Periodontium L7-9

Question 1

Functions of bone (x3)

Answer 1

1. Skeletal - protects organs; provides rigidity; allows attachment of muscles and teeth; movements
2. Container for marrow
3. Calcium pool

Question 2

How is bone involved in dentistry? (x5)

Answer 2

1. Regional differences in the mouth - local anaesthesia
2. Bone changes in the mouth - to extraction of teeth
3. Orthodontic tooth movements
4. Osseointegration - implants
5. Biphosphonates

Question 3

Composition of bone

Answer 3

60% mineral (largely hydroxyapatite); 25% organic substance; 15% water

Question 4

Breakdown of organic substances in bone

Answer 4

90% Type I collagen

10% ground substance

Question 5

Which bone is resorbed when the tooth is extracted?

Answer 5

Alveolar bone is resorbed

Basal bone stays

Question 6

Is the alveolar bone or the basal bone more suited for placement of dentures?

Answer 6

Alveolar bone - provides stability

Question 7

What is the outer layer of bone?

Answer 7

Cortical / Compact bone

Question 8

What is the inner layer of bone?

Answer 8

Trabecular bone / Spongy / Cancellous bone

Question 9

Name the 3 types of lamellae

Answer 9

1. Circumferential lamellae
2. Concentric lamellae
3. Interstitial lamellae

Question 10

Describe circumferential lamellae

Answer 10

Outside of most cortical bone; near the surface

Question 11

Describe concentric lamellae

Answer 11

Organised in Haversian systems/osteons; around a vascular core

Question 12

Describe interstitial lamellae

Answer 12

Remnants of old lamellae

Question 13

Name the 2 types of bone formation

Answer 13

1. Endochondral ossification

2. Intramembranous ossification

Question 14

What is endochondral ossification?

Answer 14

Cartilage –> Calcified cartilage –> Bone

Question 15

What is intramembranous ossification?

Answer 15

• Condensation of mesenchymal cells
• Osteoblasts - produce osteoid matrix
• Woven bone
• Primary osteon formation

Question 16

Role of osteoblasts

Answer 16

Produces osteoid matrix which then mineralizes

Question 17

What are osteocytes?

Answer 17

Trapped osteoblasts that are linked together by gap junctions

Question 18

Where can osteoclasts be found?

Answer 18

In howships lacunae

Question 19

Role of osteoclasts (x2)

Answer 19

1. Dissolves bone mineral - acid

2. Breakdown of organic matrix - enzymes

Question 20

Describe the roles of calcium in the body (x7)

Answer 20

1. Membrane permeability - decreases membrane permeability; decreases cell excitability; low calcium results in tetany
2. Excitation-contraction coupling
3. Excitation-secretion coupling
4. Hard tissue formation
5. Blood clotting
6. Enzyme reactions
7. In secretions - e.g. milk

Question 21

Mechanism of fast regulation of calcium

Answer 21

Rapid exchanges between bone and extracellular fluid

Question 22

Mechanisms of slow regulation of calcium (x2)

Answer 22

1. Intestinal absorption

2. Renal excretion

Question 23

When is the parathyroid hormone (PTH) released?

Answer 23

PTH is released in response to falling calcium level in plasma, increasing calcium levels by withdrawing calcium from the bone bank to prevent hypocalaemia.

Question 24

Describe the regulation of calcium levels by PTH

Answer 24

1. Fast calcium efflux to plasma from the small labile pool of calcium in bone - involves osteocytes - osteocytic osteolysis
2. Slow calcium efflux to plasma, involving bone dissolution - shifts remodelling to favour resorption and involves osteoclasts
3. Acts on kidneys to reduce excretion of calcium

Question 25

Describe the regulation of calcium levels by calcitonin

Answer 25

``` "C" cells act on thyroid gland and prevents calcium plasma levels from becoming high. Actions: - Reduce osteocyte activity - Reduce osteoclast activity - Reduce osteoclast numbers ```

Question 26

How does Vitamin D help in the regulation of calcium levels?

Answer 26

It increases absorption of calcium in the intestines

Question 27

Name a condition impacting the bones related to dentistry caused by medicines

Answer 27

Biphosphanates Related Osteonecrosis of the Jaws (BRONJ) | - caused by consumption of biphosphanates

Question 28

What are biphosphanates used for? (x2)

Answer 28

1. Osteoporosis - reduce fracture rates | 2. Bone metastases (secondary tumours in bone)

Question 29

Define tooth eruption

Answer 29

Tooth eruption is the movement of a tooth from its developmental position in the jaw to its functional position in occlusion in the mouth

Question 30

What are the two types of eruption?

Answer 30

Passive and active

Question 31

What is active eruption?

Answer 31

Bodily movement of the tooth

Question 32

What is passive eruption?

Answer 32

Uncovering of the tooth by apical gingival migration

Question 33

Describe the pre-eruptive movement of a tooth

Answer 33

The permanent successor starts off from a lingual/palatal position and move between the roots of its deciduous predecessors.

Question 34

What are the stages of eruption?

Answer 34

1. Pre-eruptive movements 2. Eruptive movements 3. Bloodless eruption 4. Deciduous exfoliation

Question 35

List the theories for tooth eruption (x7)

Answer 35

``` PUSH: 1. Root formation 2. Pulp proliferation 3. Bone formation 4. Fluid pressure PULL: 1. Collagen contraction 2. Fibroblast contraction 3,. Fibroblast migration ```

Question 36

Discuss evidence for and against root formation providing a "push" force for tooth eruption

Answer 36

for: Roots normally form during eruption against: - some teeth have eruption paths longer than root length (e.g. canines) - impacted teeth with fully formed teeth can erupt of impaction released (wisdom teeth)

Question 37

Discuss evidence for and against bone formation providing a "push" force for tooth eruption

Answer 37

for: Bone forms under an erupting tooth against: root is resected as teeth erupts and bone fills in as tooth moves away

Question 38

Discuss evidence for and against hydrostatic pressure providing a "push" force for tooth eruption

Answer 38

for: - periodontal vasculature - cervical sympathetic stimulation: vasoconstriction; cessation of eruption; reversible on cessation - sympathectomy: vasodilation - increased tissue pressure; increase eruption rate against: root resected rodent incisor erupt normally

Question 39

Which is the most plausible "push" factor for tooth eruption?

Answer 39

Hydrostatic pressures

Question 40

Which is the most plausible "pull" factor of tooth eruption?

Answer 40

PDL Fibroblasts

Question 41

Discuss evidence for and against collagen contraction providing a "pull" force for tooth eruption

Answer 41

for: collagen can contract in vitro against: no proof that collagen contracts in vivo (i.e. in the mouth)

Question 42

Discuss evidence for and against fibroblast migration/contraction providing a "pull" force for tooth eruption

Answer 42

for: fibroblasts show motility when cultured and they move cervically on eruption against: PDL fibroblasts do not have organelles for motility and there is no evidence that they can exert eruptive forces

Question 43

Describe the process of bloodless eruption

Answer 43

REE proliferates --> Fusion of oral epithelium and REE --> Epithelial cell death --> Epithelial pathway --> REE forms junctional epithelium

Question 44

Describe the process of deciduous exfoliation

Answer 44

Deciduous tooth must be resorbed to facilitate successional eruption. The pressure of tooth on bone results in resorption. Deciduous teeth are resorbed by odontoclasts (multinucleated osteoclast like cells derived from monocytes)

Question 45

Compare the tooth movements on loading between the horizontal and vertical plane

Answer 45

- greater movement of 100um in the horizontal plane | - lesser movement of 10um in the vertical plane

Question 46

What is the term used to describe tooth movement in response to load?

Answer 46

Visco-elastic system

Question 47

Maximum clenching forces between molars

Answer 47

500-700N

Question 48

State two factors that contribute to the viscosity in the visco-elastic tooth support

Answer 48

- ECM/ground substance | - periodontal fluids

Question 49

Name two factors that contribute to the elasticity component of the visco-elastic tooth support

Answer 49

- collagen | - bone

Question 50

Factors affecting tooth movement (x4)

Answer 50

Rate of load - slow rate, greater movement Longer the tooth is loaded - slower the rate of return to original position, more mobile it becomes If tooth is not loaded, becomes less mobile The more often the tooth is loaded, the more the tooth is displaced, the less mobile it becomes

Question 51

Features of the PDL supporting how it is like a tension bearing system x4

Answer 51

- oblique fibre orientation - sharpey fibres - fibroblast shape and orientation - chemistry of GAGs

Question 52

Features of PDL showing why it is unlike a tension bearing system x3

Answer 52

- small diameter of collagen fibres - sparsity of sharpey fibres in some parts of the lamina dura of the socket - quantities of ground substances (>50%)