DM3

Question 1

Describe the temperature in the mouth, is it body temperature?

Answer 1

• ◦ Cold drinks
• ◦ Hot food/drinks
• ◦ Thermal cycling (5°C to 60°C)

Question 2

Describe the pH variations?

1) plaque
2) acidic
3) alkaline

Answer 2

• ◦ Plaque (~pH4)
• ◦ Acidic drinks (pH 1-3)
• ◦ Alkaline medication (~pH 12)
• ◦ Toothpaste with chalk (~pH 12)

Question 3

What causes a material to fatigue?

Answer 3

low stess over time

Question 4

what sort of mechanical stress causes fracture?

Answer 4

high stress

Question 5

What can cause abrasion of the teeth? (3)

Answer 5

• ◦ Abrasive food
• ◦ Abrasive toothpaste
• ◦ Solvents causing softening (when things are soft, they are easier to scratch)

Question 6

How do bacteria effect restorations?

Answer 6

they break down resins

Question 7

define biocompatibility

Answer 7

Biocompatibility (put a material into the patients mouth, and in the application it is used in, it will do no harm)

Question 8

What mechanical properties do we need to consider of the set material?

Answer 8

◦ Strength, toughness, stiffness, hardness

Question 9

What Chemical properties do we need to consider of the set material?

Answer 9

Solubility, corrosion, leaching

Question 10

What thermal properties do we need to consider of the set material?

Answer 10

◦ Expansion/contraction

◦ Heat transfer (denture patient burn themselves)

Question 11

What adhesive property do we need to consider of the set material?

Answer 11

bonding of filling to tooth

Question 12

the efficacy (the ability to enduce the desired result) of a material depends on what properties (include which material this property applies to)?

Answer 12

1. safety (all)
2. accuracy ( very important in impressions)
3. Durability ( very important in restorations)
4. conservation ( very important in restorations)
5. prevention (longevity of “restored tooth” more important than the material
6. aesthetics (important for “visible” restorations

Question 13

What aesthetical properties do we need to consider?

2) What can affect the aesthetic of natural teeth?
3) How do we ensure we use a material that matches the aesthetic of the patient’s teeth
4) What other treatment can we provide that affects the aesthetic of all teeth (including natural)?

Answer 13

1) colour, shade, translucency, surface roughness, gloss
2) age changes colour
3) use shade guide
4) affected by polish

Question 14

For a material to be druable it must have a low what?

2) if its high what occurs insolvent?

Answer 14

1) low solubility

2) dissolution

Question 15

what is leaching?

2) When can it be good?
3) When does it have a negative effect?

Answer 15

1) loss of one component into a liquid
2) fluoride leaching (e.g. glass ion cement restoration)
3) plasticiser from polymers

Question 16

What material do we need to be weary of corrosion in?

2) Why is it such a problem?
3) WHat are the 5 consequences of 2?

Answer 16

metals and alloys

2) galvanic effects (2 or more metals, one anode and one cathode, have a different electrochemical potential with an electrolyte solution
3) loss of metal ions, weakening, change of appearance, releas of Sn (tin) =metallic taste in mouth, pain if release electrons go down pulp

Question 17

what is thermal expansivity?

Answer 17

the tendency of matter to change its shape, area, and volume in response to a change in temperature

Question 18

What is the coefficient of thermal expansion?

2) can you think of an equation in A level chemistry we learnt about that links to this?

Answer 18

The coefficient of thermal expansion describes how the size of an object changes with a change in temperature. Specifically, it measures the fractional change in size per degree change in temperature at a constant pressure
2) PV=nRT, the ideal gas equation

Question 19

What is the units of the coefficeitn of thermal expansion?

Answer 19

degrees celcius to the minus 1

Question 20

Compate the coefficient of thermal expansion of (a) a tooth with (b) acrylic resin, (c) amalgam, and (d) composite resin?

Answer 20

a) 11
b) 90
c) 25
d) 40

Question 21

what is thermal conductivity?

2) What is the equation
3) What is the units?

Answer 21

ability to conduct heat
2) Rate of heat flow = (llambda x area x temperature)/gradient distance
3) watts per square metre of surface area for a temperature gradient of 1 K per unit thickness of 1 m, Units = J s-1 m-1 °C -1
or W m-1 °C -1

Question 22

What is the thermal conductivity of enamel, dentine?

2) Which dental material has the highest thermal conductivity? what is it?
3) What is the thermal conductivity of acrylic resin and dental amalgam?

Answer 22

1) enamel= 0.92 Wm-1 °C -1 
dentine= 0.63 W m-1 °C -1 
2) gold, 291.70 W m-1 °C -1 
3) acrylic resin= 0.21 W m-1 °C -1 
amalgam= 23.02 W m-1 °C -1

Question 23

What is thermal conductivity and diffusivity important in dentistry?

Answer 23

When a patient gets dentures for the first time it is important to warn them not to scold themselves on hot drinks.

Question 24

1) What is thermal diffusivity?
2) What is the equation of thermal diffusivity?
3) what are the units?

Answer 24

Ability to react to sudden temperature stimulus/ Heat required to change temperature of body
before heat can be conducted
2) m2s-1

Question 25

What is heat capactiy?

2) What are the units?

Answer 25

1) ◦ Heat required to raise 1g of material by 1°C

2) Jg-1°C- -1

Question 26

What is force

Answer 26

Results from an outside agency acting upon a body to change its momentum

Question 27

What is the equation of force?

Answer 27

Force (N) = load (kg) x acceleration (ms-2 )

Question 28

Does a static load have a force?

Answer 28

yes, if under gravity i.e. Static load acts under gravity (e.g. 1 kg acting under gravity gives force of 9.8N)

Question 29

What is the magnitude of stress?

Answer 29

function of applied force and dimensions of the object to which force is applied

Question 30

1) What is tension?
2) What is compression?
3) What is shear?
… force?

Answer 30

1) material pulled apart e.g. force experienced by rope in tug of war
2) material pushed into itself e.g. force experienced by scales when object placed on top
3) unaligned forces pushing one part of a body in one specific direction, and another part of the body in the opposite e.g. force experienced by paper, when we rip apart

Question 31

What are the 2 main types of forces ?

2) What are their subtypes?

Answer 31

a) simple
b) complex
2) a) tensile, compressive and shear
2) flexural torsional diametral

Question 32

when si flexural stress experienced?

Answer 32

on bending, its a mixture of compressive and tensile

Question 33

whats the formula for simple stress?

2) what is the units?

Answer 33

1) force/area

2) Nm-2= Pa

Question 34

convert the following to Pa:

2. 3MPa
   b) 6.7 GPa

Answer 34

a) 2300000 (2.3 *10^6) Pa

b) 6700000000 (6.7 *10^9) Pa

Question 35

what is strength?

Answer 35

The maximum stress which can be withstood before breaking

Question 36

What is complex stress?

Answer 36

when 2 or more simple stresses are applied to a material

Question 37

What is :

a) torsional stress
b) diametral stress

Answer 37

torsional (twisting e.g. the skin during a Chinese burn), diametral (relating to cylinders or spheres)