3. Spruing, Investing and Casting Porcelain Fused-to-Metal Alloys Flashcards by J L

Alloys for Metal-Ceramic restorations

• Noble alloys are heavily based on ____ or palladium
◦ You will find noble alloys that have very little gold, maybe 2%, but they are
still noble because they have a high content of ____

gold

palladium

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Lost wax casting sequence

• First we have a stone die and a wax pattern crown on top
• The next step is to attach a ____ pin to the crown
◦ We will talk later about what compositions you have for the sprue pin
• The sprue pin is attached to a sprue base
• Then, you attach a ____ ring to the sprue base
• You mix your investment and then pour it into ring
• Next, heat in oven
◦ Temp and time depend on what kind of casting you are doing
• After you heat investment, wax flows out and it is hollow
• Next step, put in casting machine
• Then you break out ____, cut off the sprue pin, polish, and deliver to pt

• Chart shows dimensional changes that occurred during the process
◦ Left shows when there is shrinkage, right is expansion
◦ The initial impression has a little ____
◦ There is some setting ____ when the die is poured
◦ Waxing: when it hardens, there is a little ____
‣ There is also some ____ that occurs in the early stages of heating
◦ All investment materials have a little setting ____
◦ Burnout = ____
◦ Whenever you solidify the molten alloy, there will be significant ____
◦ We are not looking for zero change, we are looking for a little bit of ____ (without this, it was fit very tightly)

sprue
copper
investment

shrinkage
expansion
shrinkage
expansion

expansion
expansion
shrinkage
expansion

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Considerations for Accurate Castings

Casting Formula
wax shrinkage + solidification shrinkage
= die stone \_\_\_\_ + wax \_\_\_\_ +
 investment setting \_\_\_\_ + hygroscopic \_\_\_\_ +
thermal \_\_\_\_ of investment

Tolerance of ± 0.05%

expansion
expansion
expansion
expansion
expansions

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Casting/solidification shrinkage
􏰈􏰈Gold/Noble metal alloys 1.4 - 1.6%
Base metal alloys 2.0 - 2.5%
􏰈􏰈Shrinkage of wax pattern
􏰈􏰈 ~0.3-0.8%

• Know that base metal alloys shrink more than ____ alloys
◦ Base metal alloys are cast at much ____ temperatures

gold/noble

higher

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Compensation for Solidification Shrinkage I

􏰈􏰈Master die - Dimensional changes
􏰉􏰉Setting Expansion
􏰊􏰊􏰊􏰊 0.1% Type ____ gypsum
􏰊􏰊 0.3% Type ____ gypsum 􏰉􏰉Wax pattern ____

Setting expansion from die stone ranges from 0.1% to 0.3% depending on type of gypsum used
There is also a slight wax expansion when we begin to heat the wax

IV
V
expansions

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Compensation for Solidification Shrinkage II

􏰈Investment Expansion
􏰉􏰉Setting and hygroscopic expansion
􏰊􏰊Setting expansion - ____%
􏰊􏰊􏰊􏰊Hygroscopic - ____%

􏰉􏰉Thermal expansion of investment
􏰊􏰊High heat Thermal Expansion ____%
􏰊􏰊Low heat Thermal Expansion ____% 􏰊􏰊(hygroscopic + wax expansion)

􏰉􏰉 Use of die spacer

• Hygroscopic expansion
◦ If we mix our investment and pour into casting ring, we can increase amount of expansion any immersing whole thing in water (this is
____ expansion of investment)
◦ Much more expansion than just letting it sit on the bench

• There will be thermal expansion of investment when we start to heat it
• There are different types of investment that accomplish their expansion primarily by thermal expansion
• The manufacturer is using these properties to balance the expansions
depending on the type of alloy being cast
◦ Instructions must be followed exactly

• The die spacer is painted on by technician before wax-up ◦ This is supposed to provide space for ____

4
2-2.2

1-1.6
0-0.6

hygroscopic

cement

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Considerations for Accurate Castings

􏰉􏰉Adequate ____ for solidification shrinkage & wax pattern shrinkage
􏰉􏰉Adherence to basic principles of ____
􏰉􏰉Appropriate ____ materials

• You must use the right type of investment for the casting you’re doing
◦ If you are casting gold inlays, you use ____ bonded investment ◦ But when you are casting PFM alloys, they are cast at much ____
temperatures than gold alloys
‣ Different investment is needed

compensation
casting
investment
gypsum
higher

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Techniques for Casting
􏰈􏰈\_\_\_\_ 
􏰈􏰈Investing
􏰈􏰈􏰈􏰈\_\_\_\_
&amp;
􏰈􏰈\_\_\_\_ Materials

spruing
casting
investment

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The Invested Wax Pattern

• First, we need to have an understanding of the invested wax pattern
◦ This is the wax pattern for an ____ or ____
• Within the casting ring would be the investment material
• We used to line the casting ring with asbestos (lol), we don’t do that anymore
• Notice that the wax pattern is below the top of the ____ by about 6mm
◦ The ____ is also below the top of the ring

inlay
onlay
casting ring
ring liner

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SPRUING
􏰈􏰈Purpose
􏰈􏰈􏰈􏰈 To provide a ____ in the set investment for wax ____, and for the molten ____ to fill the mold space.

channel
removal
metal

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Spruing
􏰈􏰈 Techniques
􏰉􏰉 Direct or Indirect

◦ ____ [left] are attached to individual units
◦ ____ [right] are attached to a connector bar

direct

indirect

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Spruing

􏰈􏰈Requirements
􏰉􏰉 Size
􏰉􏰉 Provide \_\_\_\_ 􏰉􏰉Direction
􏰊􏰊{Minimize \_\_\_\_}
􏰊􏰊 Location
􏰊􏰊 \_\_\_\_

􏰉􏰉 Materials

• Sprue size is important
◦ Want a sprue as thick as the ____ portion of the wax pattern
◦ When molten metal is flowing, there are no restrictions that will stop or
slow it down
• Provide a reservoir - same thing as a ____ used with indirect sprees
◦ Reservoir holds molten metal and allows it to flow and fill space freely
• Direction of flow
◦ Direct flow of metal into mold space minimizes ____
• Casts are done under force, therefore, it is important to make sure wax pattern
is well ____ the top of the casting ring

reservoir
turbulence
length

thickest
connector
turbulence
below

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Spruing
􏰈􏰈Requirements
􏰉􏰉 Custom
􏰉􏰉 ____ sprues

􏰉􏰉 Wax
􏰉􏰉 ____

prefabricated

plastic

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Direct Sprues
􏰈􏰈 Single and small multi- units
􏰈􏰈 Easy to use

􏰈􏰈 Constricted Sprues
􏰉􏰉 ____ density alloys)

􏰈􏰈 Flared Sprues
􏰉􏰉 ____ density alloys

• If you are casting ____ based alloys (high density), the point where the sprue is
attached must be flared (wider attachment point)
• When you are casting low-density alloys, use a constricted sprue
• We are not sure why/how constricted/flared spues work for low density and
high density alloys respectively
◦ No physical laws that explain why this works

low
high
gold

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Direct Sprues

􏰈􏰈Suck back ____ in a direct sprued casting

• Suck back porosity happens because the metal in the sprue ____ before the metal in the desired casting
◦ A part of the metal is sucked back into the sprue pin

porosity

froze

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Indirect Sprues
􏰈􏰈\_\_\_\_ melting/\_\_\_\_ density PFM alloys 
􏰈􏰈Exposed button will solidify \_\_\_\_ 
􏰈􏰈\_\_\_\_ serves as reservoir
􏰈􏰈\_\_\_\_ wax patterns against distortion
􏰈􏰈\_\_\_\_ flow of metal to all parts of the casting

• Typically used for ____ alloys, can also be used with noble
– base alloys are high melting
• This area is an exposed area, so the metal will solidify very quickly
◦ This is why the use of the runner bar is important for high melting alloys ◦ Indirect sprues help resist ____ more than direct
• FYI: he uses the terms “reservoir,” “runner bar,” and “connector bar” interchangeabl

high
low
rapidly
runner bar
stabilizes
equalizes
base
distortion

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Indirect Sprues

􏰈􏰈Place pattern in a ____ position to ensure that all parts of mold fill simultaneously

􏰈􏰈Facilitate orientation with ____ marker on crucible former

• Important to place pattern vertically in casting
◦ The runner bar is aligned ____ in casting ring, giving a more even
distribution of metal into mold space

vertical
wax
vertically

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Flow of Alloy During Casting

􏰈􏰈 Indirectly sprued PFM patterns
􏰈􏰈 Orientation mark aligns connector bar vertically in casting ring
􏰈􏰈 Flow of molten metal in connector raises ____ of surrounding investment

temp

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Flow of Alloy During Casting

􏰈􏰈 Heat around connector keeps it molten ____
􏰈􏰈 Orientation dots to position connector bar vertically in casting machine

• Some people describe the location of the runner bar as the heat center

longer

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VENTING
􏰈􏰈 Indications 
􏰉􏰉\_\_\_\_ castings
􏰉􏰉 High \_\_\_\_ and Basemetal alloys
􏰉􏰉\_\_\_\_ investments

􏰈􏰈Purpose
􏰉􏰉Allow rapid escape of ____ from mold cavity

• There is gas present in space that molten metal is flowing into
◦ If you are using a porous investment (____ bonded is very porous), gas
can disperse through porosity of material ‣ Venting is not needed with ____
◦ Force fed bonded and ____ bonded tend to be dense and they do not have a mechanism to disperse of gases
‣ If you are doing a large casting of high palladium and base metal alloys, and you are using ____ investments, you must provide another mechanism to dispose gases from the cavity

large
Pd
dense

gases

gypsum
gyupsum

silica
dense

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Vents
􏰈􏰈 Provide ____ for outflow of gases from dense investment
􏰈􏰈 Investment porosity
􏰈􏰈 Location of wax pattern

Study These Flashcards

channels

LINERS

􏰈􏰈Purpose
􏰉􏰉Provide room for investment ____

􏰈􏰈 Materials
􏰉􏰉 ____
􏰉􏰉organic cellulose material (paper)
􏰉􏰉____ fiber (Aluminum silicate) 􏰉􏰉ceramic/cellulose combination

Reason for liner: acts as a cushion allowing for expansion
• If liner is soaked in water, it provides water with ____ expansion

Study These Flashcards

expansion
asbestos
silica alumina
hygroscopic

LINERS

􏰈􏰈Keep asbestos substitutes short
􏰉􏰉____ mm short of ring
􏰊􏰊 to secure investment
􏰊􏰊to produce a more uniform expansion

􏰉􏰉Ring less casting

• Liner is kept short of top of ring
◦ This locks investment into the ring
• If too long, investment can be propelled out of the ring when heating starts
◦ ____ protocol
• Keeping it short and filling it with water produces a more uniform expansion of the investment
• Ring less casting
◦ Shape a piece of wax to look like a ring, place on sprue former and pour
investment into it
‣ Wax is removed when investment is set
‣ This removes any ____ to the expansion of the investment
• Can increase investment ____ dramatically

Study These Flashcards

3.0
safety
restriction
expansion

Investing

􏰈􏰈Apply ____ reducing agent
􏰈􏰈Weigh Wax pattern to determine weight of ____ needed

• Next step, we are going to invest the whole thing
◦ First, we apply a surface tension reducing agent
‣ A surfactant, allows investment to flow and helps prevent air ____ from forming
‣ ____ water can be used

Study These Flashcards

surface tension
alloy
bubbles
soap

INVESTING 􏰈􏰈Gypsum bonded investments: ____oC (1300oF) ``` 􏰈􏰈Investments used 􏰉􏰉____ and silicate investments 􏰉􏰉Mix under ____ to eliminate bubbles 􏰉􏰉____ investments preferred 􏰊􏰊 Dense 􏰊􏰊 High strength 􏰊􏰊 Smooth surface 􏰉􏰉Vents ``` • We will now talk about materials used for investing • Once you exceed 700 with gypsum, it begins to break down ◦ If it breaks down, the metal casting will get messed up ◦ We do not use gypsum bonded investment for PFM alloys • Phosphate and silicate are the best investments to use • Must mix under vacuum to eliminate air bubbles • [reads rest of slide]

700 phosphate vacuum thicker

Burnout of the Investment Mold 􏰈􏰈Mold ____ out during storage (store investment in a ____) 􏰈􏰈 slow heat from a ____ furnace 􏰉􏰉Rapid heat materials 􏰈􏰈ensure complete elimination of all ____ by long enough burn out • We have coated our wax pattern with surface tension reducing agent • Before the investment has completely set, you want to put it in oven ◦ Rapid heat materials can be heated rapidly without ____ • Very important to follow the manufacturers instructions because you want to make sure there is no residual wax in the investment ◦ Heat it for long enough to get rid of all ____ during the burnout process

``` dry humidor cold wax fracturing wax ```

Investment Burn-out 􏰈􏰈Phosphate Investment 􏰉􏰉􏰉􏰉Heat soak ____oC for 1 hour 􏰉􏰉Excessive heat soaking 􏰊􏰊____ of investment - ____ cast surface * The investment is a ceramic material * If you over-heat, it will sinter (fuse together) and form a very ____ surface

700-760 sintering rough

Crucibles 􏰈􏰈____ -alumina 􏰈􏰈 Quartz 􏰈􏰈____ coded for different alloys • Gold pellets are heated in a crucible • Molten metal flows through hole in crucible and into the casting ring • Materials used for crucibles: ____, quartz ◦ Do not cross ____! Don't used the same crucible with different alloys

zirconia color zirconia-alumina contaminate

MELTING ``` 􏰈􏰈Melting/Casting Temperature 􏰉􏰉____oC higher 􏰉􏰉􏰉􏰉 Ceramic alloys around ____oC 􏰈􏰈Phosphate and silicate investments 􏰈􏰈Evaporation of ____ melting constituents during melting 􏰉􏰉Reusing buttons ``` • Alloys melt over a ____ of temperatures • Want to heat alloy to above the solidus temperature ◦ Typically 100-200 degrees higher than liquids temperature to be sure everything is melted • There is a metal button cast at the sprue base ◦ This has been heated to the same temp as the ____ ◦ For ____ metal alloys, you cannot reuse this button because the composition has changed too much ◦ For ____ metal alloys, they can be reused

100-200 1300 ``` low range casting alloy base noble ```

Heat Sources for Melting Alloys 􏰈􏰈____ Melting 􏰈􏰈____ Heating 􏰈􏰈____ Melting

Torch Electrical Arc

Torch Melting 􏰈􏰈 Gas/air Blow pipe for melting alloys 􏰈􏰈 Zones of melting flame ``` 􏰈􏰈 Gas (propane)/oxygen (____0oC) 􏰉􏰉 Liable to ____ 􏰉􏰉 ____ of alloy 􏰉􏰉 Excessive oxidation of ____ metals ``` • The mixing zone is very ____ ◦ Oxygen and gas mixing together • Next zone is the combustion zone, looks ____ • Next zone is reducing zone, ____ ◦ This is the ____ you want to put on the metal to get the most amount of heat • Need a hot flame when casting PFMs ◦ Typically propane/oxygen mixtures are used • If you overheat, you change properties of the alloy

1800-2500 overheating evaporation base dark yellowish blueish zone

CASTING ``` 􏰈􏰈Centrifugal casting 􏰉􏰉Centrifugal force proportional to 􏰊􏰊 ____ of casting arm 􏰊􏰊 ____ of metal 􏰊􏰊 Extra turns for ____ density alloys ``` 􏰉􏰉 No flux for ____ & ____ metals 􏰊􏰊 may alter compositions and affect bond strength • Centrifugal force is proportional to the ridges of the casting arm • High density alloys will flow easily into the casting space • Low density alloys require a faster centrifuge to increase the force • Flux helps to remove the oxides on the surface of noble/gold based alloys ◦ Flux will contaminate alloy if using silver-palladium and base metal alloys ‣ Reduces bond strength to porcelain

``` radius mass low Ag-Pd base ```

Vacuum/pressure Casting ``` 􏰈􏰈 Melt alloy to prescribed ____ Place preheated nvestment over crucible 􏰉􏰉 Apply ____ 􏰉􏰉 Turn casting chamber 180o, apply ____ ``` • Another method of casting • Once metal is melted, the chamber is flipped [bottom pic] and ____ pulls the molten metal into the cast ◦ You then introduce high pressure gas so the mold space is filled adequately

temperature vacuum pressure gravity

Cleaning PFM Alloys - sandblast PFM alloys - gold based alloys are pickled in ____ • Once you have your casting and it is cool, you break it out of the investment • Gold based alloys cleaned in a pickleing solution ◦ Typically diluted ____ ◦ For ____ based alloys ONLY

acid sulfuric acid gold

Casting Defects 􏰈􏰈 Distortion - ____ pattern 􏰈􏰈 Fins - cracked ____ Surface roughness - grain ____ of investment 􏰈􏰈 Bubbles - excess ____, air • Problems that can occur during casting process • If your sprue wax pattern is not ____ and rigidly attached, you can get distortion ◦ Any deviation of wax pattern from its position in the investment, you can get distortion • Heated too quickly = cracks in investment ◦ You get fins on your casting where mental flowed into cracks • Over heated ceramic can fuse together and give a rough casting • Bubbles on surface of casting

wax investment size debubblizer stable

Casting Defects 􏰈􏰈Underheating - 􏰉􏰉____ casting 􏰉􏰉____ coating 􏰈􏰈Prolonged heating 􏰉􏰉____ of investment 􏰈􏰈Foreign bodies 􏰈􏰈Porosity • Carbon coating can occur with under and over heating depending on type of investment being used ◦ Some investments contain carbon • Prolonged heating will result in a rough surface • Must work in clean environment to avoid ____ in the investment

incomplete carbon disintegration foreign bodies

Casting Defects 􏰈􏰈Adequate Reservoir 􏰉􏰉No ____ cast 􏰈􏰈Inadequate reservoir 􏰉􏰉____ is cast 􏰉􏰉Inadequate ____ • The connector bar was not adequate enough and we have incomplete casting • Adequate reservoir, there is no button cast, so most of the metal has flowed into the space to give us a good casting

button button casting

Poor Alloy Castability 􏰈􏰈Incomplete / rounded margins due to poor ____ castability • If your alloy doesn't flow well when it is heated, you can have rounded margins • The base metal alloys contain Beryllium ◦ Beryllium is present to improve ____ of metal and to avoid ____ edges in casting

alloy flow rounded

Casting Defects Nodule: ____ trap during investing Inadequate ____ during mixing Prolonged ____ Shrink spot porosity Long thin sprue bulky ____ ____ button * If you don't use a vacuum, bubbles can form * Prolonged vibration during investing can also produce bubbles * Inadequate sprueing can result in a ____ spot porosity in your casting

``` air vacuum vibration attachment small shrink ```

* Impurities a.k.a. foreign bodies. Work in a ____ environment to avoid this * Fins are formed when there are ____ in the investment * Blunt margins = poor ____ * Carbon can occur from both excessive ____ and under ____

``` clean cracks flow heating heating ```

INVESTMENT MATERIALS FOR METAL-CERAMIC RESTORATIONS 􏰈􏰈____ Bonded Investments 􏰈􏰈____ bonded investments * We will end by mentioning a few properties of the 2 types of investment materials used in PFM alloys * Silicate is used for much ____ temperature alloys than phosphate bonded

phosphate silicate higher

Phosphate bonded investments 􏰈􏰈Two types 􏰉􏰉Carbon Containing - ____ of divesting 􏰊􏰊Carbon contamination of alloy makes alloy ____ 􏰉􏰉____ containing • 2 types of phosphate bonded ◦ Carbon containing ‣ When heating, the loss of carbon makes it easy to break the casting out of the investment (divesting) ◦ For some alloys, especially base metal alloys, carbon is going to make the alloy brittle ◦ Non carbon containing are typically used for ____ metal alloys

ease brittle non-carbon base

Phosphate Bonded Investments Composition 􏰈􏰈Binder 􏰉􏰉Mono ____ 8-12% 􏰉􏰉____ 8-10% 􏰈􏰈Refractory 􏰉􏰉____ + Cristobalite 30-50% 􏰉􏰉____ only (high temperature ____) 􏰈􏰈Setting agent/Reaction 􏰉􏰉____ 􏰊􏰊 Binder + setting agent --> ____ strength Setting ____ • The binder here is ammonium phosphate and magnesium oxide mixed together • There is a refractory, quartz and cristobalite ◦ The role of the refractory is to provide for thermal ____ ‣ When we heat our investment, the refractory component of the investment (it is either quartz or cristobalite) • The setting agent is a colloidal silica that reacts with the ammonium phosphate the magnesium oxide • The binder and the setting agent react to give us an early green strength and some setting expansion

``` ammonium phosphate magnesium oxide quartz quartz burnout ``` colloidal silica green expansion burnout

Setting Expansion 􏰈􏰈Usual silica sol:water ratio = ____ 􏰈􏰈More silica sol and less water = more ____ 􏰈􏰈Less silica sol and more water = less ____ * If you want to increase the expansion, increase the amount of silica present * To decrease, decrease amount of silica

3:1 expansion expansion

Expansion 􏰈􏰈____ expansion 􏰈􏰈____ expansion 􏰈􏰈􏰈􏰈Thermal expansion 􏰉􏰉Inversion of cristobalite and ____ α ----> ß (200-270oC) 􏰉􏰉Max burnout temp. - ____oC • The main way of obtaining our investment expansion is by thermal ____ • Cristobalite and quartz are different forms of ____ (SiO2) ◦ There is a transformation from alpha form to ____ form, creating an increase in ____

``` setting hygroscopic quartz 900-1000 expansion silica beta expansion ```

Thermal expansion of quartz and crystobalite 􏰈􏰈Crystobalite 􏰉􏰉Max expansion above ____oC 􏰈􏰈Quartz 􏰉􏰉Max expansion above ____oC • This graph shows the difference in thermal expansion between crystobalite and quartz ◦ Crystobalite reaches maximum expansion at ____ temp than quartz ‣ If you are using a high melting alloy, you will probably have ____ present providing the maximum expansion • IT IS IMPORTANT TO KNOW THAT CRYSTOBALITE AND QUARTZ ARE BOTH ____ FORMS OF SILICA (he emphasized this)

``` 400 600 lower quartz allotropic ```

Mold expansion • The main method of obtaining expansion is by ____ EXPANSION

thermal

Handling of Phosphate Bonded Investments 􏰈􏰈Poor surface ____ 􏰈􏰈Greater likelihood of trapping ____ 􏰈􏰈Use ____ or open investing 􏰈􏰈Allow investment to set in ____ pot 􏰈􏰈coat surface of wax pattern with ____ before pouring investment into ring • When we are applying phosphate bonded investments to our wax, we need wettability, important to use ____ reducing agent ◦ Don't overuse (could cause bubble

wettability bubbles vacuum pressure investment surface tension

Silicate bonded investments 􏰈􏰈Binder 􏰉􏰉 ____ 􏰈􏰈􏰈􏰈 Refractory 􏰉􏰉____ only (Coarse grained) 􏰈􏰈Setting agent 􏰉􏰉____- promotes gelation setting reaction- polymerization of ____ • Silicate investment binder is a ethylorthosilicate • Remember Silicate bonded investments are much ____ temp investments ◦ They only have quartz for thermal expansion • The setting agent is magnesium oxide ◦ This reacts with ethylorthosilicate to provide a ____ ‣ The gel is basically polymerized silicic acid when the reaction is completed

ethylorthosilicate quartz magnesium oxide silicic acid higher gel

Expansion 􏰈􏰈 ____ expansion only 􏰉􏰉 α Quartz---> ß Quartz 􏰈􏰈 Max burnout temp. ____oC • The main method of expansion for silicate bonded investment is ____ expansion (He said this many times) ◦ Alpha quartz to beta quartz

thermal 1100-1300 thermal

Electrical Heating 􏰈􏰈􏰈􏰈____ heating 􏰈􏰈____ heating 􏰈􏰈____ arc Electrical heating systems 􏰈􏰈Resistance heating with 􏰈􏰈____ casting unit

resistance induction electric centrifugal

Electrical heating systems Induction Heating 􏰈􏰈 ____ cooled induction coil 􏰈􏰈 ____ crucible positioned within induction coils

water | vertical

3. Spruing, Investing and Casting Porcelain Fused-to-Metal Alloys Flashcards

(52 cards)