Anatomy and Histology of the Periodontium

Question 1

What is the periodontum made up of?

Answer 1

Cementum
PDL
Alveolar bone
Gingiva

Question 2

What is the cementum?

Answer 2

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

Question 3

What are the characteristics of the cementum?

Answer 3

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

Question 4

What are the classification of the cementum?

Answer 4

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

Question 5

How do the PDL and the cementum interact?

Answer 5

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

Question 6

What is the PDL?

Answer 6

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

Question 7

What are the functions of the PDL?

Answer 7

Provision of the tissue attachment between the tooth and alveolar bone. Thus is responsible of tooth support and protection
Responsibility for the mechanism by which the tooth attains and maintains its functional position
Maintenance and repair of cementum and alveolar bone Neurological control of mastication by its mechanoreceptors

Question 8

What is the composition of the PDL?

Answer 8

Fibres: collagen, oxytalan
Ground substance
Cells: fibroblasts, cementoblasts,osteoblasts, osteoclasts, cementoclasts, epithelial cells

Question 9

What type of collagen is present in the PDL?

Answer 9

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 architecture regulation
Much of the collagen is gathered into bundles (the principal fibres) 5μm in diameter

Question 10

What are the fibres called in the PDL

Answer 10

Principal fibres

Question 11

Name the 5 different orientation of the principle fibres?

Answer 11

1. Dentoalveolar crest fibres 2. Horizontal fibres.

3. Oblique fibres 4. Apical fibres 5. Interradicular fibres

Question 12

What is the zone of shear?

Answer 12

Site of remodelling during eruption

Question 13

What are the Sharpey’s fibres?

Answer 13

The collagen fibres inserted into cementum and bone

Question 14

What is Oxytalan?

Answer 14

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

Question 15

What is the composition of ground substance?

Answer 15

Mainly secreted by fibroblasts: Hyaluronate glycosaminoglycans
Proteoglycans: Proteodermatan sulphate
PG1 (contains hybrids of chondroitin sulphate and dermatan sulphate)
Glycoproteins
Fibronectin
Tenascin

Question 16

Name the cells of the PDL?

Answer 16

1. Fibroblasts 2. Cementoblasts. 3. Osteoblasts 4. Osteoclasts and cementoclasts.5. Epithelial cells 6. Immune cells

Question 17

What are fibroblasts and their functions?

Answer 17

Responsible for the regeneration of the periodontal ligament
Role in adaptive responses to mechanical loading
Shape variations
Many cytoplasmic processes
Low nuclear/cytoplasmic ratio
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

Question 18

What are cementoblasts?

Answer 18

They line the surface of the cementum

Question 19

What are osteoblasts and their functions?

Answer 19

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.

Question 20

What are osteoclasts and their function?

Answer 20

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

Question 21

How are epithelial cells involved in the periodontium?

Answer 21

Epithelial cell rests of Malassez
Closely packed cuboidal cells
Basal lamina
Cyst formation when stimulated

Question 22

How is the PDL supplied with blood?

Answer 22

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

Question 23

How is the PDL supplied with nerve supply?

Answer 23

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

Question 24

What is the alveolar bone and its function?

Answer 24

The part of the jaw that supports and protects the teeth

Question 25

What is the composition of bone?

Answer 25

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

Question 26

Describe the organic matrix of the bone?

Answer 26

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 osteoprogenitor cells.

Question 27

What are the different types of bone cells and their functions?

Answer 27

Osteoblasts secrete the organic extracellular matrix of new bone Osteoid which rapidly undergoes mineralisation to form bone.
Osteoblasts become trapped in bone in lacunae 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.

Question 28

What are the 2 main forms of bone and their structure?

Answer 28

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)

Question 29

What is the composition/structure of compact bone?

Answer 29

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)

Question 30

What is the composition/structure of the spongy bone?

Answer 30

Cancellous (spongy) bone is made of a network of bone trabeculae separated by interconnected spaces containing bone marrow.
Trabeculae are thin and composed of irregular bone lamellae
No haversian canals are present in cancellous bone and osteocytes 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
Trabeculae are aligned along lines of stress so as to withstand forces applied to the bone while adding minimally to the mass

Question 31

What is the name of the landmark which shows bone resorption?

Answer 31

Bone resorption: Howship’s lacunae.

Longer snail track resorption lacunae

Question 32

What is resting bone?

Answer 32

projections marking the sites of extrinsic mineralised Sharpey’s fibres
Separated by areas with intrinsic mineralised collagen

Question 33

What is the structure of the alveolar bone?

Answer 33

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

Question 34

When does bone remodelling occur?

Answer 34

During childhood, bone deposition exceeds resorption

Question 35

How does bone remodelling occur?

Answer 35

Bone resorption factors affect mainly osteoblasts: Osteoblasts could stimulate the production of osteoclasts by their 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

Question 36

What are the sharpey’s fibres?

Answer 36

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

Question 37

What is the gingiva

Answer 37

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

Question 38

What are the characteristics of of the gingiva

Answer 38

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

Question 39

What is the free gingiva?

Answer 39

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

Question 40

What is the sulcular epithelium?

Answer 40

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

Question 41

What is the junctional epithelium?

Answer 41

Junctional epitheliumextends from CEJ to the sulcus base.
2mm.
Thinner apically.
5-6 days turnover rate

Question 42

What is the crevicular fluid?

Answer 42

The gingival crevicular fluid is the fluid within the sulcus.
Results from the permeability of the junctional epithelium.
Important in the defence mechanism

Question 43

What is the interdental papilla?

Answer 43

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

Question 44

What is the col?

Answer 44

The epithelium of the col is continuous with the junctional epithelium.
Spaced teeth have no col

Question 45

What is the gingival lamina propria?

Answer 45

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

Question 46

What are the names of the fibrs present in the gingival lamina propria?

Answer 46

Dentoginigval fibres
Longitudinal fibres
Circular fibres
Alveologingival fibres
Dentoperiosteal fibres
Transseptal fibres
Semicircular fibres
Transgingival fibres
Interdental fibres
Vertical fibres

Question 47

What are cementicles?

Answer 47

Excess growth of the cementum which enters the PDL, or reduces the amount of attached gingiva