DM3 Flashcards
Describe the temperature in the mouth, is it body temperature?
- ◦ Cold drinks
- ◦ Hot food/drinks
- ◦ Thermal cycling (5°C to 60°C)
Describe the pH variations?
1) plaque
2) acidic
3) alkaline
- ◦ Plaque (~pH4)
- ◦ Acidic drinks (pH 1-3)
- ◦ Alkaline medication (~pH 12)
- ◦ Toothpaste with chalk (~pH 12)
What causes a material to fatigue?
low stess over time
what sort of mechanical stress causes fracture?
high stress
What can cause abrasion of the teeth? (3)
- ◦ Abrasive food
- ◦ Abrasive toothpaste
- ◦ Solvents causing softening (when things are soft, they are easier to scratch)
How do bacteria effect restorations?
they break down resins
define biocompatibility
Biocompatibility (put a material into the patients mouth, and in the application it is used in, it will do no harm)
What mechanical properties do we need to consider of the set material?
◦ Strength, toughness, stiffness, hardness
What Chemical properties do we need to consider of the set material?
Solubility, corrosion, leaching
What thermal properties do we need to consider of the set material?
◦ Expansion/contraction
◦ Heat transfer (denture patient burn themselves)
What adhesive property do we need to consider of the set material?
bonding of filling to tooth
the efficacy (the ability to enduce the desired result) of a material depends on what properties (include which material this property applies to)?
- safety (all)
- accuracy ( very important in impressions)
- Durability ( very important in restorations)
- conservation ( very important in restorations)
- prevention (longevity of “restored tooth” more important than the material
- aesthetics (important for “visible” restorations
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)?
1) colour, shade, translucency, surface roughness, gloss
2) age changes colour
3) use shade guide
4) affected by polish
For a material to be druable it must have a low what?
2) if its high what occurs insolvent?
1) low solubility
2) dissolution
what is leaching?
2) When can it be good?
3) When does it have a negative effect?
1) loss of one component into a liquid
2) fluoride leaching (e.g. glass ion cement restoration)
3) plasticiser from polymers
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?
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
what is thermal expansivity?
the tendency of matter to change its shape, area, and volume in response to a change in temperature
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?
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
What is the units of the coefficeitn of thermal expansion?
degrees celcius to the minus 1
Compate the coefficient of thermal expansion of (a) a tooth with (b) acrylic resin, (c) amalgam, and (d) composite resin?
a) 11
b) 90
c) 25
d) 40
what is thermal conductivity?
2) What is the equation
3) What is the units?
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
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?
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
What is thermal conductivity and diffusivity important in dentistry?
When a patient gets dentures for the first time it is important to warn them not to scold themselves on hot drinks.
1) What is thermal diffusivity?
2) What is the equation of thermal diffusivity?
3) what are the units?
Ability to react to sudden temperature stimulus/ Heat required to change temperature of body
before heat can be conducted
2) m2s-1
What is heat capactiy?
2) What are the units?
1) ◦ Heat required to raise 1g of material by 1°C
2) Jg-1°C- -1
What is force
Results from an outside agency acting upon a body to change its momentum
What is the equation of force?
Force (N) = load (kg) x acceleration (ms-2 )
Does a static load have a force?
yes, if under gravity i.e. Static load acts under gravity (e.g. 1 kg acting under gravity gives force of 9.8N)
What is the magnitude of stress?
function of applied force and dimensions of the object to which force is applied
1) What is tension?
2) What is compression?
3) What is shear?
… force?
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
What are the 2 main types of forces ?
2) What are their subtypes?
a) simple
b) complex
2) a) tensile, compressive and shear
2) flexural torsional diametral
when si flexural stress experienced?
on bending, its a mixture of compressive and tensile
whats the formula for simple stress?
2) what is the units?
1) force/area
2) Nm-2= Pa
convert the following to Pa:
- 3MPa
b) 6.7 GPa
a) 2300000 (2.3 *10^6) Pa
b) 6700000000 (6.7 *10^9) Pa
what is strength?
The maximum stress which can be withstood before breaking
What is complex stress?
when 2 or more simple stresses are applied to a material
What is :
a) torsional stress
b) diametral stress
torsional (twisting e.g. the skin during a Chinese burn), diametral (relating to cylinders or spheres)
