Oral Bio II Midterm part 2.txt
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what stage does most of the dev of supporting tissues take place? what is the tissue of origin?
Most development of the supporting tissues takes place in the late bell stage of development; All supporting tissues are derived from the ectomesenchyme of the dental follicle (= dental sac). This surrounds the developing enamel organ and is continuous with but external to the dental papilla.
Dental Follicle - list the structures it forms:
- the dental follicle develops into the supporting structures of the tooth including:
- Periodontal ligament.
- Cementum covering the root of the tooth.
- Supporting bone – the alveolus.
- That part of THE LAMINA PROPRIA OF THE GINGIVA FACING THE TOOTH.
Describe the lamina propria:
The lamina propria is the connective tissue of a mucosa (moist epithelium) that attaches tooth to socket?
When does Root Formation begin?
Once the formation of the crown is complete, root formation begins.
At the cervical loop the enamel organ has only 2 layers:
- Inner enamel epithelium.
- Outer enamel epithelium.
Describe origin of Hertwig’s Epithelial Root Sheath (HERS).
From the two layers IEE and OEE at the cervical loop, an epithelial structure known as Hertwig’s Epithelia Root Sheath (HERS) originates and continues to grow apically.
What role does HERS play in tooth dev.?
HERS induces peripheral cells in the dental papilla to differentiate into odontoblasts that will then secrete the dentin of the root.
As soon as root dentin has started to form at a cervical region, HERS at that region does what? why?
HERS fragments, so that at any one time HERS is only seen as a thin band of cells around the most apical portion of the growing root. The fragmentation of HERS allows cells from the dental follicle to come into contact with the newly formed dentin and secrete a protective layer of cementum over the outer surface of the developing root.
Describe the Apical Foramen Development.
- At the apical portion of the developing root, HERS also forms an epithelial diaphragm.
- This epithelial diaphragm is an inward projection of HERS that induces the differentiation of dental papilla cells in that region and will determine the size of the future apical foramen.
function of Epithelial Diaphragm?
While HERS is growing apically, the epithelial diaphragm is growing inwards to decrease the size of the future apical foramen. The manner in which this inward growth occurs determines the number of roots that will be formed.
describe how blood vessels and epithelial diaphragm interact to determine root formation:
The number and location of the individual groups of blood vessels determines how many roots will be formed. There is an area around each group of blood vessels that prevents the epithelial diaphragm from contacting that group of vessels.
Define and describe Accessory Canals:
If there are blood vessels that enter the dental papilla from areas other than apically, HERS will induce dentin formation around these vessels. This results in access to the pulp not only via the apical foramen but also via these additional channels also known as “accessory canals”.
What are Epithelial Rests of Malassez? why are they clinically significant?
When HERS fragments it leaves remnants of epithelial that appear as small clusters of cells known as the epithelial rests of Malassez. The epithelial rests of Malassez remain in the periodontal ligament throughout the life of the tooth. They are clinical significant in that they have the potential to develop into cysts.
Tooth Development Theories: what are the two General development theories? what are the two "theories for location of specific tooth types?"
- Tooth General Development: Classical Theory and Functional Theory
- Theories of Locations for Specific Tooth Development: Field Theory and Clonal Theory
Functional Theory of Tooth Development, name the Three stages of physical & biochemical cell changes:
- 1. Initiation stage-(lamina plus bud stages of the classical theory)
- 2. Proliferation and condensation stage – involves some proliferation and organization of cells. (Cap plus early bell stages of the classical theory)
- 3. Morphogenesis and cytodifferentiation stage – when the individual tissue morphology can be seen. (late bell stage of the classical theory).
The determination of different tooth types in specific locations is commonly known as: ? name the two theories explaining it.
dentition patterning; The Two theories are currently used to explain this patterning:
Describe the "Field Theory"
Type of tooth that develops depends on the specific microenvironment of the ectomesenchyme. Supported by the expression of various homeobox genes in specific and overlapping patterns. This, as with tooth initiation, involves epithelial-mesenchymal interactions.
Describe the Clonal Theory.
This theory states that the ectomesenchymal cells that migrate from the neural crest are made up of three clones and that each of these clones is programmed by the epithelium to produce a specific tooth type.
Describe the possible overlap of the Field and Clonal theories.
It is most probable that a combination of the factors involved in each theory is responsible for tooth type.
Oral ectoderm gives rise to:
- Primary epithelial band.
- Dental lamina (and successional lamina).
- Enamel organ and all its layers.
- HERS and epithelial diaphragm.
- Epithelial rests of Malassez.
- Reduced enamel organ and its derivatives.
Ectomesenchyme gives rise to:
- Dental pulp and all its cells.
- Dental follicle (dental sac).
- Supporting bone (alveolus).
- Periodontal ligament and all its cells.
- Cementoblasts and cementum.
- Lamina propria of the gingiva facing tooth.
T/F: Enamel formation once completed ceases - fully mineralized enamel can be biologically repaired.
False, it cannot be biologically repaired once completed.
T/F Dentin formation continues throughout the life of a vital tooth.
failure of teeth to develop.
Define Hypodontia –
fewer numbers of teeth than normal develop.
Define Hyperdontia –
greater number of teeth than normal develop.
Define Dens in dente –
tooth within a tooth.
Define Gemination –
twinning of teeth.
where are Dentin and pulp usually described together?
because the odontoblasts have: Cell bodies in pulp and Processes in ECM of dentin
Describe Dental pulp:
Dental pulp Appears as pink-red gelatinous material. it contains loose areolar fibrous connective tissue; it is composed of cells and ECM, it develops from dental papilla and is of ectomesenchymal origin (neural crest origin)
Unique characteristics of pulp:
- Continuous production of dentin
- Enclosed within a non-yielding chamber of dentin
- Requires protection against occulusal wearing and invasion of antigens
Cells in Pulp:
- Undifferentiated mesenchymal cells
- T-lymphocytes and other immune cells
- and dendritic antigen presenting cells
Describe Dendritic antigen presenting cells:
Similar in function to langerhan’s cells (periphery of pulp)These have processes that may pass btw odontoblasts to enter some dentinal tubules
ECM contains what fibers and ground substance?
- Fibers – Collagen type I, III (most are type I) with larger collagen bundles in the center of the pulp
- Ground substance – GAG; Glycoproteins; Water
Pulp regions are divided into what regions? what does each contain?
- central and peripheral regions, but No sharp distinction btw two regions
- The Central pulp region contains moost major blood vessels trunks and nerves trunks and
- Thick collagen bundles.
- The Peripheral region contains Peripheral nerves and blood vessels and Odontoblasts – single layer; cell free zone; cell rich zone; plexus of raschkow; dendritic antigen presenting cells
describe Cell free zone
few nuclei but processes are present. it is adjacent to the odontoblast layer
What is the Plexus of Raschkow
Plexus of nerve endings - close proximity to basal ends of odontoblasts
Name and describe Peripheral Regions (in order)
- Odontoblasts: a Single layer at periphery of pulp
- Plexus of Raschkow - a plexus of nerve endings in close proximity to the basal ends of the odontoblasts
- Cell free zone - adjacent to the odontoblasts layer. has relatively few nuclei but does contain cell processes.
- Cell rich zone - numerous cell nuclei
describe odontoblast part of peripheral region
A single layer of cells at the periphery of the pulp that: contain junctional complexes btw adjacent odontoblasts; are in Close association with nerves-Both individual nerves and also with the plexus of raschkow in the subodontoblastic layer
The odontoblast stages/ Morphology changes according to their functional state as –
- Secretory – very active
- Transitional – somewhat active
- Resting – relatively inactive
differentiate types of Odontoblasts (3) and their shape/location:
- 1. Coronal odontoblasts – are Tall columnar and very active
- 2. Root canal odontoblasts – Low columnar/cuboidal and Less active
- 3. Apical foramen odontoblasts – (root apex) Low cuboidal/squamous- Very low active
describe Secretory odontoblasts:
- their Nucleus located near base of the cell
- have Large amounts of RER and Golgi
- possess Junctional complexes with adjacent odontoblasts
- in Close association with nerves in pulp
Describe pulp vessels and nerves:
- Major blood vessel trunks and nerve trunks are in the central region of pulp with branches are distributed to the peripheral pulp.
- With multi rooted teeth, there is overlap btw the blood vessels from each root canal
Elaborate on Pulp vasculature (functional considerations)
- Rich vascular in enclosed/unyielding chamber
- -Vessels entering pulp are arterioles (often described as pulpal arteries)
- -Large vessels are in central pulp
- -Unique anastomoses near apical foramen that prevent excessive pressure buildup in the pulp when systemic pressure increases
Describe Lymphatics in the pulp:
- -Blind ended vessels identical to those in other tissues
- -Distinguished from capillaries by the absence of red blood cells and presence of occasional lymphocytes
Describe Nerves in the pulp:
- -A-delta (myelinated) - sense Sharp localized pain
- -C-fibers (non-myelinated) – sense Dull diffuse pain
- -Plexus of raschkow – is a Subodontoblastic plexus of nerves
what can cause Calcifications in pulp?
Usually as a result of degenerating/apoptotic cells or tissues acting as focal points for mineral salts: Ex: some collagen bundles that are not metabolized as rapidly by less active fibroblasts can become brittle and can act as areas for mineralization
name the two Types of calcifications in pulp:
- -Diffuse Calcifications: Mineralization around debris that often assumes the same shape of the tissue that is being mineralized (if distinct shape it's called pulp stone)
- -Pulp stones (denticles): Mineral deposition that often occurs as concentric layers, increase with time; Denticles may be free in pulp or may be attached to the dentin
Distinguish between true denticles and false denticles, and how to distinguish:
- True denticles if formed by odontoblasts
- False denticles if formed by an accumulation of mineral around debris often in a concentric manner
- -Cannot distinguish btw true or false denticles unless dentinal tubules are visible in the pulp stone
Dentinogenesis begins with what steps?
- Cells of the inner enamel epithelium differentiate into PREAMELOBLASTS
- Preameloblasts and stratum intermedium complex induce undifferentiated mesenchymal cells in the periphery of developing dental pulp to differentiate into preodontoblasts
when does dentinogenesis begin?
dentin synthesis starts at the LATE BELL STAGE
what occurs after Preodontoblasts are formed? describe preodontoblasts.
- PO's are tall columnar cells that develop all the organelles necessary to synthesize dentin matrix
- -As soon as any dentin matrix is synthesized, preodontoblasts are called odontoblasts
Dentinogenesis of the crown begins where? and progresses in what direction?
Dentin formation of crown – starts at the cusps, progresses apically ending at the cervix of the tooth
describe the general process of dentin formation:
- -Odontoblasts first secrete an extracellular non-mineralized matrix – PREDENTIN
- -Odontoblasts move away from the DEJ but have a process that becomes surrounded by this matrix; the process resides in the dentinal tubule
- -Matrix then becomes mineralized
Dentin forms at the rate of
4 microns/day (same rate as enamel)
what is the last region on the future crown that the dentin is formed?
Starts at the cusps and progresses apically past region on the future crown for odontoblasts to differentiate and lay down dentin of the crown – CERVIX (future neck) of the tooth
describe Mantle Dentin and its formation:
When the initial dentin is formed at the DEJ, odontoblasts are separated from each other, and the region between already contains pulpal ECM; The Odontoblasts synthesize their own ECM into an ECM already present; this Combination of ECMs forms a dentin – MANTLE DENTIN
following creation of mantle dentin, what occurs?
- -As more matrix is secreted, odontoblasts become closer together and soon contact adjacent odontoblasts
- -Junctional complexes form and make a solid sheet of cells
- (Dentin from this point on is composed of ECM secreted only by the odontoblasts)
what type of dentin is closest to the DEJ and CDJ?
Mantle dentin is closes to the DEJ and CDJ
What are VON KORFF’S FIBERS?
It is mantle dentin: (early investigators) stained silver and fibers between adjacent odontoblasts in the initial dentin; Electron microscope showed these are not fibers but differences in the ECM composition
where and when does dentin of root begin formation?
Once the crown dentin has been formed, dentin of the root will start to form beginning at the cervical loop (composed of inner and outer enamel epithelial cell layers) where you find HERTWIG’S EPITHELIAL ROOT SHEATH (HERS) - formed at the cervical loop
describe role of HERS and - the process of Root Formation
HERS induces undifferentiated mesenchymal cells in the developing pulp to differentiate into preodontoblasts Once these start to produce dentin matrix they are known as odontoblasts. As soon as some dentin has been formed at that area, HERS fragments allowing Cells from the dental follicle differentiate into cementoblasts and penetrate through the spaces in HERS and secrete a layer of cementum on the external surface of the newly formed dentin.
T/F: There is, at any one point in time, only a small band of HERS present - at the leading edge in which dentin is yet to be formed.
describe the Epithelial Rests of Malassez.
Formation of the Apical ForamenThe fragments of HERS that remain in the PDL can be seen as clusters of epithelial cells known as the
what is the name for the inward growth of the leading edge of HERS at the apical end of root formation?
the Epithelial diaphragm - it helps to determine the size of the apical foramen and the number of roots.
describe the Formation of Apical Foramen
The number of groups of blood vessels entering the developing pulp determines the number of roots that will be formed. The epithelial diaphragm grows inwards between the groups of blood vessels but is restricted from coming too close to the blood vessels.EXAMPLE: For a tooth with two roots there will be two groups of blood vessels with HERS growing downwards for each root.
How are Accessory Canals formed?
Sometimes blood vessels enter the pulp from regions other apically. - As HERS will grow around vessels, extra canals are formed and are known as accessory canals. These are clinically significant especially during endodontic procedures.
Some Things you should know
- o What is the main function of the pulp?
- o What forms the root of the tooth?
- o What causes false denticles to form?
- o What is the most common fiber in the dental pulp?
- o Von Korff’s fibers are located where?
describe the Pattern of Dentin Mineralization and role of calcospheres:
- Mineralization starts at several small separate points in the predentin.
- Growth of minerals at these points results in the formation of spherical structures known as calcospherites. Calcospherites increase in size until they fuse with adjacent calcospherites to fully mineralize the predentin in this region. The mineralization front between dentin and predentin is therefore often irregular.
What is globular dentin? where are they commonly found?
Failure of the calcospherites to completely fuse results in non-mineralized areas of dentin known as globular dentin (=interglobular dentin). These are most commonly seen in the dentin of the crown.
What are contour lines of Owen?
Even small changes in the degree of mineralization results in the formation of a layer of dentin with a slightly different composition. This dentin appears as darker lines known as the contour lines of Owen. Contour lines of Owen indicate the layer of dentin of the identical composition formed by those odontoblasts synthesizing dentin at the same time. Lines may be thin or broad depending on the length of the time period during which this dentin of different composition was formed.
this Forms the bulk of the tooth.
Crown dentin is covered with (1), while Root dentin is covered with (2).
T/F Dentin exposed to surrounding connective tissue will become reabsorbed.
False, Dentin exposed to surrounding connective tissue will become resorbed.
List the Components of Dentin
- Odontoblasts – with their processes in dentinal tubules in predentin and dentin.
Components of Dentin: Describe the Extracellular matrix by weight:
- 70% inorganic.
- 20% organic.
- 10% water.
components of Dentin: Name the Inorganic Components of ECM:
Hydroxyapatite - Ca10(PO4)6(OH)2
components of Dentin: name the Organic Components of ECM:
- Primarily collagen type I
- Non collagenous proteins: Dentin sialoprotein. Dentin phosphoproteins. Osteocalcin; Osteonectin; Osteopontin; Organic Components
what are the functions of the Non collagenous proteins:
May perform a variety of functions including adhesion of bone cells, coordinating activity of bone cells, aiding in mineraliztion.
how far do dentinal tubules reach in the dentin?
- Dentinal tubules extend from the pulp ALMOST to the DEJ and DCJ.
- Small channels exist between adjacent odontoblasts.
describe peritubular dentin:
Dentin around the periphery of each tubule is of higher inorganic content and is known as peritubular (= intratubular) dentin.
describe inter tubular dentin:
Dentin between tubules is known as intertubular dentin.
Describe Tomes Granular layer:
The tubule for each odontoblast branches close to the DCJ and is known as Tomes Granular Layer. (because odontoblasts start to develop with several processes that then merge as one process). This granular appearance is chiefly confined to the root of the tooth and therefore the DCJ. Tomes granular layer is the first area of the root to be damaged during any operative procedures. Tomes granular layer can only be seen when using ground sections of teeth when air or stain is trapped in these ends of the dentinal tubules.
Name the Types of Dentin
- o Mantle dentin.
- o Physiologic primary dentin.
- o Physiologic secondary dentin.
- o Tertiary dentin.
- o Globular dentin
Describe Mantle Dentin
This is the dentin formed closest to the DEJ and DCJ. its Composition is different than the rest of the dentin due to the different extracellular matrix composition and the presence of von Korff’s fibers.
T/F Mantle dentin is included in primary physiologic dentin.
Describe Primary Physiologic Dentin
- Dentin that is formed until the external shape of the tooth is complete.
- NOTE: primary dentin is not complete when the crown is completed forming or when the tooth erupts but is when the external shape of the entire tooth is complete.
Describe Secondary Physiologic Dentin:
The dentin that is formed after primary dentin formation is complete. Secondary dentin is formed for the life of the tooth - as long as the pulp is vital with functional odontoblasts.
Describe Tertiary Dentin:
Dentin formed in response to a noxious stimulus such as caries and functions to seal the pulp from the stimulus. Tertiary dentin has fewer dentinal tubules than physiologic dentin and in some cases no tubules.
Name the types of Tertiary Dentin, and describe each
- Depending on the odontoblasts synthesizing it as either:
- 1. Reactionary Dentin: Dentin formed by odontoblast that has survived the noxious stimulus.
- 2. Reparative Dentin: The original odontoblasts have undergone apoptosis and a new group of odontoblasts have differentiated from undifferentiated mesenchymal cells in the dental pulp. Many clinical texts use the term reparative dentin to include all tertiary dentin.
discuss identification of tertiary dentin and types using modern microscopy:
It is possible to identify tertiary dentin especially when caries can be seen and when dead tracts are present. However, it is not possible currently on a histologic and histochemical level, to distinguish between reactionary and reparative dentin.
What are Dead tracts?
Dentinal tubules that become exposed and filled with air. Dead tracts allow access to the dental pulp.
what is Sclerotic dentin?
Dentinal tubules that have become filled with dentin secreted by the odontoblasts. This process progresses from the periphery towards the pulp and increases with age.
Briefly describe the Nerves of Dentin and corresponding Sensitivity:
- A-delta myelinated: Sharp, localized pain.
- C-fibers non-myelinated: Dull, diffuse pain
- Plexus of Raschkow: A sub-odontoblastic plexus of nerves
What are the three Theories of Dentin Sensitivity?
1. direct innervation; 2. odontoblasts as receptors (transduction theory); 3. Hydrodynamic Theory
what is the evidence supporting Direct Innervation theory?
Nerve fibers can be seen entering some dentinal tubules. More nerve fibers are found in tubules in the coronal than the root region and the coronal region is generally more sensitive.
describe evidence of Odontoblasts as Receptors theory:
Odontoblasts are in direct contact with nerve fibers. Odontoblasts are close to the nerve plexus of Raschkow.
What is the evidence for Hydrodynamic Theory (Most widely accepted theory).
Pain is felt when the integrity of tubules in damaged. Pain is felt when air is blown over cut ends. Root dentin sensitivity occurs when the granular layer of Tomes damaged.
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