Dental hard tissues

Question 1

Examples of mineralised (hard) tissues

Answer 1

Alveolar bone, cementum, dentine and enamel

Question 2

Examples of non- mineralised (soft) tissues

Answer 2

Oral mucosa, dental pulp, gingivae, periodontal ligament

Question 3

Colour of dentine

Answer 3

Pale yellow

Question 4

Organisation of dentine

Answer 4

Fine, parallel tubules within a collagenous matrix, tubules are S shaped (primary curvature), tubules connect pulp chamber to enamel and dentine junctions, contain long processes of cell bodies (odontoblasts), dentine at the junction is unmineralised and known as predentine

Question 5

Is dentine vital or non vital

Answer 5

Vital

Question 6

Function of dentine

Answer 6

Acts as a shock absorber - dissipating large loads throughout the tooth structure

Question 7

Composition of dentine

Answer 7

70% inorganic
20% organic
10% water

Question 8

Sigmoid route of dentine

Answer 8

Primary curvature - Schreger lines

Question 9

What is dentine between tubules called

Answer 9

Intertubular dentine

Question 10

Small changes in direction of dentine

Answer 10

Secondary curvature - Lines of Owen

Question 11

When does secondary dentine appear

Answer 11

After completion of tooth and root formation

Question 12

What is translucent dentine

Answer 12

Forms with ageing

Caused by tubule occlusion by deposits of peritubular dentine

Question 13

What is tertiary dentine

Answer 13

Occurs in reaction to a pathological change

Question 14

Different types of tertiary dentine

Answer 14

Reactionary: Formed in response to injury/ insult. Made from existing odontoblasts
Reparative: Formed in response to a stimulus. Made from new plural progenitor cells

Question 15

What is sclerotic dentine

Answer 15

Tubule occlusion by an external stimulus

Question 16

What are dead tracts

Answer 16

Odontoblasts are killed by an external stimulus, or retract leaving empty tubules

Question 17

What is peritubular dentine

Answer 17

Located in the wall of tubules

Question 18

What is intertubular dentine

Answer 18

Located between tubules

Question 19

What is mantle dentine

Answer 19

Outermost layer, 1st dentine formed

Question 20

What is circumpulpal dentine

Answer 20

Located around the pulp - bulk of dentine

Question 21

What is primary dentine

Answer 21

Formed prior to root completion. Formed more rapidly and more mineralised than secondary dentine

Question 22

What is secondary dentine

Answer 22

Formed after completion of root and tooth formation, formed more slowly and is less mineralised than primary dentine

Question 23

What are lines of von ebner

Answer 23

Represent cyclic activity of odontoblasts during dentine formation
5-6 um per day - crown
3.5 um per day - root

Question 24

What are ameloblasts

Answer 24

Enamel producing cells

Question 25

Where is enamel thickest

Answer 25

Cuspal/ incisal regions

2.5mm @ thickest point

Question 26

Hardness index (knoop no) of enamel and dentine

Answer 26

Enamel - 296

Dentine - 64

Question 27

Composition of enamel

Answer 27

96-97% inorganic

3-4% organic

Question 28

Structure of enamel

Answer 28

Organised into rods (prisms)and interiors
Built from closely packed hydroxyapatite crystals
Hexagonal symmetry
Rod = cylinder shaped
Organisation is tighter around the centre of each rod

Question 29

What are striae of retzius

Answer 29

A series of dark lines extending from the DEJ towards the surface of the tooth
They form due to a weekly rhythm of enamel production resulting in structural alterations of the rods

Question 30

What are bands of hunter and schreger

Answer 30

They are produced by the changing orientations of adjacent groups of rods

Question 31

What is gnarled enamel

Answer 31

Where the rods appear twisted around in each other in a complex arrangement

Question 32

What is perikymata

Answer 32

Transverse waves like grooves, external manifestations of striae of retzius