smaller surface area.
Where do the odontoblasts become stratified? In the crown due to the reducing size of the surface area as the odontoblasts move inward toward the pulp.
What is the shape the pathway of the tubules in the root resemble? Primary curvatures of dentinal tubules in the root lack an s-shaped curvature and are more horizontal.
What is a secondary dentinal tubule curvature? A daily slight deviation in direction exhibited by the odontoblasts as they deposit dentin daily.
At what interval do the secondary curvatures occur? A rhythmic diurnal deposition of a 4 micrometer layer of dentin.
Name two regions where dentinal tubule density is increased and the reason for each? DEJ due to branching of individual odontoblast processes as they reached to touch the overlying pre-ameloblasts. 2. Near the dentin-pulp interface where the stratification of odontoblasts in the crown cause an increased number of tubules per unit area.
What is the clinical implication of tubule density near the pulp? The deeper you drill into dentin the larger the number of odontoblasts you are irritating/killing.
What is the clinical implication of tubule density at the DEJ? Due to the branching of odontoblast processes only a small ratio of odontoblasts are irritated when large numbers of these processes are cut.
What is the clinical implication of tubule orientation in the crown? The odontoblasts being irritated/killed in a cavity prep are located at a lower region of the crown due to the primary curvature of the dentin tubule.
Which dentin, root or crown, exhibits more branching aside from terminal branching? Dentin tubules of crown dentin exhibit relatively unbranched processes (aside from terminal branching) when compared to tubules of root dentin.
What can be said of tubule diameter and density at the DEJ? high density, small diameter
What can be said of tubule diameter and density at the mid tubule? lower density, larger diameter
What can be said of tubule diameter and density at the pulp interface? high density, largest diameter.
What does the term “functional diameter” refer to? The functional diameter is space between the calcified wall of the dentinal tubule and the odontoblast process.
Name one other term used for odontoblast process? Tome’s fiber
Name one other term used for functional diameter? periodontoblastic space.
Circumpulpal dentin can be divided into two regions relative to the dentinal tubule, what are they? Peritubular and intertubular dentin comprise circumpulpal dentin (mantle dentin and predentin are not included).
Is peritubular or intertubular dentin more heavily calcified? Where is it located? Peritubular dentin. It forms a lining around the periphery of the dentinal tubule.
In a decalcified section, which of peritubular or intertubular dentin is lost? Peritubular dentin. It contains no collagen so demineralization completely removes it. Compare this to intertubular dentin which stains pink due to the presence of collagen fibers after the removal of HA crystals.
What is interglobular dentin? Small islands of unmineralized dentin. It is found in the crown and the root although more common in the crown primarily between the outer and middle third of the dentin layer.
Why does interglobular dentin exists? Interglobular dentin represents a failure of globular dentin mineralizing masses to fuse, leaving interstitial hypomineralized regions - interglobular dentin.
What is Tome’s granular layer and where is it located? A granular appearing layer in the distal region of radicular dentin. It is thought to be twisted ends of dentinal tubules and/or uncalcified cores of large collagen fibers characteristic of peripheral root dentin.
How do imbrications lines (of von Ebner) differ from contour lines (of Owen) in dentin? I.L.= represent daily diurnal deposition of dentin (4 micrometer intervals). Contour lines reflect illness or major changes in body metabolism that reflect in less calcified bands less common than imbrication lines and follow the contour of the tooth.
What are the 3 mechanisms proposed to explain dentin sensitivity? Intratubular nerves, Transduction and Hydrodynamics
How does the intratubular nerves theory explain dentin sensitivity? dentin contains nerve endings which respond when stimulated
How does the transduction theory explain dentin sensitivity? odontoblasts serve as receptors coupled to nerves in the pulp.
How does the hydrodynamics theory explain dentin sensivitiy? fluid movement in the dentinal tubules interpreted by free nerve endings
How does primary dentin differ from secondary dentin? Primary dentin is formed prior to completion of the apical foramen, secondary forms after this event. Primary exhibits uniform deposition and tubule distribution, secondary is generally more random and/or less numerous.
How does secondary dentin differ from reactive dentin? Secondary dentin forms normally and slowly following formation of the apical foramen. Reactive dentin forms rapidly and in response to an irritant. Secondary may be regular or irregular in morphology, reactive is always highly irregular in morphology.
What is sclerotic dentin? A plug of peritubular dentin secreted to close off the dentinal tubule.
What causes sclerotic dentin? This represents an effort by chronically irritated odontoblasts, who have withdrawn their processes from the tubules, to escape the irritant.
Which cell type secretes sclerotic dentin? Odontoblasts.
What is a dead tract? Dead tracts are empty dentinal tubules (odontoblast processes withdraw in response to irritation).
How does a dead tract differ from sclerotic dentin? A dead tract is an empty dentinal tubule whereas sclerotic dentin is a region of the dential tubule plugged by hypersecretion of peritubular dentin (which incidentally mineralizes immediately on secretion).
Created by: wiechartm