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Restorative > Porcelain > Flashcards

Porcelain Flashcards

0
Q

What is in kaolin?

A

Al2o3. 2sio2. 2H2O

Hydrated aluminosilicate

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1
Q

What are the components of porcelain?

A

Kaolinite
Quartz
Feldspar

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2
Q

What is quartz made from?

A

SiO2

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3
Q

What is the most common element in the earth?

A

Silica

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4
Q

What is feldspar?

A

Mixture of potassium and sodium aluminosilicates

K20 Al2O3 6SiO2
N20

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5
Q

What are dental porcelains mainly composed of?

A

mainly Felspar some quart hardly any qaolin

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6
Q

What is the differnce in compostition of high fusing and low fusin porcelain?

A

percetntage: Kaolin, Silica, Feldpar, Glasses
High fusing: 4, 15, 80, 0
Low fusing:, 25, 60, 15

Metal oxides less than 10%

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7
Q

Wen are high fuse porcelains used?

A

they are used mainly for PJC

they fuse at around 2400 degress

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8
Q

When are low fuse porcelains used?

A

these are used to provide the glaze

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9
Q

What are the other componenents added to porcelain?

A

Borax: sodium borate

Metal oxides

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10
Q

What is the purpse of adding sodium borate, and to what component is it added to?

A

this is added to feldspar

added to reduce melting temp

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11
Q

What are the two types of metal oxides added for?

A

pigments and opalscence

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12
Q

Which metal oxides are added for pigmentation?

A

iron: brown
copper: green
coablt: blue

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13
Q

Which metal oxides are added for opalscence *transparity?

A

Zno

Titanium oxide

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14
Q

What are the physical properties of porcelain?

A

Low thermal conductivity: good since does conduct heat to pulp, bad since thermal stresses can lead to fracture
Excellent aesthetcs
wide range of shades so can mimic dentine and enamel

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15
Q

What determines the opacity or trasparency of porcelains composte and ceramic materials?

A

partcle size and index of refraction of the differnt components

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16
Q

WHat was the issue with having kaolin in porcelain?

A

it was initally added to increase the abilty to mould and shape the porcelain however, since it was opaque it made it difficlt to achieve a high transluceny of porcelain

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17
Q

What are the chemical and biological properties of porcelain?

A

bicompatoble
stable
need to ensure that porcelain is glazed since only polishing makes the surface quite rough and promotes plaque accumulation

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18
Q

t/f porcelain is harder than enamel?

A

t

vickers hardness is 450 vs 350 for enamel

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19
Q

What are the mechanical properties of procelain?

A

brittle
lacks fracture toughness
fails via catostrophic failure and static fatigue

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20
Q

What are is static fatigue?

A

decrease in strength over time even in the abscence of load but is accelrated by dynamic loading

SiO bonds slowly hydrolysed and this genreats a rise in OH which elevates pH. this then dissolves oout the Na2O and the K2O (feldpsathic components)

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21
Q

WHat is catostrphoc failure?

A

this is when the porcelain actually chips away and due to its brittle nature and is rapid.

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22
Q

How is the stength of the porcelain reduced?

A

surface roughness
internal voids
porosity

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23
Q

How can the mechaical properties of porcelains be improved?

A
  1. Alter processing: optimising the fabrication condition
  2. produce stronger procelains: optimising the compostions and microstructure
  3. Reinforce porcelain by providing a solid core : structure optimisation
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24
Q

What are the 5 processing imprvments?

A

Careful tooth prep: redices stresses inside the crown
Use finer grain powder: gives a more unifrom microstructure and surface
Fire at vacuum or under pressure: reduces porosity
Cool slowly from furncae: reudces thermal stresses which can cause cracks
Smooth or further fusing: reduces surface roughness and imprefections

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25
Q

WHat are the three ways of priducing stronger porcelains?

A

most common method of failure is via crack propagation from the surface irregularties so need a compressive strenght to combat the froces created at surface imperfections

  1. Ion exchange: xreates compressive forces all over surface by soacking the fired porcelain in molten potassium salt
  2. thermal stengthening: careful applicaton of heat during inital firing or later heat tempering.
  3. adding strengthening particles:alumina added will act as crack stoppers. plate like mica or needle like crystals eg lithium disiclicate are added
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26
Q

What are the names of the various stengthening cores that can be added?

A 
alumina
alumina reinforces feldspathic porcelain
glass infiltrated alumina
spinel
zirconia
27
Q

WHat are the advnatages of porcelain?

A

aestehtics

chemically inert

28
Q

Wgat are the disadvntages of porcelain?

A

brittle (low fracture toughness)
High elastic modulus
high vicker hardness so wear to enamel

29
Q

How do you prepare porcelains?

A

Powder mixed with water and a binder
moulded and carved and the compacted and dried
fired and cooled
glazed or poloshed

30
Q

WHat is the name of the porcelain powder?

A

a frit

31
Q

How is rhe frit made?

A

feldspar
kaolin
silica
ground up, mixed and fused *fedpar acts as the flux. rapidly cooled and then ground again

32
Q

What is the binder?

A

this is made from sugar and starch so improves the working time of the porcelain

33
Q

What do we place the porcelain on when firing?

A

placed on to foil mould and the porcelain shrinls towards this and assures a god fit of the crown to the tooth

34
Q

what is the purpose of compating?

A

light vibrations and patting whichsettles the partciles and reduces shirnkage. this gives a uniform contraction over the whjole surface and brings any excess water to the surface.

35
Q

What do modern mnufactures use to make green dense ceramics?

A

cold isotatic pressing

36
Q

How are drying and sintering carried out>

A

plced in warm atmosphere less than 100 degrees
since if wet procelain placed straight into hot oven it will bloat. once dried at lower temperature, it is then fired at a high temperature by placing in a firnace of more than 1000 degrees sometimes under vaccuum

37
Q

How is glazing performed?

A

Low fusing transparent glass is used to coat the porcelain and improves the appearance provding greater translucency
this proves a smooth impervous finsih protecting agaisnt chemica attack and lowering hardness to reduce wear

38
Q

Which component to porcelain has the lowest melting point?

A

Feldspar

Acts as a flux

39
Q

T/Fporcelaim is strong in compression?

A

T

40
Q

T/f porcelain is week I tension?

A

T

This is why cannot be used in thin section

41
Q

What is the name for the feldpathic components?

A

Soda Na2Oand potash K2O

42
Q

T/F porcelain is a thermal insulator?

A

T

43
Q

What is a glaze?

A

Glass put on the surface

44
Q

What is the purpose of the porcelain glaze?

A

Smooths the surface

Protects against chemical attack

45
Q

What temp are core porcelains fired at?

A

850-1050 for 5 mins

46
Q

What temp are the enamel and dentine porcelains fired at?

A

750-900 for 5 mins

47
Q

By how much does porcelain shrink after firing?

A

40%

48
Q

What are the options for sintered porcelains?

A

Aluminous porcelain: this is strong and used for cores but not great aesthetics since more opaque
Feldpathic reinforces with zirconia or leucite

49
Q

How do you prepare for a PJC?

A

Incisal reduction by 1/4 or 1/3
Labial reduction in two planes
5% taper
Even Palatal reduction

1mm shoulder

50
Q

What are resin bonded crowns?

A

Made in feldpathic porcelains
Minimally intervention
Thin section

Strength derived from underlying bond to tooth

51
Q

What are the ad and dis of PJVC?

A

AD: good aesthetics and easy to manufacture
Dis: abrasive, brittle, irreversible ,damaging to tooth

52
Q

What is good about PFM?

A

Strength of metal restoration and Appearance of porcelain

53
Q

When are PFM indicated?

A

Heavy masticatory load
Limited Palatal space
Incorpated rest seat

54
Q

What are the dis of PFM?

A

Destructive
Difficult to remove
Cost
Technqie sensitve

55
Q

How does metal bond to porcelain?

A

Early theory: van der waals, setting

Now: mechanical interlocking, chemical bond to oxide layer, compressive force

56
Q

What are the causes of failure for PFM?

A

Insufficient metal support
Unequal thickness of porcelain
Faulty design
Fault occlusion

57
Q

What should you avoid with PFM?

A

Unsupported porcelain

Interfaced of porcelain and metsl under heavy occlusal load

58
Q

What is the function of a Pontic?

A

Appearance
Stabilise occlusion
Masticatory
Phonetics

59
Q

What are the options for a bridge replacing anterior tooth?

A

Conventional fixed fixed
Cantilever bridge
Spring cantilever
RRB

60
Q

When preparing the labial preparation phases?

A

2 stages
First cut is incisal third
Second cut: gingival third

61
Q

What type of preps are there for PFM?

A

Winged prep : more resistance and more conservative

Wingless Prep : easier to prepare, less chance of leaving undercut

62
Q

What is the depth of the PFM shoulder?

A

1.3mm

63
Q

How deep is the Palatal chamfer?

A

0.7mm

64
Q

What are the stages of bridge prep for anterior teeth?

A 
Incisal reduction by 2mm
Paired mesial and sitar prep 
Paired axial prep
Cingulam reduction of 1mm 
Shoulder 
Finnish

Restorative (45 decks)

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