y1 basic principles (study this)

Question 1

optical properties

Answer 1

3 parameters of colour
Hue (perceived colour)
Saturation (intensity)
Value (bright or dark)
Metameric colours = look the same under one light source but different under another
Fluorescence = material absorbs light energy of one wavelength and emits it at a different wavelength e.g. emitting fluorescent light under UV light

Question 2

electrical properties

Answer 2

Electrical conductivity = the ability to conduct an electric current

Galvanism = when 2 different metal restorations in contact, the different potentials set up an electric cell so causes a short circuit which causes pain

Question 3

formation of Ceramics

Answer 3

formed between metallic and non metallic elements

Question 4

general proeprties of ceramics

Answer 4

aesthetic, high melting point, low thermal exp. coefficient, strong, hard, mostly inert, brittle, fail by brittle fracture when a crack reaches a critical length

Question 5

types of ceramics

Answer 5

can be crystalline or non crystalline (crystalline has better mechanical properties and are less reactive)

Question 6

structure/ system of ceramics

Answer 6

There are 7 crystal systems/structures – e.g. simple cubic is the strongest and tetragonal is used for dental ceramics

Question 7

classification by microstructure

Answer 7

I. Glass - based (mainly)

II. Glass - based with crystalline fillers
bridges,

III. Crystalline - based with glass fillers

IV. Polycrystaline
all metals are polycrystalline
some ceramics like alumina and zirconia

Question 8

cystalline ceramics used in dentistry

Answer 8

Silica – comes in quartz, cristobalite, and tridymite forms (reconstructive transformations between these) and can have displacive transformations with changing temperature

Alumina – hexagonal, used for abrasives, fillers, implants

Hydroxyapatite – hexagonal, used for root canal filler,

Zirconia – different structures at different temps, similar uses to alumina

Gypsum – used for stone and plaster models

Zinc oxide – powder component of lots of cements

Porcelain – made from kaolin, feldspar, and quartz, used for veneers, inlays, crowns, bridges

Question 9

Non-crystalline ceramics in dentistry:

Answer 9

Feldspathic glasses
Fluoroalumunosilicate glasses
Diatomaceous earth

Fluxes can be used to reduce fusing temperature (e.g. borax). In general, the higher the fusing temperature of a ceramic, the higher the strength

Metal oxides can be added to give colour, opacity, fluorescence etc.

Glasses are non-crystalline materials formed when a high viscosity liquid is cooled rapidly (no time for crystals to form)

Question 10

general proeprties of metals and alloys

Answer 10

General properties

Polycrystalline

Conductors of heat and electricity

Good strength and high modulus (stiffness)

Lustre (shiny if polished)

Can corrode

All potentially toxic
Essential metals toxic if in high concentrations
Non-essential metals always toxic even in trace amounts

Question 11

why don’t you want dental metals to be corrosive

Answer 11

corrosion leads to degradation, ion release, ion migration around body, allergic/toxic phenomena.

Question 12

metals and alloys

types of corrosion

Answer 12

Types:
* Galvanic – between dissimilar metals
* Localised galvanic – between different phases within the same alloy
* Crevice – differences in surface oxygen levels
* Pitting – similar to crevice but occurs when passive oxide layer is damaged
* Stress - under sustained tensile force in corrosive environment

Question 13

describe the cooling curve of an alloy

Answer 13

• Metal alloys = a mix of 2 or more metals
• Improved properties over pure metals
• Liquidus temp (above this temp = all liquid, below this temp = liquid and solid)
• Solidus temp (above this temp = liquid and solid, below this temp = all solid)