Anatomy and Histology of the periodontium Flashcards
What is the periodontum made up of?
Cementum
PDL
Alveolar bone
Gingiva
What is the cementum?
Thin layer of calcified tissue covering radicular dentine • Cervically, it is 10-15µm in thickness • Apically, it is 50-200µm thick • Could exceed 600µm at root apex • Adheres to dentine and to the periodontal ligament
What are the characteristics of the cementum?
Capable of repair and regeneration.
• Formed throughout life, allowing reattachment of the periodontal ligament.
• Similar to bone in composition, but not
innervated and avascular.
• Cementum is pale yellow and has a dull surface.
• Easily abraded cervically
What are the classification of the cementum?
Cellular and Acellular
Cellular cementum contains cementocytes.
• Acellular cementum covers the dentine.
• Cellular cementum mainly in the apical area and
inter-radicular areas overlying acellular cementum
How do the PDL and the cementum interact?
Fibres in the periodontal ligament run into the organic matrix of the precementum • Mineralisation of the precementum leads to the incorporation of these fibres • They are known as Sharpey’s fibres
What is the PDL?
Dense fibrous connective tissue that occupies the space between the root and the alveolar bone • Continuous with the gingival connective tissue and the pulp • Variation in width; location, function and age • Narrower in permanent teeth
What are the functions of the PDL?
Provision of the tissue attachment between
the tooth and alveolar bone. Thus is responsible of tooth support and protection
2. Responsibility for the mechanism by which
the tooth attains and maintains its functional
position
3. Maintenance and repair of cementum and
alveolar bone
4. Neurological control of mastication by its
mechanoreceptors
What are the components of the PDL?
Fibres: collagen, oxytalan 2. Ground substance 3. Cells: fibroblasts, cementoblasts, osteoblasts, osteoclasts, cementoclasts, epithelial cells
What type of collagen is present in the PDL?
70% type I, 20% type III.
• Small amounts of types V and VI
• Traces of IV and VII with the rests of malassez
and blood vessels
• Type XII collagen: non fibrous, , linked to other
collagens and may be involved in the
periodontal ligament’s architecture regulation
• Much of the collagen is gathered into bundles
(the principal fibres) 5μm in diameter
What are the fibres called in the PDL
Principal fibres
Name the 5 different orientation of the principle fibres?
1. Dentoalveolar crest fibres. 2. Horizontal fibres. 3. Oblique fibres. 4. Apical fibres. 5. Interradicular fibres
What is the zone of shear?
Site of remodelling during
eruption
What are the Sharpey’s fibres?
The collagen fibres
inserted into cementum and bone
What is Oxytalan?
Oxytalan fibrils are
unbanded arranged
parallel to the long axis of
the fibre.
Immature elastin fibres (pre-elastin) • 3% of fibre composition • Attached to cementum and leave to the ligament in different directions • Rarely incorporated in bone • Different course according to region • Terminate around blood vessels and nerves • Fibres are 0.5μm-2.5μm in diameter
What is the composition of ground substance?
Mainly secreted by fibroblasts: • Hyaluronate glycosaminoglycans • Proteoglycans: • Proteodermatan sulphate • PG1 (contains hybrids of chondroitin sulphate and dermatan sulphate) • Glycoproteins • Fibronectin • Tenascin
Name the cells of the PDL?
- Fibroblasts
- Cementoblasts.
- Osteoblasts
- Osteoclasts and cementoclasts.
- Epithelial cells
- Immune cells
What are fibroblasts and their functions?
Responsible for the regeneration of the periodontal ligament • Role in adaptive responses to mechanical loading • Shape variations • Many cytoplasmic processes • Low nuclear/cytoplasmic ration • Prominent nucleoli • Protein synthesizing organelles
Collagen degradation (fibroblasts are also fibroclastic) • Intracellular collagen profiles • Secretion of matrix metalloproteinases and tissue inhibitors to metalloproteinases • Collagenase production is regulated by exposure of cytokines
What are cementoblasts?
They line the surface of the cementum
What are osteoblasts and their functions?
They line the tooth socket. • Resemble cementoblasts. • Prominent when there is active bone formation. • Basophilic cytoplasm, cuboidal cells. • Prominent basal round nucleus, protein synthesizing organelles. • Inactive osteoblasts are flat. • Desmosomes and tight junctions. • Fine cytoplasmic processes.
What are osteoclasts and their function?
Cementoclasts = odontoclasts
• They arise from blood macrophages
• Howship’s lacunae in bone.
• Small mononuclear to giant multinuclear
• Brush border: striated part of the cell that is
adjacent to bone, they represent microvilli
• Many vesicles with acid phosphatase
How are epithelial cells involved in the periodontium?
Epithelial cell rests of Malassez • Closely packed cuboidal cells • Basal lamina • Cyst formation when stimulated
How is the PDL supplied with blood?
Superior and inferior alveolar arteries • Arteries perforating the alveolar bone • Arteries entering the pulp • Major vessels between principal fibres • Capillary plexus around teeth • Fenestrations • Veins do not accompany the arteries • Intra-alveolar venous networks, prominent around the apex of the alveolus
How is the PDL supplied with nerve supply?
Sensory nerve fibres: nociception and
mechanoreception
• Autonomic nerve fibres: blood vessels
• Nerve fibres enter via the apical region of the
ligament, while others enter through the alveolar wall
What is the alveolar bone and its function?
The part of the jaw
that supports and
protects the teeth
What is the composition of bone?
Bone is composed of 60% inorganic component, 25%
organic component and 15% water by weight.
Inorganic composition:
Calcium hydroxyapatite Ca10(PO4)6(OH)2. Mainly
carbonated hydroxyapatite in the form of needle-like
crystallites or thin plates.
Organic composition:
Collagen (mainly type I) forms 90% of the extracellular
matrix. There are also serum proteins, acidic
glycoproteins and small proteoglycans
Describe the organic matrix of the bone?
Over 90% of the organic matrix is made of collagen fibrils, mainly
collagen type I.
• Proteoglycans such as chondroitin sulphate and heparan sulphate
glycosaminoglycans mainly in the form of decorin and biglycan.
• Proteoglycans may regulate collagen fibril diameters and may
have a role in mineralisation.
• Glycoproteins such as osteonectin, osteopontin, thrombospondin,
osteocalcin and fibronectin are also present.
• Osteonectin can bind to calcium and thus is thought to be
involved in mineralisation.
Osteocalcin is only synthesised by osteoblasts and odontoblasts.
• Exogenous proteins that circulate the blood and become locked in
bone such as cytokines and growth factors have an important role
in the life cycle of bone cells.
• Bone morphogenetic proteins (BMP)s are present in bone. There
are 8 proteins in this family (BMP-1 to BMP-8). They are part of the
transforming growth factor beta (TGF-β) family (apart from BMP-1).
• BMP(s) induce bone formation by influencing the movement, cell
division, and differentiation of stem and osteoproginator cells.
What are the different types of bone cells and their functions?
• Osteoblasts secrete the organic extracellular
matrix of new bone Osteoid which rapidly
undergoes mineralisation to form bone.
• Osteoblasts become trapped in bone in lacunae
as osteocytes.
• Osteoclasts are multinuclear cells involved in
bone remodelling.
• Bone lining cells: flat cells line bone during
periods of inactivity.
• Osteoprogenitor cells: Stem cells beneath the
osteoblast layer.
What are the 2 main forms of bone and their structure?
Woven bone is immature bone, with random
organisation of its collagen.
Lamellar bone is composed of successive
layers (lamellae). It may be formed as a solid
mass (compact bone), or in an open sponge-like
manner (cancellous bone)
What is the composition/structure of compact bone?
Compact bone is made of parallel bone columns which are disposed parallel to the long axis of long bones (in line of stress exerted on the bone) • Columns are made of concentric bony layers (lamellae) arranged around a central channel with blood vessels, lymphatics and nerves (Haversian canals)
Haversian canals with their lamella form the
haversian systems (osteon).
• Neurovascular bundles interact with each
other via Volkmann’s canals that pierce the
columns at right angle or obliquely to haversian
canals.
• Osteocytes in their lacunae interact with each
other and with the central canal via cytoplasmic
extensions in canals called canaliculi.
• The outermost layer of compact bone gives
way to dense cortical bone
Because of its position, compact bone acts as weight
bearing pillars.
• Compact bone is able to withstand high levels of
mechanical stress.
• The innermost aspect of compact bone, the lamellae
merge with trabeculae of cancellous (spongy bone)
What is the composition/structure of the spongy bone?
Cancellous (spongy) bone is made of a network of bone trabiculae separated by interconnected spaces containing bone marrow. • Trabiculae are thin and composed of irregular bone lamellae
No haversian canals are present in
cancellous bone and oscteocytes get their
nutrition via canaliculi connecting them to blood
sinusoids in the marrow
• Spongy bone gives bone its flexibility due to
the presence of marrow spaces
• Trabiculae are aligned along lines of stress
so as to withstand forces applied to the bone
while adding minimally to the mass
What is the name of the landmark which shows bone resorption?
Bone resorption: Howship’s lacunae.
• Longer snail track resorption lacunae
What is resting bone?
projections marking the sites of extrinsic mineralised Sharpey’s fibres Separated by areas with intrinsic mineralised collagen
What is the structure of the alveolar bone?
• Outer and inner parallel alveolar plates • Sockets are separated by interdental septa • Roots are separated by interradicular septa • Fundus: socket floor • Cribriform plate, bundle bone • In radiographs, thin white line, the lamina dura
Cribriform plate 0.1- 0.5mm in thickness • External alveolar plates 1.5-3mm in thickness • Variable around anterior teeth
When does bone remodelling occur?
During childhood, bone
deposition exceeds
resorption
How does bone remodelling occur?
Bone resorption factors affect mainly osteoblasts: • Osteoblasts could stimulate the production of osteoclasts by the release of cytokines and growth factors. • Osteoblasts could produce enzymes that degrade osteoid thus exposing bone for osteoclasts to work on
Reversal lines marks the change in bone activity. • Constant remodelling to adapt to pressure
What are the sharpey’s fibres?
Extrinsic fibres.
• They enter the bone perpendicular to the surface.
• Less numerous but thicker than those in
cementum.
• Two main appearances under SEM (anorganic):
• Fibres remain unmineralised at their centres,
resulting in hollow centres.
• Fully mineralised project beyond bone surface
as small calcified prominences
What is the gingiva
The portion of the oral mucosa that surrounds
and is attached to the teeth.
• Two main regions:
• The attached gingiva
Directly bound to the underlying bone and
tooth
• The free gingiva
Narrow, not bound to any bone
• The free gingival groove demarcates the free
from the attached gingiva (40% of teeth)
The gingival margin is the coronal limit of the free gingiva • The gingival sulcus is the unattached region between the free gingiva and the tooth • The junctional epithelium is the area where the gingiva is bound to the tooth
What are the characteristics of of the gingiva
The free gingival groove follows the contour
of the cemento-enamel junction.
• Principal fibres running from cementum to
the gingiva.
• Heavy epithelial ridges.
• Healthy gingiva shows stippling,
corresponding to epithelial ridges
What is the free gingiva?
The free gingival mucosa is identical to the attached gingiva.
• The gingival sulcus is 0.5-2.0mm deep in healthy gingiva.
• Sulci deeper than 3.0mm are considered periodontal pockets
What is the sulcular epithelium?
Sulcular and junctional epithelia form the
ginigval cuff.
• Sulcular epithelium has a more folded interface
with the lamina propria.
• Sulcular epithelium is thin.
• The base of the sulcus is at the same level as
the free gingival groove
What is the junctional epithelium?
Junctional epithelium extends from CEJ to the sulcus base. • 2mm. • Thinner apically. •5-6 days turnover rate
What is the crevicular fluid?
The gingival crevicular fluid is the fluid within
the sulcus.
• Results from the permeability of the junctional
epithelium.
• Important in the defence mechanism
What is the interdental papilla?
The interdental gingiva occupies the area
between adjacent teeth.
• Its shape and size depend on the shape and
contact between teeth.
• Wedge shaped appearance on the buccal and
lingual sides.
• Pointed between anterior teeth.
• The interdental col a curved depression across
the buccolingual plane.
• It fills the contour around the contact point
What is the col?
The epithelium of the col is continuous with the junctional epithelium. •Spaced teeth have no col
What is the gingival lamina propria/
Dense collagen bundles:
• Support the free gingiva.
• Bind the attached gingiva to the alveolar
bone and the tooth.
• Linkage of teeth to each other.
• Principal fibres divided into groups according
to their location
What are the names of the fibrs present in the gingival lamina propria?
- Dentoginigval fibres
- Longitudinal fibres
- Circular fibres
- Alveologingival fibres
- Dentoperiosteal fibres
- Transseptal fibres
- Semicircular fibres
- Transgingival fibres
- Interdental fibres
- Vertical fibres
What are cementicles?
Excess growth of the cementum which enters the PDL, or reduces the amount of attached gingiva
