W4: Biochemistry Of Bone And Teeth 1

Question 1

Function of skeleton/bones

Answer 1

Support, attachment, protection
Calcium homeostasis - store and metabolism
Dynamic tissue undergoing renewal and remodeeling

Question 2

Function of teeth

Answer 2

To tear and chew food - mastication
Speech
Facial cosmetic appearance
Defence/fighting
Tooth repair and regeneration

Question 3

Calcium store

Answer 3

• main body store is the skeleton. Ion exchange can occur at the mineral (hydroxyapatite) surfaces bathed in interstitial fluid

Question 4

Calcium metabolism

Answer 4

• plasma concentration is mainly under control of parathyroid hormone, calcitonin and vitamin D
• cells are key players in process of bone remodelling

Question 5

What happens if there is low dietary calcium?

Answer 5

Lower plasma Ca2+ concentration = increased PTH secretion =
- active vitamins D increasing intestinal calcium absorption
- decreased urinary calcium by conservation of dietary calcium
- bone loss from bone calcium release
All restore normal plasma calcium
LOOK AT ENDOCRINE?

Question 6

What types of cells are in bone?

Answer 6

Osteoblasts, osteocytes, osteoclasts

Question 7

Basic structure of a tooth

Answer 7

Enamel
Dentine
Pulp
Cementum

Question 8

Role of osteoblasts

Answer 8

Bone-forming cells: secrete the organic extracellular matrix of new bone (osteoid) which undergoes mineralisation to form bone. Osteoblasts become trapped in bone in lacunae as osteocytes and are responsible for maintaining the bone matrix.

Question 9

Role of osteoclasts

Answer 9

Large multinucleated cells responsible for bone resorption - degradation of the matrix to release calcium into bloodstream.
Fixes itself to the bone matrix with a lot of extensions and is able to dissolve the bone matrix and release calcium and other components.

Question 10

The bone remodelling cycle

Answer 10

There is a balance between bone resorption and formation.
Cells of osteoprogenitor cells differentiate into specialised cell types.
Cells differentiate into osteoclasts which then fuse to become multinucleated cells and resorb bone. Usually brittle and old bone.
Cells move away and osteoblasts are differentiated into. They produce bone to compensate for the amount resorbed. Then osteoblasts become inactive and lining cells.

Question 11

Regulation of bone remodelling

Answer 11

Local regulatory factors might promote the formation of osteoclasts which might resorb the bone and release growth factors which stimulate formation of osteoblasts
Osteoblasts can also release growth factors which stimulate the formation of osteoclasts
Complete feedback

Question 12

Which cells are osteoclasts derived from?

Answer 12

Haematopoietic stem cells pools. Monocytic macrophage family,

Question 13

What cells are osteoblasts derived from?

Answer 13

From mesodermal derived cell types, mesenchymal stem cell pools. Connective tissue type cells.

Question 14

2 forms of bone

Answer 14

Woven bone and adult lamellar bone

Question 15

What is woven bone

Answer 15

Immature bone, with random organisation of its collagen. Present during early development - fracture repair, healing tooth sockets etc. Gradually replaced and remodelled by mature bone.

Question 16

What is adult lamellar bone?

Answer 16

Composed of successive layers of bone:

• compact bone (dense)
• cancellous or trabecular bone (open spongy-like bone, porous)

Question 17

What is compact bone made of?

Answer 17

Circumferential and concentric bone layers (lamellae)
Concentric lamellae are arranged around a central channel with blood vessels, lymphatics and nerves = Haversian canal
Osteons (haversian systems) form the main structural bone units
Osteocytes in their lacunae interact with each other and with the central canal via canaliculi
The outermost layer of compact bone gives way to dense cortical bone
Lamellae merge with trabecular of cancellous bone

Question 18

What are osteocytes responsive to?

Answer 18

Mechanical loading, where they then regulate osteoblasts and osteoclasts
Role in tooth movement

Question 19

How does compact bone act as weight bearing pillars?

Answer 19

• biomechanicsl function

- able to withstand high levels of mechanical stress

Question 20

Cancellous/trabecular bone composition

Answer 20

Network of bone trabeculae separated by interconnected spaces contains bone marrow
Thin and composed of irregular bone lamellae
Osteocytes are linked to blood sinusoids in the marrow via canaliculi
Trabeculae are aligned along lines of stress as to withstand forces applied to the bone while adding minimally to the mass

Question 21

Hard mineralised tissues of the tooth

Answer 21

Enamel, dentin, cementum

Question 22

What is enamel?

Answer 22

The hardest and most highly mineralised tissue in the body.

Question 23

Properties of enamel

Answer 23

Mature enamel is acellular (no cells) - not living/non-vital
Insensitive
Cannot be regenerated

Question 24

Structure of enamel

Answer 24

Prismatic structure: millions of calcium hydroxyapatite crystals are packed to form rods/prisms

Question 25

Properties of dentine

Answer 25

Rigid but elastic and resilient so ideal to support brittle enamel
Tubular structure
Vital, permeable and sensitive
Formed throughout life
Pre dentine is the freshly laid down dentine prior to mineralisation
Capable of repair

Question 26

What cells secrete the dentine matrix?

Answer 26

Lining the pulp is a layer of odontoblasts which secrete the dentine matrix - dentine forming cells

Question 27

Types of dentine

Answer 27

Primary dentine formed during embryonic development, before the tooth is erupted and before tooth development
Secondary denting forms after tooth becomes functional and complete root development
Tertiary dentine is a repair response from odontoblasts/pulp cells to external stimuli or assaults (e.g., caries)

Question 28

Dentine repair - reactionary

Answer 28

Reactionary process: minor injury to the tooth causes stimulation of odontoblasts to form more dentine, aiming to protect and seal off the viable dental core. Produces tertiary dentine formation.

Question 29

What are the postnatal pulp stem cells?

Answer 29

Reservoir of cells for new odontoblasts
Peri vascular cells
Undifferentiated mesenchymal cells/fibroblasts
Specific stem cell population

Question 30

Function of cementum

Answer 30

Prime function of cementum is to give attachment of the tooth to collagen fibres of the periodontal ligament.

Question 31

Properties of cementum

Answer 31

Similar to bone in chemical composition and properties but is avascular and not innervated. Can be repaired and regenerated thus helping maintain the integrity of the root structure.

Question 32

What is the inorganic component of bone?

Answer 32

Hydroxyapatite crystals: minerals

Question 33

What is the organic component of bones and teeth?

Answer 33

Extracellular matrix: proteins. E.g., collagen, glycoproteins and proteoglycans

Question 34

Composition of bone, dentine and cementum

Answer 34

• mesodermal/(ecto)mesenchymal origin
• composed of collagenous calcified matrix
• 60-70% inorganic, 20% organic, 10% water

Question 35

Composition of enamel

Answer 35

• ectodermal - epithelial origin

- composed of 96% mineralised component

Question 36

Physical characteristics of bone, dentine and enamel

Answer 36

Bone and dentine are hard with elastic properties

Enamel is very hard but brittle

Question 37

Do dentine and cementum take part in calcium homeostasis?

Answer 37

They are calcified tissues but do not take part in the ion exchange. Enamel does.

Question 38

What are osteocytes?

Answer 38

Living/viable cells. As long as the bone is bone is viable, the osteocytes are viable.

Question 39

What does bone remodelling ensure?

Answer 39

That the bone remains renewed and viable. E.g.m if there is a micro fracture or bones are old, osteoclasts can remove this and osteoblasts can fill the resorption with fresh bone.

Question 40

Dentine repair - reparative

Answer 40

Reparative dentine formation: major tooth decay causes progenitor cells to differentiate into new odontoblasts which then produce tertiary dentine formation.