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YR 3 - CSB > FIXED PROS - Materials for Crowns and Bridgework > Flashcards

FIXED PROS - Materials for Crowns and Bridgework Flashcards

1
Q

what should the choice of materials ensure with the patient? (4)

A
  • cosmetic expectation
  • no excessive removal of sound tissue
  • there is no adverse contact with tissue
  • meet the relevant standards
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2
Q

what requirements should the material meet? (6)

A
  • accurate fit
  • strong to resist occlusal force
  • similar thermal expansion as the tooth
  • should not attract plaque
  • biocompatible
  • be rigid to avoid bending
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3
Q

what options are there for crown and bridge materials?

A

metal
ceramics
metal-ceramics - porcelain+metal
indirect dental composite

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4
Q

what are the two types of metal alloys used?

A

precious alloys - gold and palladium alloys

non-precious alloys - base metal alloys - nickel and titanium

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5
Q

how do you decide what material to use? (7)

A
  • cost
  • corrosion resistance
  • strength
  • hardeness
  • stiffness
  • ductility - deform
  • location
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6
Q

describe a gold crown from LDI

A

1 star
medium-gold casting alloy - gold, silver, platinum.
yellow
extra-hard

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7
Q

why is Gold used as an alloy? (4)

A

tarnish-free
corrosion resistant
adds good malleability to an alloy
increases density

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8
Q

why is Copper used as an alloy? (2)

A

strengthener
enhances the colour with reddish colour

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9
Q

why is Silver used as an alloy? (3)

A
  • balance reddening from copper
  • adds greenish colour
  • controls strength and hardness
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10
Q

why may you not use pure gold?

A

too soft, costs

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11
Q

what is the common alloy used?

A

Ag-Au-Cu
gold, silver, copper

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12
Q

what if there isn’t enough gold?

A

density is reduced

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13
Q

what if there is too much palladium or silver?

A

they absorb oxygen when molten = porous castings

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14
Q

why may base metal alloys be preferred to use over precious alloys? give one con in comparison.

A

have higher modulus elasticity = more rigid and stiff

  • need careful controlled casting conditions, hinders the biocompatibility
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15
Q

define material biocompatibility.

A

the ability of a material to perform with an appropriate host response in a specific application

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16
Q

what is the biggest downside of having high levels of NICKEL? and one other side effect lol.

A

its carcinogenic

  • well known to cause contact dermatitis
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17
Q

the fumes from grinding and casting alloys can lead to? (3)

A

conjunctivitis
dermatitis
bronchitis

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18
Q

why may you use porcelain fused to metal?

A

have the benefits of metal and aesthetic benefits of ceramic

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19
Q

what is the success rate of porcelain fused to metal materials?

A

95-97% over 7 years

20
Q

does porcelain bond better to non precious metals, or precious metals?

A

precious metals

21
Q

in PFM (porcelain fused to metal) alloys, Indium is a metal which also may be used, why?

A

it strengthens and hardens gold and palladium
- by raising the thermal expansion
- lowering the melting range
- contributes to bonding oxide

22
Q

what are gold alloys called? and what are the PFM alloy called?

A

gold alloy - 1 star casting alloy

PFM - V-Delta SF Alloy

23
Q

which has higher density? the gold alloy or PFM?

A

PFM - V-Delta SF Alloy

24
Q

which has higher melting range? the gold alloy or PFM?

A

PFM - V-Delta SF Alloy
= 1180-1300

gold = 840-875

25
Q

how do you achieve a good bond between metal and ceramic? (3)

A
  • mechanical retention - roughen the metal
  • direct chemical bond - add Indium
  • mismatch the coefficient of thermal expansion - metal higher then ceramic = creates a compressive stress
26
Q

why may PFM alloys not be ideal? (4)

A
  • absence of light transmission - light doesnt pass through metal
  • reduced depth of translucency
  • so grey line at gingival margin
  • can have sensitivity or allergies
27
Q

what can be the downside of non-precious metal alloys?

A

discolouration over time

28
Q

for aesthetics, what is the gold standard?

A

all ceramic material and no metal

29
Q

what property do ceramic materials posses?

A

brittleness - need to be very careful

breaking point is 0.1% of strain

  • they dont bend, they break
30
Q

what is the Griffith Equation?

A

the failure stress = fracture toughness/flaw size

31
Q

using the Griffith Equation, how may you increase the fracture toughness?

A

increase the failure stress
reduce the flaw size

32
Q

why is it better to use ceramic rather than glass?

A

more resistant to cracks leading to complete failure due to crystalline domains

33
Q

what is Alumina Porcelain?

A

porcelain containing up to 50% fused alumina crystals

34
Q

what is the benefit of adding alumina crystals to porcelain?

A

it acts as a crack stopper
adding strength

35
Q

what is the con of alumina porcelain?

A

it is opaque, need to build on more translucent shades

36
Q

what are glass ceramics?

A

fine grained polycrystalline materials obtained from a glass phase following a heat treatment

37
Q

pro of glass ceramic.

A

large number of fine crystals
= limit the development of flaws

38
Q

what is an example of a glass silicate? what is it made of?

A

IPS E.Max

  • 60% Lithium Disilicate
  • Lithium Orthophosphate
    layering material = fluoroapatite
39
Q

what are the 2 production routes in making glass ceramic materials?

A
  1. grind into fine power, melt, cast into mould
  2. crystallise, brings the tooth shapes
40
Q

what are the uses for glass ceramics?

A

veneers
inlays
onlays
posterior and anterior crown

41
Q

what ceramic has the best aesthetic?

A

glass

42
Q

instead of alumina, what can you use? why and how?

A

zirconia
- strong due to transformation toughening

43
Q

what is the property of zirconia when heating above 1000 degrees?

A

goes from monoclinic to tetragonal

  • opposite way when cooling down
44
Q

what does adding magnesium to Zirconia do? aka transformation toughening explained.

A
  • retains the tetragonal structure at low temps
  • energy from cracks is converted into converting tetragonal into monoclinic crystals
    = compressive forces = oppose tensile forces causing crack

= suppresses crack propagation

45
Q

in order, what’s the order of toughness for ceramics?

A
  • porcelain
  • glass ceramic
  • glass ceramic with alumina
  • zirconia high-tech

YR 3 - CSB (38 decks)

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