The Anatomy & Physiology of the Periodontium

Question 1

What are the 4 components of the Peridontium?

Answer 1

Cementum
Periodontal Ligament
Alveolar Bone
Gingiva

Question 2

What are the type types of Histological sectioning that you will encounter?

Answer 2

Ground Sectioning
Decalcification
Cryomicrotomy

Question 3

What is Ground section? give an example of a useful application to the process and a negative aspect.

Answer 3

Ground sectioning is used on non-decalicifed teeth. Useful for observing the hard tissue (enamel, dentin and cementum).

The teeth are literally ground down with a diamond saw/abrasive material.

The downside is that soft tissue is disrupted and can not be analysed.

Question 4

What is decalcification? give an example of a useful application and a negative aspect.

Answer 4

Decalcification is the process of removing mineral from calcified tissue so that good quality paraffin sections can be prepared. It allows for the observation of soft tooth tissue such as the pulp and connective tissue.

Unfortunately you cannot see any of the calcified material (enamel etc).

Question 5

What does the Periodontium do?

Answer 5

It supports the tooth in the jaw

Question 6

Whats the cementum?

Answer 6

A pale yellow calcified tissue providing protective covering for the root surface to which the periodontal ligament fibres are secured.

Question 7

What does the cementum adhere to?

Answer 7

It adheres to the roots dentine by a glue-like substance known as the hyaline layer.

It adheres to the periodontal ligament fibres. The embedded ends of the periodontal collagen fibres are called Sharpey’s fibres and are histologically different to the other collagen fibres.

Question 8

How does the thinkness of the cementum vary along the tooth?

Answer 8

Cervically (the neck between the crown and root) it is only 10-15μm thick.

As you move apically (towards the apex) it is 50-200μm thick.

At the root apex it can be 600μm thick.

Question 9

What is the risk to Cementum if a patient has gingivitis/periodontitis?

Answer 9

Apical migration of the attached gingiva can expose the cementum cervically causing it to be abrasively removed when brushing.

Question 10

What are the two main types of Cementum?

Answer 10

Acellular (Primary) & Cellular (Secondary)

Question 11

Whats the composition of Cementum?

Answer 11

65% inorganic hydroxyapatite, 23% organic collagen and 12% water

Question 12

Does the Cementum have nerves?

Answer 12

No

Question 13

What are the type types of Cementum?

Answer 13

Acellular (Primary) & Cellular (Secondary)

Question 14

What are the main differences between Cementum subtypes and whats the significance of them both?

Answer 14

When the cementum 1st forms from the dental follicle it is acellular and covers the dental dentine.

Cellular cementum has a similar structure to bone with cementocytes embedded in a lacunae (small cavity) which have cytoplasmic processes linking each other via canaliculi (channels).

Question 15

Is Cementum formation continuous throughout adulthood?

Answer 15

Yes. Cementum formation (cementogenesis) continues throughout life and is dependent upon the functional needs of the tooth and any tooth movement which may occur.

Question 16

Can resorption of the cementum occur?

Answer 16

Yes. Resorption occurs in response to excessive occlusal stress or orthodontic loading.

Question 17

Where is cellular cementum normally located?

Answer 17

It is located mainly in the apical area and intra-radicular areas of overlying acellular cementum.

It often covers apical 2/3 of the roots.

Question 18

How is the Cementum attached to the Periodontal Ligament?

Answer 18

Collagen fibres in the periodontal ligament run into the organic matrix of the precementum. This precementum is unmineralised and thin; can also be called cementoid on Acellular extrinsic fibre cementum (AEFC).

When the precementum becomes mineralised it leads to the fibres being incorporated. Once this happens they are known as Sharpey’s fibres.

Question 19

The is the Periodontal Ligament?

Answer 19

The periodontal ligament is a dense connection tissue layer enveloping the roots of teeth; occupying the space between the root (and cementum) and alveolar bone.

Question 20

What are the 4 key functions of periodontal ligaments?

Answer 20

1. Provision of the tissue attachment between the tooth and alveolar bone. This is responsible for tooth support and protection.
2. Responsible for the mechanism by which the tooth attains and maintains its function position.
3. Maintenance and repair of the cementum and alveolar bone.
4. Neurological control of mastication by its mechanoreceptors.

Question 21

What is the Periodontal ligament composed of?

Answer 21

1. Fibres: Collagen (desmodontium) & Oxytalan
2. Ground Substance
3. Cells: Fibroblasts, cementoblasts, osteoblasts, osteoclasts, cementoclasts, epithelial cells

Question 22

Which type of collagen is the most abundant in periodontal ligaments?

Answer 22

70% of the collagen is type I fibrils & 20% is type II. There are traces of IV and VII with the rests of malassez and blood vessels.

Question 23

What are the Rests of Malassez and what are their relevance to the periodontium?

Answer 23

Their origin is with the Hertwig’s root sheath. This is a layer of epithelial cells formed from the downward growth of the inner and outer enamel epithelium of the developing tooth germ.

The Hertwig’s root sheat maps out the shape of the root. It atrophies once the root is formed and any residual cells are known as the rest cells of Malassez. They are found near the cementum of most teeth, around the apical and cervical area.

Believe that it might:

• maintain periodontal ligament homeostasis to prevent ankylosis (fusion of cementum or dentin to the alveolar bone)
• potentially harbour epithelial stem-cell populations that have similar properties to mmesenchymal stromal/stem cells (aid periodontal regeneration)

Question 24

How is a large proportion of collagen arranged?

Answer 24

It is gathered into bundles known are the PRINCIPLE FIBRES; these are around 5μm in diameter.

Question 25

What are Principle fibres?

Answer 25

Bundles of collagen fibrils. They are more numerous but smaller at their attachment with Cementum in comparison to alveolar bone. They unravel into smaller fibres which join up with those of adjacent fibres to produce a meshwork of interconnected fibres oriented between bone and cementum.

Question 26

A principle fibre is made of?

Answer 26

Collagen fibril subunits. 3 fibrils are wound together to make a collagen fibre.

Question 27

Principle fibres (Dentoalveolar fibre group) have multiple orientations, what are they?

Answer 27

1. Dentoaveolar crest fibres (fibres from the roots to alveolar bone proper 2. Horizontal fibres ( Mid-root to adjacent alveolar bone proper) 3. Oblique fibres (apical one thrid of root to adjacent alveolar bone proper) 4. Apical fibres (apex of the root to alveolar bone proper) 5. Interradicular fibres (vertical inbetween the roots)

Question 28

The Gingival fibre group has multiple orientations, what are they?

Answer 28

1. Dentogingival fibres: Insert into the supracrestal root cementum and fan out into the adjacent connective tissue. 2. Dentoperiosteal fibres: insert into the supracrestal root cementum and blend with the periosteal covering of the adjacent alveolar process. 3. Alveologingival fibres: insert into the alveolar crest ad fan out into the adjacent gingival connective tissue. 4. Circumferential fibres: Follow a circular course around individual dental units. 5. Semicircular fibres insert into the approximal surfaces of a tooth and follow a semicircular course to insert on the opposite side of the same tooth. 6. Transgingival fibres: insert into the approximal surface of a tooth and fan out towards the oral or vestibular surface. 7. Intergingival fibres: course along the oral or vestibular surfaces of the dental arch 8. Transseptal fibres: course from one approximal tooth surface to the approximal surface of the adjacent tooth

Question 29

What is Col?

Answer 29

A valley like depression which connects the gingival papillae situated in the interproximal space between the two teeth. It lies below, and conforms to the shape of the interproximal contact between teeth.

Question 30

Do tooth related and bone related collagen fibres meet?

Answer 30

They intercalate in an intermediate pluxus in the middle (plexus = a network)

Question 31

Is collagen more numerous at the cemental or bone attachment?

Answer 31

Cemental

Question 32

Is there a fast turnover of collagen in the Periodontal ligament?

Answer 32

Yes

Question 33

Whats Oxytalan?

Answer 33

Oxytalan is immature elastin fibres (pre-elastin) which are bound to the cementum and leave parallel and oblique to the root surface. Their function is to maintain the patency (open/unobstructed) of blood vessels during occlusal loading.

Question 34

What is ground Substance?

Answer 34

It is a complex biochemical matrix which is secreted by fibroblasts which surround the collagen fibres, oxytalan and the other cells of the periodontal ligament.

Question 35

What is the composition of the ground substance?

Answer 35

Hyaluronate glycosaminoglycans, Proteoglycans (Proteodermatan sulphate & PG1), Glycoproteins (Fibronectin & Tenascin)

Question 36

What cells are present in the Periodontal Ligament?

Answer 36

1. Fibroblasts 2. Cementoblasts 3. Osteoblasts 4. Osteoclasts & Cementoclasts 5. Epithelial cells 6. Immune cells

Question 37

What are the roles and features of Fibroblasts?

Answer 37

1. They are responsible for the regeneration of the peridontal ligament and aid in adaptive responses to mechanical loading. 1b. They degrade collagen (collagenase) (technically they are fibroclastic) 1c. Secretion of matrix metalloproteinases (degrade matrix in periodontitis) 2. They have many cytoplasmic processes indicating they are very active, they have a low nuclear/cytoplasmic ratio (small nucleus, indicates mature cells) & they are protein synthesizing organelles

Question 38

What are the role and feature of Cementoblasts?

Answer 38

They line the surface of the cementum. Their function is cementogenesis which is the formation of new cementum. They resemble osteoclasts but differ functionally and histologically. When they become trapped in the cementum they are known as Cementocytes.

Question 39

What are the roles and features of Osteoblasts?

Answer 39

Osteoblasts line the tooth socket and resemble Cementoblasts. They are prominent when there is active bone formation as they secrete: collagen and specialised proteins such as osteocalcin and osteopontin. Furthermore they produce hydroylapatite

Question 40

Whats the relation between Epithelial cells in and cysts?

Answer 40

Epithelial cell stimulated in the Rest of Malassez causes cellular proliferation/division. the centre of the growing masses is void of oxygen so the cells die. Changes in water concentration and an increasing mass causes a cyst to form.

Question 41

What the roles and features of immune cells?

Answer 41

There are 3 prominent immune cells in the Periodontal ligament: 1. Macrophages: 4% of cell population and are derivates of monocytes and phagocytosis. They are attacking organisms which increase the immune response in the area. 2. Mast Cells: These cells degranulate when stimulated. Secreting histamine, heparin and anaphylactic factors. Causes inflammation, blood thinning and edema. 3. Eosinophils: White blood cell associated with allergies

Question 42

Detail some features of the Blood Supply to the Periodontal Ligament.

Answer 42

There is the superior and inferior alveolar arteries and these are perforating the alveolar bone. Major vessels are intertwined between the principle fibres with a capillary plexus around the teeth.

Question 43

Is there a nerve supply in the periodontal ligament?

Answer 43

There are sensory nerve fibres with both nociception and mechanoreception. They detect pain and mechanical load.

Question 44

What is Alveolar bone?

Answer 44

Alveolar bone is part of the jaw that supports and protects teeth.

Question 45

What is the composition of the Alveolar bone?

Answer 45

The bone is composed of 60% inorganic material (calcium hydroxyapatite and mainly carbonated hydroxyapatite in the form of needle like crystallites or thin plates. 25% organic material. Type I Collagen forms 90% of the extracellular matrix, there are also some proteoglycans (may regulate collagen fbril diameter and mineralisation) and glycoproteins (osteonectin which canbind calcium; making it involved in mineralisation + synthesised by osteoblasts). 15% is water

Question 46

What are the bone cells?

Answer 46

Osteoblasts: secrete organic extracellular matrix of now bone osteoid which undergoes rapid mineralisation to form bone. When they become trapped they are known as Osteocytes. Osteoclasts: Multinuclear cells involved in bone remodelling Osteoprogenitor cells: Stem cells beneath the osteoblast layer.

Question 47

What are the two main forms of bone? forms of bone

Answer 47

Woven: Immature bone with random organisation of its collagen Lamellar: Composed of successive layers (Lamellae). It can either be formed as a solid mass (COMPACT BONE) or in an open sponge-like manner (CANCELLOUS BONE)

Question 48

What is compact bone?

Answer 48

Is is made of parallel bone collumns which are disposed parallel to the long axis of the long bone. They are made of concentric (rings) bony layers (lamellae) arranged around a central channel with blood vessels, lymphatics and nerves (Haversain canals)

Question 49

How do the osteocyte communicate to one-another?

Answer 49

The Haversain canals with their lamella form the haversain systems (osteon). Neurovascular bundles interact with each other via Volkmann's canals that pierce the columns at right angles. Osteocytes in their lacunar communcate via the central canals cytoplasmic extensions called canaliculi.

Question 50

What is the relationship between compact bone and cortical bone?

Answer 50

The outermost layer of compact bone gives way to dense cortical bone in the centre. The compact bone acts as weight bearing pillars and are able to withstand high levels of mechanical stress. The innermost aspect of the compact bone, the lamellae erge with spongy bone.

Question 51

What is Cancellous bone?

Answer 51

Aka Spongy bone It is made of a network of bone trabiculae seperated by interconnected spaces containing BONE MARROW. Trabiculae are thin and composed of irregular bone lamellae. They dont contain haversain canals. The spongy nature is due to the marrow spaces, giving the bone flexibility.

Question 52

Alveolar bone features

Answer 52

1. Out and inner parellel alveolar plates 2. Sockets are separated by interdental septa 3. Roots are separated by interradicular septa

Question 53

How does bone remodelling change over time?

Answer 53

During childhood, bone deposition exceeds resorption. Equilibrium between deposition and resorption occurs n adult life. Resorption exceeds deposition in old age which leads to osteoporosis.

Question 54

What is the role of Osteoblasts in bone remodelling?

Answer 54

Osteoblasts can stimulate the production of osteoclasts by cytokine and growth factor release. Osteoblasts can produce osteoidase's which will expose the bone for osteoclast re-sorption.

Question 55

What are the hallmarks of bone remodelling?

Answer 55

Reversal lines make the change in bone activity; its a dynamic process as the bone is adapting to pressure. 25% of spongy bone mass is remodelled and 3% of compact bone every year.

Question 56

The Gingiva: What is the interdental Papilla?

Answer 56

The interdental gingiva occupying the area between adjacent teeth. Its size and shape depends ont he shape and contact between the teeth. Wedge shaped appearance on the buccal and lingual sides whilst pointed between anterior teeth.