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dental materials > dental casting alloy > Flashcards

dental casting alloy Flashcards

1
Q

METAL RESTORATIONS IN DENTISTRY

A
  1. Direct filling (e.g., gold, amalgam)
  2. Casting (e.g., cast crowns, posts, inlays, etc.)
  3. Machining
     Prefabricated (e.g., prefabricated posts)
     CAD-CAM* (e.g., metal inlays, crowns, etc.)
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2
Q

CLASSIFICATION BASED ON YIELD STRENGTH AND PERCENT ELONGATION (ADA SP. 5 )

A

TYPE I (soft) - 83% Au = small inlays
TYPE II (medium) - 77% Au = inlays/onlays subjected to moderate stress
TYPE III (hard) - 75% Au = onlays, crowns, denture base, fpd, high stress
TYPE IV (extra hard)- 56% Au = subjected to very high stress, rpd frameworks denture base and clasps, long span fpd

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3
Q

CLASSIFICATION ACCORDING TO NOBILITY (ADA 1984)

A

I. High Noble (precious) ≥ 40% Au & ≥ 60% noble metals
II. Noble (semiprecious) ≥ 25% noble metals
III. Predominantly base metal < 25% noble metals
(nonprecious)

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4
Q

CLASSIFICATION ACCORDING TO THE THREE MAJOR ELEMENTS

A
  1. Gold-palladium-silver (Au-Pd-Ag)
  2. Palladium-silver-tin (Pd-Ag-Sn)
  3. Nickel-chromium-molybdenum (Ni-Cr-Mo)
  4. Cobalt-chromium-molybdenum (Co-Cr-Mo)
  5. Iron-nickel-chromium (Fe-Ni-Cr)
  6. Titanium-aluminum-vanadium (Ti-Al-V)
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5
Q

CLASSIFICATION ACCORDING TO THE NUMBER OF ALLOYS PRESENT

A
  1. Binary—two elements
  2. Ternary—three elements
  3. Quaternary (and so forth)—four elements
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6
Q

__ and titanium are the only metal
used in pure state for dental restoration
 Noblest of all dental metals
 Resist tarnish and corrosion inside oral cavity
 Inactive chemically
 Most ductile and most malleable
 Extremely soft but hardens after cold working
 Almost ideal restorative material in non aesthetic, low stress area

A

GOLD

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7
Q

Dental Gold Alloys (2)
Direct Filling Gold: 3 Categories

A

I. Direct Filling Gold
II. Cast Gold
1. Gold foil
2. Electrolytic precipitate gold
3. Granular (Powdered) gold

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8
Q

 Provided in sheets, which can also be transformed to other physical form like pellets, cylinders, ropes
 Standard No. 4 (4x4 in) gold foil weigh 4 grains (0.259 g)
 Platinized gold
 Noncohesive foil (ammonia-treated)

A
  1. Gold foil
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9
Q

 microcrystalline gold powder formed by electrolytic precipitation, which is sandwiched between sheets of gold foil and formed into strips.
 powder consists of dendritic crystals approximately 0.1 mm in length
 This form of gold can be cut to a desired size and is often preferred for its ease in building up the internal bulk of the restoration

A
  1. Electrolytic Precipitate (mat or sponge gold)
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10
Q

 prepared by chemical precipitation or atomization from molten gold
 precipitated powders are first mixed with a soft wax to form pellets
 wax-gold pellets are wrapped with foil

A
  1. Granular (Powdered) gold
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11
Q

PREPARATION OF DIRECT FILLING GOLD FOR RESTORATION

A
  1. Annealing, heat treatment, degassing, desorption
  2. Condensation/ Compaction
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12
Q

 Laboratory
 Inlays, onlays, crowns, all metal bridges, metal ceramic bridge, removable partial denture framework
 Superior durability and fracture resistance

A

II. Cast Gold

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13
Q

Provides tarnish and corrosion resistance and
has a desirable appearance. Also provides
ductility and malleability.

A

Gold

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14
Q

It is the principal hardener. It reduces the melting point and density of gold. If present in sufficient quantity, it gives the alloy a reddish color. It also helps to age harden gold alloys. In greater amounts, it reduces resistance to tarnish and corrosion of the gold alloy. Therefore, the maximum content should not exceed 16 percent.

A

Copper

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15
Q

It whitens the alloy, thus helping to counteract the reddish color of copper. It increases strength and hardness slightly. In large amount, however, it reduces tarnish resistance.

A

Silver

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16
Q

It increases strength and corrosion resistance. It also increases melting point and has a whitening effect on the alloy. It helps to reduce the grain size.

A

Platinum

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17
Q

It is similar to platinum in its effect. It hardens and whitens the alloy. It also raises the fusion temperature and provides tarnish resistance. It is less expensive than platinum, thus reducing the cost of the alloy.

A

Palladium

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18
Q

It acts as a scavenger for oxygen. Without zinc, the silver in the alloy causes absorption of oxygen during melting. Later during solidification, the oxygen is rejected producing gas porosities in the casting.

A

Zinc

19
Q

They help to harden ceramic gold-palladium alloys, iron being the most effective.

A

Indium, Tin and Iron

20
Q

It is added to compensate for the decreased CTE that results when the alloy is made silver free (the elimination of silver is done to reduce the tendency for green stain at the metal-porcelain margin).

A

Calcium

21
Q

They help to decrease the grain size. They are added in small quantities (about 100 to 150 ppm).

A

Iridium, Ruthenium, Rhenium

22
Q

two types of heat treatment of gold alloys

A
  1. Softening heat treatment (solution heat treatment)
  2. Hardening heat treatment (age hardening)
23
Q

 These alloys are also known as ‘stellite’ because of their shiny, star-like appearance. They are bright lustrous, hard, strong and possess nontarnishing qualities.
They possess high strength. Their excellent corrosion resistance especially at high temperatures, makes them useful for a number of applications.

A

Cobalt-chromium alloys

24
Q

Imparts hardness, strength and rigidity to the alloy. It has a high melting point.

A

Cobalt

25
Q

Its passivating effect ensures corrosion resistance. The __ content is directly proportional to tarnish and corrosion
resistance. It reduces the melting point. Along with other elements, it also acts in solid solution hardening. 30% is the upper limit
for attaining maximum mechanical properties.

A

Chromium

26
Q

Cobalt and __ are interchangeable. It decreases strength, hardness, MOE and fusion temperature. It increases ductility.

A

Nickel

27
Q

They are effective hardeners. __ is preferred as it reduces ductility to a lesser extent than tungsten. __ refines grain structure.

A

Molybdenum or Tungsten

28
Q

They are hardeners. In addition, b__ reduces fusion temperature and refines grain structure.

A

Iron, Copper and Beryllium

29
Q

Primarily oxide scavengers to prevent oxidation of other elements during melting. They are also hardeners.

A

Manganese and Silicon

30
Q

Deoxidizer and hardener but reduces ductility.

A

Boron

31
Q

__ content is most critical. Small amounts may have a pronounced effect on strength, hardness and ductility. __ forms carbides with the metallic constituents which is an important factor in
strengthening the alloy. However, excess __ increases brittleness. Thus, control of __content in the alloy is important.

A

Carbon

32
Q

can be defined as the act of forming an
object in a mold. The object formed is also referred to as __

A

Casting
a casting

33
Q

Casting Process (8)

A
  1. Wax pattern
  2. Spruing
  3. Casting ring lining
  4. Investment
  5. Wax elimination (burnout)
  6. Casting
  7. Deflasking
  8. Finishing and polishing
34
Q

an opening for the mold where
molten metal will pass

A

Sprue

35
Q

Earlier __liners were used. Its use has been discontinued due to health hazard from breathing its dust.

A

asbestos

36
Q

TYPES OF NONASBESTOS RING LINERS
USED ARE

A
  1. Fibrous ceramic aluminous silicate
  2. Cellulose (paper)
  3. Ceramic-cellulose combination
37
Q

Gypsum Based Products – Material for __

A

Investing

38
Q

The process of heating the invested pattern to melt the wax and flows out of the mold via the sprue (500 to 600oC).

A

Wax Burnout

39
Q

It is the process by which molten alloy is forced into the heated investment mold. (Technique sensitive)

A

Casting

40
Q

The investment is removed and the casting recovered. A pneumatic (compressed air driven) chisel may be used to remove the investment. Final bits of investment is removed by sandblasting.

A

. Deflasking

41
Q

the process by which particles of an
abrasive (usually aluminum oxide) is projected at highvelocity using compressed air in a continuous stream. The casting is held in a sandblasting machine to clean the remaining investment from its surface.

A

SANDBLASTING

42
Q

Surface oxides (e.g., black castings)
from the casting are removed by __ in 50%
hydrochloric acid. HCl is heated but not boiled
with the casting in it (done for gold alloys). __ is not a routine procedure and is performed only
when indicated.

A

PICKLING

43
Q

The sprue is sectioned off with a cutting disc. The casting is trimmed, shaped and smoothed with suitable burs or stones

A

TRIMMING

44
Q

DEFECTS IN CASTING (5)

A
  1. Distortion
  2. Surface roughness
  3. Porosity
  4. Incomplete casting
  5. Contaminated casting

dental materials (7 decks)

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