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Dental Materials > 10 - Cast Metal Restorations > Flashcards

10 - Cast Metal Restorations Flashcards

1
Q

What is the general process of fabricating a cast metal restoration

A

wax a pattern of the restoration on a die

invest the pattern to creat a mold space

cast the restoration

finish and polish the cast

cement the restoration intraorally

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2
Q

Becase of the complexity of this sequence, properties desriable for casting are governed as much by _____ as by _____

A

technique limitations, final intraoral service considerations

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3
Q

Cast metal alloys may be used to form either: ____ or _____

A

the entire restoration, or as a substructure and veneered with porcelain to create the tooth colored restoration

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4
Q

some of the names for cast metal alloys veneered to porcelain are

A

porcelain bonded to metal

ceramic bonded to metal

porcelain fused to metal

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5
Q

to successfully use with porcelain, metal alloy needs to have what?

A

relatively high melting point to tolerate the high firing temperatures of porcelain.

though, the melting temperature of resrotations that are all metal can be at any temperature that is convenient

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6
Q

what is a an essential characteristic of dental casting alloys

A

corrosion resistance

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7
Q

how can casting alloys be categorized in relation to corrosion resistance

A

1- mechanism of corrosion resistance

2- main elements in the composition that affect the corrosion resistance

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8
Q

corrosion resistance is achieved with either immune systems or passivating alloy systems.

Immune systems are divided into what two categories?

Passivating systems are divided into what three categories?

A

immune systems:

gold systems

gold substitute systems

Passivating systems: (NIC)

nickel chromium

cobalt chromium

iron chromium

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9
Q

_____ metal alloys are very resistant to corrosion.

these systems are based on what?

A

nobel metal alloys.

they are based on gold, platiunum, palladium, rhodium, iridium,ruthenium, or osmium

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10
Q

what are precious metal alloys

A

in the words of tony, alloys that contain precious metal… high economic value. traditionally include all the noble metals and silver

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11
Q

what are low gold alloys

A

3-50% weight gold or other noble metal elements

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12
Q

if less than ______ of the atoms in a gold alloy are corrosion resistant the overall corrosion resistance ________

A

half, decreases dramatically

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13
Q

what was the purpose of low gold alloys

how much gold is actually in these

A

produce lower cost alloys that still have some of the qualities of premium gold based alloys

the actual quantity of gold in these alloys is deceptively low

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14
Q

what are gold substitute alloys

A

precious metal alloys that don’t contain gold i.e. pd alloys

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15
Q

what are base metal alloys

A

based on active metallic elements that corrode but develop corrosion resistance via surface oxidation. it makes a tight adherent film that inhibits further corrsion.. like an aluminum canoe

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16
Q

an example of a base metal alloy is?

are the films tough?

A

Cr which makes a film of Cr2O3 on it’s surface.

the films are brittle and can rupture but if they do they reform immediately.

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17
Q

Ni and Co also oxidate, but ______ is principally responsible for the corrosion resistance

A

Cr2O3

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18
Q

Ti alloy is widely used in dentistry for what reasons?

A

It passivates (becomes unreacitve my forming a surface layer) by forming TiO2, it is biocompatible, it permits osseointigration with bone

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19
Q

cast restorations are constructed traditionally from what? why from this material?

A

gold alloys

becase they have excellent corrosion resistance

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20
Q

when were casting materials standardized?

how were dental gold casting alloys defined?

A

1930’s

they were defined by:

nobel metal concentration

physical properties

mechanical properties

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21
Q

The ADA classification system of gold alloys is what?

it was later switched to what?

A

A,B,C, gold alloys

later switched to I,II,III,IV

I,II,III correspond to the ABC but IV was added and is higher strength alloys

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22
Q

what is the nobel metal content (of which gold is the main one) of types 1,2,3,4?

A

I - 83%

II - 78%

III - 78%

IV - 75%

So as you go up, the nobel metal content goes down. this means higher strength but less burnishability… gold is soft

23
Q

What are each of the different alloy types used for? (I,II,III,IV)

which ones can be heat treated?

A

I - small inlays that do not involve significant occlusal loads

II - inlays and onlays

III - onlays and crowns

IV - crowns, bridges, removable partial dentures

I and II cannot be heat treated but the other two can.

24
Q

Gold is primarily responsible for producing ____ but is relatively ____ and requires other alloy elements to _____ the composition.

A

corrosion resistance

soft

harden

…. copper is the primary alloy element that increases the hardness of the alloy. it also makes the color less yellow and more orange.

25
Q

what is each alloy element used for?

A
26
Q

what has prompted the increased use of low gold, gold substitute, and base metal alloys?

A

the high cost of gold

27
Q

many crowns and fixed bridges are made of what?

the mechanical properties of this matieral make them difficult to what?

A

palladium based gold substitute alloys

mechanical properties make them hard to make inlays on onlays. you can’t burnish them, they are too hard. But, gradual improvement in low gold alloys have made them acceptable for selective use in these applications.

28
Q

many products containing about _____ % wieght of gold have acceptable tarnish resistance and adequate properties if too much burnishing is not required

A

50%

29
Q

why is a low melting range desirable?

why is moderately high density advantageous?

A

for simplified heating and casting procedures

becasue most dental alloys are normally cast by centrifugal force machines and high density material then fills all the nooks and cranny’s.

30
Q

why is high density alloy good

A

it helps the alloy quickly get into all the intricate details of the pattern within the mold before the cooling solidify’s the material. gold based alloys are good for this

31
Q

why is a low coefficient of thermal expansion good

A

it reduces shrinkage that occurs from the melting temperature down to room temp

32
Q

cooling produces____ so there must be some expansion somewhere else in the technique to compensate for it

A

shrinkage

33
Q

what alloys can be controlled more easily

A

ones that have low coefficients of thermal expansion and low melting temperatures

34
Q

the primary chemical property concern is what?

how is it achieved?

A

corrosion resistance

the entire alloy needs to be a single phase composition. two phase compositions are more prone to corrosion

35
Q

Of the alloy types I,II,III,IV, which are single phase

A

I,II,III are single phase. Type IV is two phase. The advantage of the two phase is that it is much harder… but that is at the expense of corrosion resistance

36
Q

what can produce unwanted phases and compromise mechanical properties and corrosion resistance?

A

contamination or improper casting of gold based alloys

37
Q

primary mechanical properties of interest are what?

A

high modulus of elasticity (stiffness) and a high elastic limit (hardness) to resist deformation during use

38
Q

it is harder to finish, polish, and burnish if what?

A

if the material has high resistance to plastic deformation (it is hard)… High values are not always good.

39
Q

during these processes it is important for the casting metal to?

A

have margins closely adapted to the die by minimal mechanical deformation. marginal gaps bigger than 0.1 mm should not be burnished, should re make the casting

40
Q

castings with ____ and ____ are easier to burnish

A

high percentage elongation and a low yield point (low hardness)

41
Q

what is OLYMPIA

A

i don’t know if these are important but i am including them for completeness

42
Q

what is williams academy gold

A

don’t think you have to know

43
Q

what is SIGN

A

don’t think you have to know

44
Q

what is MAESTRO

A

don’t think you have to know

45
Q

what is firmilay

A

don’t think you have to know

46
Q

what is sturicast

A

don’t think you have to know

47
Q

for longerm success what are 3 principle considerations?

A

close fit

corrosion resistance

retention

48
Q

gold based alloys are corrosion resistant for at least how long

A

ten years but if cemeneted restorations have a close fit and tooth prep is good they can be good up to 20-40 years

49
Q

retention and service life of cast restorations are produced by a number of things. what are they?

A

taper of the tooth prep

stress distribution design of the prep

cement type

surface roughness on internal aspects of restoration

micromechanical and chemical bonding

50
Q

under most circumstances, the restoration surface for gold based alloys is ______ to cement adhesion

A

not well suited. gold alloy surfaces do not wet well with cements and do not have the potential to be chemically bonded. But, if the internal surfaces are sand blasted, there are enough micromechanical irregularities to produce good luting (seal or joining)

51
Q

in a maryland bridge, retention of the casting depends on?

A

mirco mechanical spaces along the bonded surfaces of the enamel and casting

52
Q

the retentive surface of the casting is accomplished by what?

A

a two phase dental casting alloy. The metal surface to be bonded is relieved by chemical or electrolytic etching, then the relieved space is micro mechanically interlocked with composite cement onto etched tooth structure.

53
Q
A

Dental Materials (15 decks)

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