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Year 3 Operative and endo > Porcelain and Ceramics > Flashcards

Porcelain and Ceramics Flashcards

1
Q

clinical uses of ceramics in dentistry

A

crowns
veneers
onlays
bridges

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2
Q

difference between ceramic and porcelain

A

ceramic: inorganic, non-metallic materals

porcelain is a type of ceramic

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3
Q

name/ components of compositions of ceramic

A

KQF kian’s qute as fuck
I: kaolinite (kaolin). china clay, hydrated aluminosilicate
II: quartz, silica (SiO2)
III: Feldspar. mixture of potassium and sodium aluminosilicates

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4
Q

% composition of high-fusing dental porcelain

A

80% feldspar
15% silica
4% clay

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5
Q

% composition of low-fusing dental porcelain

A

60% feldspar
25% silica
15% glasses

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6
Q

what materials contain mainly clay/ quartz?

A

earthenware, stoneware (pottery etc)

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7
Q

minor components of porcelain and their function

A
  • borax (sodium borate): added to feldspar, reduces melting point
  • metal oxides. 2 functions:
  • -pigments eg iron (brown), copper (green), cobalt (blue)
  • -opalescence eg zinc oxide, titanium oxide
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8
Q

physical properties of porcelain

A
  • good aesthetics, wide range of shades and translucencies to mimic natural tissues
  • low thermal conductivity
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9
Q

why is low thermal conductivity good AND bad?

A

good: does not conduct heat to pulp
bad: thermal stresses lead to cracks/ fatigue

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10
Q

3 influences on translucency of porcelain

A
  1. grain size
  2. metal oxides (zinc oxide, titanium oxide)
  3. index of refraction
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11
Q

chemical and biological properties of porcelain

A
  • stable
  • biocompatible
  • polished surface rougher than glazed surfaces –> may accumulate more plaque
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12
Q

mechanical properties of porcelain

A

low fracture resistance (brittle)
low tensile strength
hard

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13
Q

2 failure models of brittle materials

A
  1. catastrophic failure

2. static fatigue (over time, even in absence of load)

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14
Q

3 factors that reduce strength of a material

A

surface roughness
internal voids
porosity

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15
Q

why does static fatigue happen

A

Si-O bonds slowly hydrolysed

–> generates OH- –> increased pH –> dissolves Na2O and K2O (in feldspath) –> forms pores

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16
Q

true or false: static fatigue is the same regardless of loading

A

false. it happens both with and without loading but it is accelerated by dynamic mechanical loading

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17
Q

how to improve mechanical properties of ceramics 3

A
  1. alter processing (optimise fabrication condition)
  2. produce stronger porcelain (composition and microstructure)
  3. structure: reinforce with solid, supportive core
18
Q

methods of improving processing 5

A
  1. use fine grain powder –> more even microstructure/ surface
  2. reduce porosity (fire in vacuum or under pressure)
  3. reduce thermal stress to reduce cracks (cool slowly after removing from furnace
  4. reduce surface roughness/ imperfections (smoothing or further fusing)
  5. reduce poss for stress at inner surface of crown (careful tooth prep)
19
Q

what is the most common failure of porcelain

A

surface irregularities at INNER surface of crowns –> crack propagation

20
Q

what is needed to counteract this? how is this achieved (3)

A

compressive strength
1. ion exchange strengthening: soak fired porcelain in molten potassium salt to create compressive forces all over surface

  1. thermal strength: careful application of heat during initial firing or later heat tempering to stop compressive stress caused by liquid centre of porcelain before it sets
  2. particulate strengthening/ toughening: stop crack propagation. alumina, lithium disilicate (needle like), mica (plate like)
21
Q

5 materials added to achieve strong ceramic core

A
  1. alumina
  2. alumina-reinforced feldspath porcelain
  3. glass-infiltrated alumina
  4. spinel (magnesium aluminate)
  5. zirconia
22
Q

flowchart of preparation of porcelain

A

mix powder, water and binder

  • -> mould, carve
  • -> compact, dry
  • -> fire, cool
  • -> glaze, polish
23
Q

how is porcelain supplied

A

as powder or frit

24
Q

stages other materials must go to

A 
ground
mixed
fused
rapidly cooled
ground again
25
Q

function of feldspar

A

lowest melting temp –> fuses other materials together

26
Q

what is used as a binder and why

A

sugar or starch. improves working properties

27
Q

what material is used for the mould when making traditional crowns and why

A

platinum
not affected by firing temp, porcelain shrinks inwards towards foil
–> assures fit of crown on tooth

28
Q

function of compaction of porcelain 3

A
  1. settles particles –> reduces shrinkage
  2. gives uniform contraction over whole surface
  3. bring excess water to surface
29
Q

2 methods of contraction

A
  1. light vibrating/ patting

2. cold isomatic pressing (CIP) to make dense ‘green’ porcelain ceramics

30
Q

order of sintering process

A

(drying and firing)

1. placed in to warm atmosphere to dry (1000C), sometimes in vacuum

31
Q

what happens if wet porcelain is put straight in to oven

A

it will bloat

32
Q

what is used as glazing

A

low-fusing transparent glass

33
Q

3 functions of glazing

A
  1. improves appearance –> greater translucency
  2. gives impervious, smooth coating –> prevents chemical attack
  3. lower hardness –> reduce wear
34
Q

3 main categories of porcelain bonding

A
  1. cemented using luting agents
  2. fused to metal then cemented to tooth
  3. resin-bonded ceramics (recent)
35
Q

why is PFM used

A

good mechanical and aesthetic properties (gd parts of porcelain and metal)

36
Q

4 alloys used in PFM

A

high-gold
low-gold
silver-palladium
nickel-chromium

37
Q

3 types of ceramic

A

crystalline
amorphous (glass)
mixture (glass-ceramics)

38
Q

cost of a crown to a pt

A

£300-400

39
Q

are porcelains damaging to environment?

A

no- materials plentiful

40
Q

longevity of crowns

A

10 yrs

41
Q

time consumption of crown making

A

several visits, quicker due to CAD CAM

42
Q

h&s concern of porcelain

A

fine powders –> use extractor

Year 3 Operative and endo (6 decks)

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