The periodontium develops from neural crest cells that migrate into the developing dental arches. The dental lamina forms and invaginates into the underlying mesenchyme, forming the tooth bud. The bud develops through the cap and bell stages as the enamel organ and dental papilla form. The dental follicle gives rise to the periodontal ligament, cementum and alveolar bone. Cementoblasts deposit cementum on the root surface. Periodontal ligament fibers develop from the dental follicle and insert into the cementum and bone. The gingiva develops as the tooth erupts, with the reduced enamel epithelium transforming into junctional epithelium and sulcular epithelium.
alveolar bone in health with microscopic features and details about bone formation, resorption also includes bone remodelling and changes after extraction
alveolar bone in health with microscopic features and details about bone formation, resorption also includes bone remodelling and changes after extraction
this is a presentation on B lymphocytes and there role in humoral immune response . Dr Harshavardhan Patwal highlights on antibodies and B cell activation to name a few.
Definitions
History
Development of junctional epithelium
Structure
Dynamic aspects of junctional epithelium
Expression of various molecules and their functions
Permeability
Functions
Role of JE in gingivitis
Role of JE in initiation of pocket formation
Passive Eruption
Effect of Trauma from Occlusion on JE
Junctional Epithelium Adjacent to Oral Implants
Syndromes Affecting JE
Regeneration of junctional epithelium
Conclusion
References
Introduction
A sound knowledge of the anatomy of the periodontium and the surrounding hard and soft structures is essential to determine the scope and possibilities of surgical periodontal procedures and to minimize their risks.
Blood vessels, and nerves located in the vicinity of the periodontal surgical field, are particularly important during various surgical procedures.
Arterial Supply
Common Carotid Artery
Carotid Sinus & Carotid Body
Applied Anatomy of CCA
CAROTID PULSE :
CCA may be compressed against the carotid tubercle of transverse process of C6 vertebra about 4cm above the sternoclavicular joint.
External Carotid Artery
Generally it lies anterior to the Internal Carotid Artery.
It is the chief artery of supply to structures in the front of neck, oral cavity and in the face.
In carotid triangle
Crossed superficially by:
Cervical branch of facial nerve
Hypoglossal nerve
Facial, lingual &superior thyroid vein
Deep to artery lies:
Wall of pharynx
Superior laryngeal nerve
Ascending pharyngeal artery
Above the carotid triangle
ECA lies deep in the substance of parotid gland
Branches
Lingual Artery
Principal artery of tongue.
Arises anteromedially from ECA opposite the tip of greater cornu of hyoid bone.
Divided into three parts by hyoglossus muscle.
Applied anatomy
Sublingual artery injury occurs in premolar & molar region, when sharp instrument or rotating disks slips off a lower molar & injure the floor of mouth.
Sublingual and submental arteries may course anteriorly in close proximity to the lingual plate, and branches of these blood vessels enter accessory foramina along the lingual cortex.
Hofschneider et al (1999)
Inadvertent penetration through the lingual cortical plate into the floor of the mouth while preparing an osteotomy can cause arterial trauma, thereby resulting in development of a sublingual or submandibular hematoma
Flanagan D. et al.2003
Facial Artery
ORIGIN: Arises from the ECA just above the tip of greater cornua of hyoid bone.
COURSE:
Runs upwards in neck as cervical part ;
On face as facial part.
Tortuous course—
In neck allows free movements of pharynx during deglutition,
On face allows free movements of mandible , lips, & cheek during mastication & facial expressions, escapes traction & pressure during movements.
Cervical part :
Cervical part runs upwards on superior constrictor of pharynx deep to the posterior belly of digastric.
It grooves the posterior border of submandibular gland, makes S-bend [2 loops]
1st winding down over submandibular gland &
then up over the base of mandible.
Facial part:
The vessel enters the face by winding around the base of the mandible, and by piercing the deep cervical fascia,at the anteroinferior angle of the masseter muscle, here it can be palpated & is called as anaesthetist’s artery. Using contracted masseter as a landmark, pulse of facia
Periodontitis is a chronic infectious inflammatory disease caused by microbes; however the presence of microbes is not enough for the cause of its complex nature of disease. Inflammation is the prime cause of periodontal disease. It commences with the aggregation of pathogenic microbes that induce the host to stimulate a cascade of inflammatory response reactions which in-turn leads to the destruction of the host tissues itself. There is a complex interplay of innate and adaptive immune responses which fights against the pathogens by direct interaction or by release of certain molecules including cytokines.
Cytokines are cell signalling molecules that aid cell to cell communication in immune responses and stimulate the movement of cells towards sites of inflammation, infection and trauma. Cytokine biology reveals that there are some subsets of cytokines which are pro-inflammatory cytokines which stimulate the inflammatory responses and cause tissue destruction.
A periodontist is expected to have a sound basis of the cytokine profile to understand the pathogenesis of periodontitis and also to discover the new treatment modality of anti-cytokine therapy.
THIS PRESENTATION INCLUDES:
INTRODUCTION
MAIN BLOOD SUPPLY BRANCHES TO PERIODONTIUM
BLOOD SUPPLY TO MAXILLARY TEETH AND PERIODONTIUM
BLOOD SUPPLY TO MANDIBULAR TEETH AND PERIODONTIUM
VENOUS DRAINAGE OF MAXILLARY AND MANDIBULAR TEETH AND PERIODONTIUM
BLOOD SUPPLY TO EACH COMPONENT OF PERIODONTIUM
CLINICAL SIGNIFICANCE OF BLOOD SUPPLYING THE PERIODONTIUM
CLINICAL CORELATIONS WITH GINGIVITIS AND PERIODONTITIS
CONCLUSION
REFERENCES
this is a presentation on B lymphocytes and there role in humoral immune response . Dr Harshavardhan Patwal highlights on antibodies and B cell activation to name a few.
Definitions
History
Development of junctional epithelium
Structure
Dynamic aspects of junctional epithelium
Expression of various molecules and their functions
Permeability
Functions
Role of JE in gingivitis
Role of JE in initiation of pocket formation
Passive Eruption
Effect of Trauma from Occlusion on JE
Junctional Epithelium Adjacent to Oral Implants
Syndromes Affecting JE
Regeneration of junctional epithelium
Conclusion
References
Introduction
A sound knowledge of the anatomy of the periodontium and the surrounding hard and soft structures is essential to determine the scope and possibilities of surgical periodontal procedures and to minimize their risks.
Blood vessels, and nerves located in the vicinity of the periodontal surgical field, are particularly important during various surgical procedures.
Arterial Supply
Common Carotid Artery
Carotid Sinus & Carotid Body
Applied Anatomy of CCA
CAROTID PULSE :
CCA may be compressed against the carotid tubercle of transverse process of C6 vertebra about 4cm above the sternoclavicular joint.
External Carotid Artery
Generally it lies anterior to the Internal Carotid Artery.
It is the chief artery of supply to structures in the front of neck, oral cavity and in the face.
In carotid triangle
Crossed superficially by:
Cervical branch of facial nerve
Hypoglossal nerve
Facial, lingual &superior thyroid vein
Deep to artery lies:
Wall of pharynx
Superior laryngeal nerve
Ascending pharyngeal artery
Above the carotid triangle
ECA lies deep in the substance of parotid gland
Branches
Lingual Artery
Principal artery of tongue.
Arises anteromedially from ECA opposite the tip of greater cornu of hyoid bone.
Divided into three parts by hyoglossus muscle.
Applied anatomy
Sublingual artery injury occurs in premolar & molar region, when sharp instrument or rotating disks slips off a lower molar & injure the floor of mouth.
Sublingual and submental arteries may course anteriorly in close proximity to the lingual plate, and branches of these blood vessels enter accessory foramina along the lingual cortex.
Hofschneider et al (1999)
Inadvertent penetration through the lingual cortical plate into the floor of the mouth while preparing an osteotomy can cause arterial trauma, thereby resulting in development of a sublingual or submandibular hematoma
Flanagan D. et al.2003
Facial Artery
ORIGIN: Arises from the ECA just above the tip of greater cornua of hyoid bone.
COURSE:
Runs upwards in neck as cervical part ;
On face as facial part.
Tortuous course—
In neck allows free movements of pharynx during deglutition,
On face allows free movements of mandible , lips, & cheek during mastication & facial expressions, escapes traction & pressure during movements.
Cervical part :
Cervical part runs upwards on superior constrictor of pharynx deep to the posterior belly of digastric.
It grooves the posterior border of submandibular gland, makes S-bend [2 loops]
1st winding down over submandibular gland &
then up over the base of mandible.
Facial part:
The vessel enters the face by winding around the base of the mandible, and by piercing the deep cervical fascia,at the anteroinferior angle of the masseter muscle, here it can be palpated & is called as anaesthetist’s artery. Using contracted masseter as a landmark, pulse of facia
Periodontitis is a chronic infectious inflammatory disease caused by microbes; however the presence of microbes is not enough for the cause of its complex nature of disease. Inflammation is the prime cause of periodontal disease. It commences with the aggregation of pathogenic microbes that induce the host to stimulate a cascade of inflammatory response reactions which in-turn leads to the destruction of the host tissues itself. There is a complex interplay of innate and adaptive immune responses which fights against the pathogens by direct interaction or by release of certain molecules including cytokines.
Cytokines are cell signalling molecules that aid cell to cell communication in immune responses and stimulate the movement of cells towards sites of inflammation, infection and trauma. Cytokine biology reveals that there are some subsets of cytokines which are pro-inflammatory cytokines which stimulate the inflammatory responses and cause tissue destruction.
A periodontist is expected to have a sound basis of the cytokine profile to understand the pathogenesis of periodontitis and also to discover the new treatment modality of anti-cytokine therapy.
THIS PRESENTATION INCLUDES:
INTRODUCTION
MAIN BLOOD SUPPLY BRANCHES TO PERIODONTIUM
BLOOD SUPPLY TO MAXILLARY TEETH AND PERIODONTIUM
BLOOD SUPPLY TO MANDIBULAR TEETH AND PERIODONTIUM
VENOUS DRAINAGE OF MAXILLARY AND MANDIBULAR TEETH AND PERIODONTIUM
BLOOD SUPPLY TO EACH COMPONENT OF PERIODONTIUM
CLINICAL SIGNIFICANCE OF BLOOD SUPPLYING THE PERIODONTIUM
CLINICAL CORELATIONS WITH GINGIVITIS AND PERIODONTITIS
CONCLUSION
REFERENCES
Indian Dental Academy: will be one of the most relevant and exciting training center with best faculty and flexible training programs for dental professionals who wish to advance in their dental practice,Offers certified courses in Dental implants,Orthodontics,Endodontics,Cosmetic Dentistry, Prosthetic Dentistry, Periodontics and General Dentistry.
The initiation of tooth development begins at 37 days of development
with formation of a continuous horseshoe-band of thickened epithelium
in the location of upper and lower jaws – Primary Epithelial Band
Dental lamina appears as a thickening
of the oral epithelium adjacent to
condensation of ectomesenchyme
20 areas of enlargement or knobs
appear, which will form tooth buds
for the 20 primary teeth
Not all will appear at the same time.
The first to develop are those of the
anterior mandible region
At this early stage the tooth buds
have already determined their crown morphology
Successional lamina: lamina from
which permanent teeth develop
The dental lamina begins to function
at 6th prenatal week and continues to
15th year of birth (3rd molar)
Tooth development is a continuous process, however can be
divided into 3 stages:
1. Bud Stage
2. Cap Stage
3. Bell Stage
4. Hertwigs epithelial root sheath and root formation
The bud stage is represented by the first epithelial incursion into the ectomesenchyme of the jaw.
The epithelial cells show little if any change in shape or function.
The supporting ectomesenchymal cells are packed closely beneath and around the epithelial bud. As the epithelial bud continues to proliferate into the ectomesenchyme, cellular density increases immediately adjacent to the epithelial outgrowth.
This process is classically referred to as a condensation of the ectomesenchyme.
The epithelium of the dental lamina separated from the underlying ectomesenchyme by basement membrane.
Bud stage is characterized by rounded, localized growth of
epithelium surrounded by proliferating mesenchymal cells,which are packed closely beneath and around the epithelial buds
The transition from bud to cap marks the onset of morphologic differences between tooth germs that give rise to different types of teeth.
Differential cellular division in the epithelial bud initiates a change in shape so that now the epithelial outgrowth assumes a more complex outline with a flattened internal portion along which the mesenchymal condensation densifies.
As the tooth bud grows larger, it drags along with it part of the dental lamina; thus from that point on, the developing tooth is tethered to the dental lamina by an extension called the lateral lamina.
At this early stage of tooth development, identifying the formative elements of the tooth and its supporting tissues is already possible.
The epithelial outgrowth, which superficially resembles a cap sitting on a ball of condensed ectomesenchyme , is still referred to widely as the dental organ but actually should be called the enamel organ, because it eventually will form the enamel of the tooth. Henceforth, the term enamel organ is used.
Condensation of the ectomesenchyme immediately subjacent to the tooth bud caused by lack of extracellular matrix secretion by the cells thus preventing separation.
The early development of tooth from six week of prenatal life. Description of different stages- bud,cap and bell stage and amelogenesis, dentinogenesis. Description of root development.
Indian Dental Academy: will be one of the most relevant and exciting training center with best faculty and flexible training programs for dental professionals who wish to advance in their dental practice,Offers certified courses in Dental implants,Orthodontics,Endodontics,Cosmetic Dentistry, Prosthetic Dentistry, Periodontics and General Dentistry.
BE UPDATE TO IT,, AS IT IS 3 years back from 2017
Kindly mail me if you feel, needy of this presentation
you can find my mail id @ slide share,,, if not mail me @
sukesh3567@gmail.com.
Good luck
For first year dental student, i got this from the internet.. Hope this can help u guys understand more about the tooth development.. Btw, good luck for minitest OB tomorrow.. No sacrifice, no victory!
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Letter from the Congress of the United States regarding Anti-Semitism sent June 3rd to MIT President Sally Kornbluth, MIT Corp Chair, Mark Gorenberg
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The US House of Representatives is deeply concerned by ongoing and pervasive acts of antisemitic
harassment and intimidation at the Massachusetts Institute of Technology (MIT). Failing to act decisively to ensure a safe learning environment for all students would be a grave dereliction of your responsibilities as President of MIT and Chair of the MIT Corporation.
This Congress will not stand idly by and allow an environment hostile to Jewish students to persist. The House believes that your institution is in violation of Title VI of the Civil Rights Act, and the inability or
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• The Committee on Education and the Workforce has been investigating your institution since December 7, 2023. The Committee has broad jurisdiction over postsecondary education, including its compliance with Title VI of the Civil Rights Act, campus safety concerns over disruptions to the learning environment, and the awarding of federal student aid under the Higher Education Act.
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Overview on Edible Vaccine: Pros & Cons with Mechanism
Development of periodontium
1. DEVELOPMENT OF PERIODONTIUM
“You never know where you are going unless you know where you came from”
DR. T.MADHAVI
PERIO PG
The periodontium is defined as those tissues supporting & investing the tooth,
comprising of
1. Cementum
2. Periodontal ligament
3. Bone lining the alveolus (socket)
4. That part of the gingiva facing the tooth
Following the development of the neural tube, the neural crest cells (NCC) migrate
from the dorsal midline region of the neural tube to invade the developing branchial
arches. Dye injected tracings have shown that neural crest cells from the posterior
midbrain, and to a lesser extent from the anterior hindbrain, form dental
ectomesenchyme. Subsets of cranial neural crest cells give rise to chondrocytes,
osteoblasts, periodontal ligament fibroblasts, cementoblasts and odontoblasts.
The failure of the normal migration of neural crest ectomesenchymal cells to
appropriate sites during craniofacial development leads to serious developmental
defects.
Dental lamina
Two or three weeks after the rupture of the buccopharyngeal membrane, when the
embryo is 6 weeks old, certain areas of basal cells of the oral ectoderm proliferate
2. more rapidly. This leads to formation of the dental lamina. It is a band of epithelium
that has invaded the underlying ectomesenchyme along each of the horseshoe- shaped
future dental arches. The dental laminae serve as the primordium for the ectodermal
portion of the deciduous teeth.
Tooth Development
The developmental history of a tooth is divided into several morphogenetic “stages”.
They are named after the shape of the epithelial part of the tooth germ and are called
Bud stage
Cap stage
Bell stage
Bud stage: Portions of epithelium in dental lamina, first begin to aggregate and
invaginate into underlying connective tissue
Cap stage: the enamel organ is in its earliest stage of development. The dental papilla
and dental follicle are formed by concentration of neural crest ectomesenchyme cells.
The interaction b/w cell surface syndecan and tenascin (extra cellular matrix adhesion
molecule) reduces migration and promotes aggregation of the ectomesenchymal cells
to form papilla & follicle.
3. Immediately underneath the epithelial cap, mesenchymal cells begin to proliferate and
form dental papilla. These cells further proliferate and encapsulate the enamel organ
to form dental sac.
(The syndecans: In the early 1990s a group of scientists discovered that a number of
components of the extra-cellular microenvironment had a high affinity for binding
with heparin. These extra-cellular components included growth factor peptides,
proteases, antiproteases and ECM molecules which, by binding to a cell, could
produce changes in cell shape, motility, adhesion, proliferation and differentiation.
They discovered that there is a family of integral membrane proteoglycans made up of
heparan and chondroitin sulphate, both structural analogues of heparin, which can
also bind to a wide variety of structural proteins and growth factors in the internal
and external cellular environment. They named these molecules the syndecans, from
the Greek ‘syndein’ which means ‘to bind together’. It has since been shown that by
binding to extra-cellular ligands, syndecans can mediate the activity of the ligands
and enable the cells to become more or less responsive to their microenvironment.
They are also involved in the maintenance of cell morphology. For example, if
syndecans are not expressed in epithelial cells, then the cells become rounded in
shape.
At present, four members of this family have been identified.
Syndecan-1, the most prevalent of the group, is expressed predominantly in epithelial
tissues.
Syndecan-2 predominates in tissues rich in endothelial cells.
4. Syndecan-3 is found primarily in neural tissues.
Syndecan-4 mainly in the liver and kidney.)
Bell Stage: enamel organ continues to enlarge and takes on a bell shaped appearance.
Four different types of cells can be distinguished on light microscopic examination.
Inner enamel epithelium – it consists of a single layer of cells that differentiate into
tall columnar ameloblasts. The cells of IEE exert an organizing influence on the
underlying mesenchymal cells in the dental papilla, which later differentiate into
odontoblasts.
Outer enamel epithelium – the cells are low cuboidal. During the formation of enamel,
the OEE is laid in folds. Between the folds, the adjacent mesenchyme of the dental sac
forms papillae that contain capillary loops and thus provide a rich nutritional supply
for the avascular enamel organ.
Stratum intermedium – a few layers of squamous cells between IEE and stellate
reticulum. Essential for enamel formation.
Stellate reticulum – the cells are star shaped with long processes and intercellular
fluid. The layer collapses before enamel formation to reduce the distance between
ameloblasts and the nutrient capillaries near OEE.
Advanced bell stage: formation of future DEJ – the boundary between the IEE and the
odontoblasts – membrana preformativa. The cervical loop of enamel organ gives rise
to HERS.
5. Development of periodontium
Mesenchyme deriving periodontium has two compartments:
1. Alveolar clade: fibroblasts, osteoblasts
2. Cement clade: fibroblasts, cementoblasts
Dental follicle (dental sac) gives rise to cementum, periodontal ligament and the
alveolar bone.
Dental follicle anatomically consists of dental follicle proper, perifollicular
mesenchyme.
6. Dental follicle proper: well defined band of cells juxtaposed to the dental papilla and
the convex outer surface
CEMENTUM
The cementum is a specialized mineralized tissue covering the root surfaces. After
enamel & dentin formation has reached the future CEJ, enamel organ forms the
Hertwig’s epithelial root sheath (HERS). HERS consists of the outer and inner enamel
epithelia. The structural continuity of HERS is lost once there is differentiation of
radicular cells into odontoblasts & first layer of root dentin is laid. The remnants of
HERS persist as cell rests of Malassez which are found in the periodontal ligament of
erupted teeth.
The intact epithelial sheath is located between the dental papilla and the dental follicle
proper. Cells of the dental follicle proper project cytoplasmic processes from their
leading edge towards and into the intercellular space between the root sheath cells.
These cells are identified as precementoblasts. The unidirectional migration of
precementoblasts towards the predentin surface appears to contribute to the breakup of
the root sheath and the formation of Sharpey’s fibres. Upon contact with the predentin
surface, the elongated precementoblasts become cuboidal in shape and differentiate
into cementoblasts.
Following a brief period of cementogenesis, the cementoblasts appear to detach from
the newly formed cementum surface and join the fibroblast population in the
periodontal ligament.
Primary cementum formation
Once differentiated, the cementoblasts deposit collagen fibrils at right angles to the
root surface so that the root has a series of fine collagen fibrils attached to it. The
7. cementoblasts then migrate away but continue to deposit collagen so that the fine fiber
bundles not only lengthen to maintain a fibrous fringe on the root surface, but also
thicken to form the fibrous matrix of acellular cementum. Cementoblasts also secrete
non collagenous proteins such as bone sialoprotein and osteocalcin.
This first formed cementum is acellular, as the cells that form it remain on its surface;
develops relatively slowly as the tooth is erupting; and covers atleast the coronal two
thirds of the root. First formed cementum thus consists of a mineralized layer with a
fibrous fringe attached to it. This continues until the forming periodontal ligament
fiber bundles become attached to the fibrous fringe. No surface layer of unmineralized
matrix is associated with acellular cementum.
Secondary cementum formation
Once the tooth is in occlusion, a more rapidly formed and less mineralized form of
cementum is deposited around the apical third of the root. Cementoblasts become
trapped in the matrix they are forming to occupy lacunae, and the cells become
cementocytes.
Five major types of cementum – Schroeder 1992
1. Acellular intrinsic fiber cementum
2. Acellular extrinsic fiber cementum
3. Cellular intrinsic fiber cementum
4. Cellular mixed fiber cementum
5. Acellular afibrillar cementum
8. Acellular intrinsic fiber cementum
First formed cementum as a result of cementoblastic activity and is elaborated before
the periodontal ligament forms, therefore the collagen is intrinsic. During
cementogenesis, osteopontin is prominent in intrinsic fiber cementum.
Acellular extrinsic fiber cementum
Once the PDL fiber bundles are formed and get connected to fibrous fringe bundles of
the acellular intrinsic fiber cementum, further deposition of mineral about and within
the bundles results in the formation of acellular extrinsic fiber cementum. It is made
up of a particular class of fibroblasts that are alkaline phosphatase positive.
Cellular intrinsic fiber cementum
The cells forming this cementum resemble the bone-forming cells. When first
deposited, the periodontal ligament is unorganized, the cementoblasts deposit the
organic matrix directly onto the root surface. No evidence of insertion of the sharpey’s
fibers. It is commonly associated with the healing of root fractures and repair of
resorptive defects.
Cellular mixed fiber cementum
It consists of intrinsic collagen fibers produced by the cementoblasts and some
extrinsic sharpey’s fibers.
Acellular afibrillar cementum
It is limited to the enamel surface and appears as cemental spurs or cemental islands
on the crowns of erupted teeth. It represents aberration where, a part of REE
disaggregates and the cells of dental follicle interact with the exposed enamel matrix,
leading to cementum deposition.
9. PERIODONTAL LIGAMENT
The development of periodontal ligament begins with root formation prior to tooth
eruption.
The mesenchymal cells of perifollicular region attain polarity, increased cellular
volume and synthetic activity. They become elongated. There is an increase in RER,
mitochondria and active golgi complex which synthesize collagen fibrils and
glycoprotein.
Principal fibers
The development of the major collagen bundles, the principle fibers of the periodontal
ligament, is closely related to root formation.
Fiber bundles originate at the surface of the newly formed root dentin in close relation
to elongated and highly polarized fibroblasts. The fringe fibers are tightly packed by
the action of cementoblasts. As the periodontal ligament matures, the fringe fibers
merge across the width of the ligament to form the principle fiber bundles. During the
development of the fringe fibers, fibroblasts exhibit cytoplasmic polarity towards the
root and alveolar bone surfaces. A specific cementum attachment protein favours the
PDL fibroblast attachment to the cementum surface.
10. With continued development of the root, the principle fibres are established as
continuous structures embedded as Sharpey’s fibers in bone and cementum.
The figure illustrating the development of principle fibres of periodontal ligament.
Bone Cementum
m
1. First, small, fine, brush- like fibrils --- root cementum
projecting into periodontal ligament space. From the
surface of the bone: small number of radiating, thin
collagen fibrils project into the periodontal ligament
space.
2 & 3. The number and thickness of the fibers entering the
bone increase. The fibers entering the bone are also longer
while those entering the cementum are still short.
4. The fibers entering the cementum increase in length and
thickness and fuse with fibres originating from the alveolar
bone in the periodontal ligament space.
(intermediate zone)
Bone Cementum
m
11. Oxytalan fibers: These are demonstrated in connective tissues destined to become
PDL when about 2mm of dentin is formed in the developing root.
They increase in size and rearrange themselves with further root development
Cells: The cells of the periodontal ligament are fibroblasts, osteoblasts, cementoblasts,
cementoclasts, and epithelial cells.
Viable cells are required for tooth movement.
1. Fibroblasts: These are the principle cells and most abundant cells in the
periodontal ligament and metabolize the extra cellular matrix components.
Fibroblasts help in remodelling: both synthesize & degrade collagen.
Subpopulation of osteoblast- like fibroblasts: these form bone cells &
cementoblasts, and are rich in alkaline phosphatase. They help in the
production of Acellular extrinsic fiber cementum.
2. Epithelial cells: Remnants of HERS, close to the cemental surface. These are
the Rests of Malassez.
3. The developing periodontal ligament consists of undifferentiated mesenchymal
cells or progenitor cells that retain the ability to differentiate into osteoblasts,
cementoblasts and fibroblasts.
4. Bone and cementum cells: Although technically situated in the PDL, bone and
cementum cells are properly associated with the hard tissues they form.
Development of neurovascular elements
In the early bell stage: rich innervation associated with small blood vessels is found in
the inner investing layer of dental follicle. As the root formation continues and the
tooth erupts, nerves grow into periodontal ligament. Vasculature is derived from the
networks associated with enamel organ & alveolar mucosa, vessels spread apically to
supply PDL.
12. GINGIVA
It is that part of the oral mucosa that covers the alveolar process of the jaws and
surrounds the necks of the teeth.
It comprises gingival epithelial and connective tissue. The epithelial component shows
regional morphological variations that include oral gingival epithelium, oral sulcular
epithelium and junctional epithelium.
The gingiva evolves as the crown enters the oral cavity by breaking through the oral
epithelium.
Development
The crown of the tooth is covered by a double layer of epithelial cells at the time it
begins its eruptive movements.
1. Those cells in contact with the enamel are the ameloblasts, which, having
completed their formative function, become firmly attached to the enamel
surface.
2. The outer layer consists of more flattened cells, the remnants of all the
remaining layers of the dental organ.
The above two layers of cells, together are called the reduced enamel epithelium.
Between the REE and the overlying oral epithelium is connective tissue that supports
both the REE and the oral epithelium.
When tooth eruption begins, this connective tissue breaks down. In response to the
degenerative changes occurring in the connective tissue, the cells of the outer layer of
the reduced enamel epithelium and the basal cells of the oral epithelium proliferate
and migrate into the degenerating connective tissue and eventually fuse to establish a
mass of epithelial cells over the erupting tooth. Cell death at the middle of this
RE
E
13. epithelial plug leads to the formation of an epithelium- lined canal through which the
tooth erupts without hemorrhage.
From this mass of epithelium, the epithelial cuff, together with the remaining REE, the
epithelial component of the dentogingival junction is established. Once the tip of the
cusp of the erupting tooth emerges into the oral cavity, oral epithelial cells begin to
migrate partially over the REE in an apical direction. The attachment of the gingival
epithelium to tooth is maintained through the reduced ameloblasts and their hemi
desmosomes and basal lamina adjacent to the enamel surface. This is the primary
epithelial attachment.
The REE transforms gradually to become Junctional epithelium. The reduced
ameloblasts change their morphology and are transformed into squamous epithelial
cells that retain their attachment to the enamel surface. The cells of the outer layer of
the REE retain their ability to divide continuously to become and function as basal
cells of the forming Junctional epithelium. The transformed ameloblasts are
eventually displaced by the mitotic activity of these basal cells.
Meanwhile, the cells of the epithelial cuff stratify separating the cells of transformed
dental epithelium from the nutritive supply, resulting in the degenerating of latter cells
creating a gingival sulcus. The final conversion of the REE to JE may not occur until
3- 4 years after the tooth has erupted. Thus the epithelial component of the
dentogingival junction is formed, the JE from REE and the sulcular epithelium from
epithelial cuff. The JE derived from dental epithelium is eventually replaced by JE
formed from oral epithelial cells.
Development of gingival connective tissue
Gingival connective tissue fibroblasts originate from perifollicular mesenchyme.
During normal development, gingival fibroblasts do not come into contact with the
tooth surface. Gingival collagen turns over more rapidly than that of skin and bone,
but slower than that of periodontal ligament. The collagen matrix of gingival
connective tissue is well organized into fiber bundles.
14. ALVEOLAR BONE
Alveolar bone proper
• Late bell stage: bony septa, bony bridges- clearly outlined bony compartments
around tooth germs.
• Bony compartments + tooth germ: bodily movements to adjust to growing jaws
– minor bone remodeling
• Major changes: root development & eruption
• Cells of dental follicle– osteoblasts – alveolar bone proper
• Size and shape of individual tooth roots determine overall structure
• Insertion of sharpey’s fibers
• Rest of the bony structures: periosteal bone formation
Remodeling
• At root formation: Alveolar process is over the occlusal plane of tooth.
• Tooth eruption: remodeling
• Gubernacular canal
• New bone at base of bony crypt
15. EPITHELIAL MESENCHYMAL TISSUE INTERACTIONS
General features
Tissue morphology and phenotype are controlled by a complex interplay between
tissues of ectodermal and mesodermal origin. The interactions are controlled through
secreted products released from cells residing within both of these tissues and are
regulated via the genetic code of these cells.
Spemann (1938) demonstrated that for organogenesis to proceed, some form of
communication between the epithelial and mesenchymal tissues was required. This
interaction was called secondary embryonic induction and was shown to regulate
morphogenesis and cell differentiation.
The following are some examples that provide useful insight into the development of
teeth.
1. If epithelium from a developing tooth bud site is placed onto mesenchyme
distant from the dental arch, no tooth formation results.
2. If epithelium from a site that normally does not produce teeth is layered over
mesenchyme from the dental arch, then normal tooth bud formation occurs.
3. If epithelium from a developing tooth bud site is placed over the connective
tissue derived from the neural crest, then tooth development progresses.
These findings indicate that in undifferentiated tissues (such as neural crest cells)
the epithelium has an instructive component leading to the development of the
ectomesenchyme. Once this differentiation process has been initiated, the
ectomesenchyme adopts the dominant role in epithelial- mesenchymal interactions.
16. Once the enamel organ has formed during tooth development, the cells of the inner
enamel epithelium induce the adjacent cells in the dental papilla to differentiate
into odontoblasts: epithelium influencing mesenchyme.
Genetic features
The pathway of initiation, morphogenesis, and differentiation involves the production
of molecular signals via the initiation of gene expression.
Genetic codes for signaling mechanisms—instruct cells leading to organ development
E.g. transcription factors: these are nuclear proteins that bind to DNA and control the
expression of other genes.
Homeobox (Hox) genes: specify spatial location of future tooth germs.
Dlx-1 & 2 is noted in areas of epithelial thickening.
Molecular features
Following gene expression, locally secreted molecules control cell differentiation &
organ development.
Growth factors, cell surface glycoproteins, components of extracellular matrix appear
to be prime candidates for governing developmental processes. These exert their
influence on cells via specific cell surface receptors
During odontogenesis, BMPs, TGF- ß, FGF (fibroblast growth factor) have been
found to be differentially expressed according to the stage of development,
morphogenesis and cell differentiation.
Other growth factors including PDGF, EGF and growth hormone have been
associated with different stages of tooth development.
TGF- ß1 is first seen in the epithelial thickenings that dictate sites of developing teeth.
Shortly after this it is expressed in the underlying mesenchyme.
17. BMP-2, BMP-4 -- Budding epithelium....Mesenchyme.
FGF-3
FGF-4
Extracellular matrix
Components of extracellular matrix and cell surface--- instructional effect on cells
18. Initiated from mesenchymal cells---- influence ectodermal tissues
Tenascin : condensing mesenchyme of dental papilla
Tenascin, fibronectin --- bell stage --- odontoblast differentiation.
Syndecan – 1 --- early bud stage through cap stage --- condensing mesenchyme of
dental papilla
Decreases during transition from cap to bell
EGF – high in epithelium in bud stage, shifts to mesenchyme in bell stage.
Summary
The development of periodontal tissues involves both ectodermal and mesenchymal
tissues.
A good understanding of the principles of formation of periodontal structures is
essential for unraveling the mechanisms associated with tissue regeneration.
The clinical ramifications lie in the regulatory mechanisms governing the correct
expression of epithelial & connective tissue components during regeneration and r.
repair.