Oral Biology: Hard Tissue Biology

Question 1

Label each arrow on the diagram

Answer 1

Question 2

What are the ideal properties of a tooth? (7)

Answer 2

1) Strong

2) Hard

3) Wear Resistant

4) Resistant to Chemical Damage

5) Ability to respond to insult/damage

6) Ability to repair

7) Aesthetic

Question 3

By weight, what are the percentages of mineral, matrix and water in Enamel? (%)

Answer 3

• 96% mineral
• 1-2% matrix
• 2% water

Question 4

By weight, what are the percentages of mineral, matrix and water in Dentine?

Answer 4

• 70% mineral
• 20% matrix
• 10% water

Question 5

By weight, what are the percentages of mineral, matrix and water in Cementum?

Answer 5

• 65% mineral
• 23% matrix
• 12% water

Question 6

By weight, what are the percentages of mineral, matrix and water in bone?

Answer 6

• 60% mineral
• 25% matrix
• 15% water

Question 7

What is the chemical formula for hydroxyapatite?

Answer 7

Question 8

Describe hydroxyapatite

Answer 8

• Hydroxyapatite has crytallites that are:
  
  • 70nm wide, 25nm thick and very long
  • Hexagonal cross-section
• OH- ion surrounded by 3 Ca²+ ions
• Surrounded by 3 PO4 3- ions
• Enclosed by 6 Ca²+ ions

Question 9

Hydroxyapatite can undergo ionic replacement (any ion can be substituted). F- may substitute OH-, what benefits to enamel arise from this?

Answer 9

• Stabilises the lattice
• More acid resistant
• F- and prevention

Question 10

List 8 facts about enamel

Answer 10

• covers anatomical crown
• epithelial product
• 96% inorganic hydroxyapatite
• 2mm thick max
• translucent
• non-vital
• hard (KHN 360-390)
• brittle

Question 11

Describe the basic structure of enamel in 3 points

Answer 11

• tightly packed hydroxyapatite crystals
• basic unit = enamel prism
• prisms visible in ground sections, SEM’s of acid etched enamel

Question 12

Which label is the enamel’s prism core and which label is the enamel’s prism sheath?

Answer 12

Question 13

Surface Enamel is different to subsurface enamel. List 5 characteristics of surface enamel

Answer 13

Surface enamel is:

• aprismatic (no prisms)
• slightly more mineralised
• higher levels of fluoride
• more resistant to acid attack/caries/erosion
• more resistant to acid etch

Question 14

What two types of high speed burs are capable of cutting through enamel?

Answer 14

• diamond
• tungsten carbide

Question 15

Which hard tissue is easily fractured with a hand instrument (e.g. a chisel), if unsupported?

Answer 15

Enamel

Question 16

What type of tissue is dentine?

Answer 16

Specialised connective tissue

Question 17

List 3 characteristics of dentine

Answer 17

• Hard (KHN 75)
• Strong and resilient
• ~ 79% mineral and 20% collagen

Question 18

What is pre-dentine and where is it located?

Answer 18

Predentine is non-mineralised tissue that lies beside the pulp

Question 19

Label this diagram - what are these dotted lines showing?

Answer 19

Direction of collagen fibres

Question 20

What does carious dentine feel like to the operator and how is it removed?

Answer 20

Carious dentine is soft, and is removed with a bladed bur or hand excavator

Question 21

What does sound dentine feel like to the operator and how is it removed?

Answer 21

Sound dentine is less hard than enamel, and is removed by either a high spped diamond bur or a low/high speed bladed bur

Question 22

Dentine is highly tubular. What structure are the tubules continuous with?

Answer 22

Tubules are continuous with the pulp - between 15,000 - 65,000 tubules per mm²

Question 23

What may tubules contain?

Answer 23

• cell processes
• nerves
• fluid - flows out

Question 24

Is dentine vital or non-vital?

Answer 24

Vital

Question 25

What is cementum and what is it’s purpose?

Answer 25

• Cementum is a mineralised specialised connective tissue
• Covers tooth roots
• To provide tooth support
• Resistant to resorption