DENTAL CASTING PROCEDURESDENTAL CASTING PROCEDURES

• HISTORY

• WAX PATTERN

• INLAY WAX

• SPRUE FORMER

• INVESTMENTS

• DIE MATERIALS

• WAX ELIMINATION

DEFINITIONDEFINITION

Provides a metallic replacement for the missing tooth structure with as much of precision as possible.

HISTORYHISTORY

1897 D. Phil Brook

1907 William Taggart

Lane - compensation for shrinkage

1932 Schen - hygroscopic expansion

1942 Sonder - lining of casting ring

ADVANTAGES ADVANTAGES • Strength

• Reproduction of details

• Less corrosion & tarnish

• Less internal tarnish

• Finishing & polishing outside oral cavity

DISADVANTAGESDISADVANTAGES

Extensive tooth preparation

Microleakage

Galvanism

Multiple visits

Technique sensitivity

INDICATIONSINDICATIONS Extensive tooth involvement

Contact & contour replacement

Occlusal correction

Restoration of endo treated tooth

Partially subgingival restorations

CONTRAINDICATIONSCONTRAINDICATIONS

Young teeth with large pulp chamber

Caries & plaque indices high

Severe occlusal disharmony

Dissimilar metallic restorations

DENTAL WAXES

PATTERN PROCESSING IMPRESSION

INLAY BOXING CORRECTIVE CASTING UTILITY BITE BASE PLATE STICKY

DENTAL WAXES

PATTERN PROCESSING IMPRESSION

INLAY BOXING CORRECTIVE CASTING UTILITY BITE BASE PLATE STICKY

WAXESWAXES

MineralNatural waxes Plant Insect

Polyethylene PolyoxyethyleneSynthetic Halogenated carbon wax Hydrogenated wax Wax ester

INLAY CASTING WAXINLAY CASTING WAX

Inlay wax is a specialized dental wax that can be applied to dies to form direct or indirect patterns for the lost wax technique used for casting metal or hot pressing of ceramics.

Generally produced in deep blue, green or purple color.

COMPOSITION OF INLAY WAXCOMPOSITION OF INLAY WAX

Paraffin-60%

Carnauba-20%

Ceresin-5%

Beeswax-5%

Natural resins(gum dammer)-less than 1%

Organic fillers- added to avoid excessive shrinkage,expansion due to temp change

Microcrystalline wax- In minute amount.

Candelilla

Coloring agents

PARAFFIN WAX (MINERAL PARAFFIN WAX (MINERAL WAX)WAX)

Generally the main ingredient of inlay waxes.

Obtained from high boiling fractions of petroleum(methane

series)

Mixture of hydrocarbons

Melting range 40-71o C. increases with increasing molecular wt.

Paraffin waxes have less than 0.5% oil.

Presence of oil lowers melting temp.

Likely to flake when trimmed.

Does not present smooth, glossy surface

Consequently other waxes and natural resins

are added.

CARNAUBA WAX (PLANT WAX)CARNAUBA WAX (PLANT WAX)

• Derived from tropical palms• It is quite hard, melting range 84-910C• Combined with paraffin to-

Decrease flow at mouth temp

increase the hardness• It contributes to glossiness of the wax surface

(Addition of 10 % carnauba wax to paraffin wax with a melting range of 200C will increase the melting range to 460C.)

NATURAL RESIN (GUM DAMMER)NATURAL RESIN (GUM DAMMER)

• Less than 1%

• Added to paraffin to improve its smoothness in molding

• It renders it more resistant to cracking and flaking

• Increases the toughness of the wax and enhances the smoothness and

lusture of the wax.

• Similar to paraffin waxes, but obtained from heavier oil fractions.• It has a higher melting range 60-910C • It is tougher and more flexible than paraffin• It has less volumetric shrinkage during solidification than paraffin.

Decreases flow at moth temp.

Decreases brittleness of the wax at mouth temp.

CANDELILLA WAX (PLANT WAX)CANDELILLA WAX (PLANT WAX)

• Same qualities as carnauba wax

• Added to paraffin to partially or entirely replace carnauba wax.

• Its melting point is lower, and it is not as hard as carnauba wax.

CLASSIFICATION OF INLAY WAXESCLASSIFICATION OF INLAY WAXES

According to ADA SPECIFICATION 4

TYPE 1 -medium wax used for direct wax pattern

TYPE 2 - soft wax used for indirected wax pattern

Cervical wax-Cervical wax- for the cervical area, no shrinkage , a for the cervical area, no shrinkage , aVery accurate fit will be obtained, melting point 74Very accurate fit will be obtained, melting point 7400CC

Special wax for electrical wax heating unit(vario therm),dark blue-hard and light blue Special wax for electrical wax heating unit(vario therm),dark blue-hard and light blue soft are for modelling,trimming and dipping application, lilac-medium hard , red stresssoft are for modelling,trimming and dipping application, lilac-medium hard , red stressFree for cervical margins, green-hard for trimming. Dip application yellow wax caps ofFree for cervical margins, green-hard for trimming. Dip application yellow wax caps ofUniform strength.Uniform strength.

TYPESTYPES

Flow

Hard

Regular/medium

Soft

IDEAL PROPERTIESIDEAL PROPERTIES

Should soften uniformly & show colour contrast

Should allow smooth carving without flaking

Should be rigid and stable after taking the pattern

Should not leave a residue more than 0.1 % at 500 ° C

FLOW

THERMAL PROPERTIES

WAX DISTORTION /WARPAGE OF WAX PATTERN

• MOST SERIOUS PROBLEM

• THERMAL CHANGES & RELAXATION OF STRESSES

• ELASTIC MEMORY

Distortion results from

-thermal changes -relaxation of stresses (on cooling) -occluded air -molding -carving -removal and the time and temp of storage

MANIPULATION OF INLAY WAX

• Dry heat is preferred to the use of water bath (54-600C)• For type I (direct technique), it is softened over a flame until it becomes

shiny.• It is kneaded, shaped and pressed in the prepared cavity.• Pressure is applied by finger or pt biting on it.• It is cooled gradually, before taking out.

For fabricating indirect pattern (type II) die should be lubricated, preferably with a lubricant, containing a wetting agent.Excess must be avoided .Melted wax is added in layers with a spatula or waxing instrument or may be painted on with a brush.Wax is then carved to proper contour.A silk or fine cloth may be used, for final polishing.

WAX PATTERNWAX PATTERN

Without matrix band

With matrix band

Indication

• In easy accessible areas• when cavity is small with minimal proximal extension.• when cavity walls are flat ,line angles definite

Advantages

• The pattern is carved on tooth and not on model • Little laboratory work compared to indirect tech

Disadvantages

• Great skill and patience is required to carve pattern in mouth• When it is carved in indirect vision it is difficult and fatigue• Discrepancies of the pattern at the gingival margin are difficult to detect

until the pattern has been carved and withdrawn• as most of the adjustment and polishing is do on the tooth valuable chair

side time is lost • If the casting fails ,the patient has to be recalled

INDICATIONS

Inaccessible areas

Mostly full crowns and fixed partial dentures

ADVANTAGES

Easily made in inaccessible areas

Less strain to patients and dental surgeon

Newer impression materials give finer details

Direct vision is used in pattern fabrication All margins better finished and burnished before cementation Inlay is made on articulated models – better occlusal restoration Polishing is done outside the oral cavity If casting failure occurs, patient recall not necessary

DISADVANTAGES

Impression may be distorted Dentist depend on technician

WAX PATTERNWAX PATTERN

SPRUE FORMERSPRUE FORMER

Channel for flow of molten metal in to mold space

Size between 6 & 18 gauge ( 4 . 1 to 2 mm diameter )

Length 6 mm from the open end of the ring ( 1 / 4 inch )

Attachment 45 degrees and flared

WAXING UPWAXING UP

The end of the sprue that is attached to the wax patternshould be waxed out to form a gentle taper

CRUCIBLE FORMER CRUCIBLE FORMER

Attached to the sprue Made of plastic, wax or ceramic Should not be too conical to allow very rapid flow of the molten metal

Velocity of molten metal depends on:• Density of molten metal• Speed of evacuation of gases • Viscosity of molten metal• Length of sprue • Flare of the sprue

INVESTMENTS FOR CASTING INVESTMENTS FOR CASTING

INVESTMENT a ceramic material that is suitable for forming a mould into which a metal or alloy can be cast Procedure INVESTING

¶ Strong to bear casting pressure

¶ Withstand high temperature

¶ Should expand enough

¶ Porous enough to allow venting of gases

¶ Have a smooth surface finish

¶ Should easily break away after casting

¶ Manipulation should be easy

¶ Should be in expensive

Refractory material - Withstands heat - Silica

Binder Ca SO 4 Alfa hemi hydrate , PO 4 and Ethyl Silicates also serve the purpose .

Additives NaCl , Boric Acid , KSO 4, Graphite , Cu powder , Mg Oxide and coloring agents.

COMPOSITIONCOMPOSITION

Phosphate bonded High melting Metal ceramics

Gypsum bonded Low melting Gold alloys

Silica bonded High melting Base metal casting

GYPSUM BONDED INVESTMENTGYPSUM BONDED INVESTMENT

Silica Modifiers: Colouring agents Reducing agents Boric acid Sodium chloride

BinderAlfa hemihydrate of gypsum – 25 – 45 %200 – 400 ° C - shrinksClose to 700 ° C - expands Above 700 ° C - decomposition

QUARTZQUARTZ

Two stable polymeric forms

Alfa – low temp.

Beta – high temp.

Transition temperature 573 ° C ( Alfa form to Beta form )Expansion 1.4 % at apprly. 573 ° C

CRYSTOBOLITECRYSTOBOLITE

Uniform till 200° C after which a sudden expansion from 0.5 –1.2 %Above 250° C becomes uniform – 1.6 %Transition temp. 220° C

ADA Spec no 2 ----investment for dental gold alloys.

TYPE-1TYPE-2TYPE-3

NORMAL SETTING EXPANSION

HYGROSCOPIC EXPANSION HYGROSCOPIC EXPANSION

A lenier expansion of the investment when It sets in contact with water.

æ Casting ring in water bath

æ Controlled water added technique

æ Wet liner

THERMAL EXPANSION

PHOSPHATE BONDED INVESTMENT

ETHYL SILICATE BONDED INVESTMENT

DEFINITION - A die is working replica of a single tooth, several teeth.

MATERIALS USED FOR FABRICATION OF DIESMATERIALS USED FOR FABRICATION OF DIES

GYPSUM METAL POLYMER CEMENTS CERAMIC

1. It should be accurate

2. It should be dimensionally stable under normal conditions of use and

storage

3. Setting expansion and contraction, variations in response to change in

temperature need to be minimum

4.It should reproduce the fine details such as prepared and unprepared tooth satisfactorily .

5.It should be strong and durable and be able to withstand the subsequent manipulative procedures without abrasion or fracture.

6. They should withstand the carving and finishing procedures

7. The color should contrast that of the wax to ease the manipulation

8. Economical

9. Easy to use

GYPSUM

ELECTROFORMED DIESELECTROFORMED DIES

Silver plating bath Copper plating bath

Ag Cyanide 36 gms Cu SO4 225 - 250K Cyanide 60 Con H2 SO4 75 mlK CO3 40 Phenol 10 mlDistilled water Ethyl alcohol 25 -- 50 ml

A reservoir is added to prevent "LOCALISED SHRINKAGE POROSITY"

The reservoir, should be larger Wax is added around the sprue former 1-

2mm from

The pattern in order to create the reservoir.

CASTING RING

• usually metal• - Use of paper or plastic casting ring.• - Casting rings are available in different sizes.

• Selection of the casting ring• For hygroscopic technique-Rubber ring

Thermal expansion - Metal ring

Non corrodable & hard

Thermal expansion similar to that of the investment

Should also be compatible with liner , investment the liner

Length 38 mm Diameter 29 mm

INVESTED CASTING RINGINVESTED CASTING RING

CASTING RING LINERCASTING RING LINER ABESTOS LINER, FLEXIBLE RUBBERLINER, ALUMINO SILICATE LINER ,CELLULOSE

PAPER LINER

Semi hygroscopic expansion

Two layers- greater expansion

Shouldn’t be les than 1 mm

Length - Controversy

3.25 mm short of the end of the ring – more uniform expansion

RING WITH PATTERNRING WITH PATTERN

INVESTINGINVESTING

Process of covering or enveloping fully or part of a wax pattern with an investment material.

Objectives:

Make surface of mould smooth Allow venting of gas Compensation of shrinkage

INVESTINGINVESTING

Hand investing

Mixing 1 minute

Vibrator 30 seconds

Vacuum investing

INVESTINGINVESTING

BURNOUT PROCEDUREBURNOUT PROCEDURE

It’s the elimination of the wax pattern from the mold of set investment material.

Should be started after the investment has set (preferably 45 – 60 mins) but ideally before 60 mins.

If burnout is to be delayed the invested pattern should be placed in a humidor at 100% humidity

Procedure:

The crucible former and any metal sprue former are carefully removed.

Any debris from the ingate area is cleaned with a brush.

Invested rings are placed in a room temperature furnace and heated to a prescribed temperature.

TECHNIQUES

Gypsum bonded invst. Phosphate Bonded invst.

Gypsum bonded investment

Hygroscopic low heat technique High heat thermal expansion technique

@500 @700

(Type II gypsum bonded (Type I gypsum bonded investment

Investment material) material)

Phosphate Bonded investment

@ 700-1300 C, depending on the alloy selected

HYGROSCOPIC LOW HEAT TECHNIQUEHYGROSCOPIC LOW HEAT TECHNIQUE

With type II gypsum bonded investment

Disadvantages High chances of back pressure porosity in this technique because retained fine carbon may

block the pores in the investment causing reduced venting

Also, the investments used for this technique are denser.

Advantages Advantages Less investment degradationLess investment degradationsmoother castings.smoother castings.Molds can be directly placed in the 500Molds can be directly placed in the 500C furnace.C furnace.

1. Warm water bath

2. Hygroscopic expansion [ 1.2 %– 2.2% ]

3. Thermal expansion [ 0% - .6% ]

Mold should remain in the furnace for 60 min

MODIFICATIONS NEWER NOBLE ALLOYS

1. water bath temp to 40C.

2. the burnout temp range 600C - 650C

3. Two layers of liner

to compensate for increased expansion requirement of noble alloys

CONTROLLED WATER ADDED TECHNIQUE

Hygroscopic expansion is directly proportional to the amount of water added

Soft flexible rubber ring is used

Specified amount water added according to requirment

Rarely used

HIGH – HEAT THERMAL EXPANSION HIGH – HEAT THERMAL EXPANSION TECHNIQUE TECHNIQUE

Type I gypsum bonded investments

Compensation expansion

1. Heating the gypsum investment on setting(1 – 1.6% )2. Water entering from the wet liner (hygroscopic expansion)3 Expansion of wax pattrern

Require use of metal ring for protection Moulds placed in furnace @ room temp.

Slowly heated to 650C - 700C in 60 mins.

Held for 15 – 30 mins at the upper temperature.

Air pressure casting

Centrifugal casting

Vacum casting

[ ceramic casting with piston plunger ]

CASTING MACHINESCASTING MACHINES

Old method of casting

Pressure 10 to 15 p s i

Solidification of the metal in 5 seconds

AIR PRESSURE CASTING AIR PRESSURE CASTING

Spring loaded Pressure 30 to 40 p s I

Spring is 5 winds or 3 winds

11 gauge sprue 5 winds 0 . 38 minute 3 winds 0 . 4614 gauge 5 0 . 44 3 0 . 5417 gauge 5 0 . 51 3 0 . 67

CENTRIFUGAL CASTINGCENTRIFUGAL CASTING

C F is directly proportional to the square of the speed in revolutions per second

C F varies directly with the radius of the path

C F is directly proportional to the weight of the metal

[ C F Centrifugal Force ]

CENTRIFUGAL CASTINGCENTRIFUGAL CASTING

INDUCTION CASTINGINDUCTION CASTING

CASTING FLAMECASTING FLAME

BURNERS & FLAMES

Blow torch with oxygen gas and multi orifice tip Torch flame should not be more than 40 mm

Flame has 4 zonescool mixing zone ( combustion free zone )partial combustion ( green )reducing zone ( dimly blue , hottest )oxidizing zone less heat

combustion occurs with air metals can form oxides and contaminate metal

Borax

Reducing Fluxes - Borax + Carbon

Fluxes dissolve the oxides formed during melting of alloy

FLUXESFLUXES

MELTING OF ALLOYMELTING OF ALLOY

MELTED ALLOY

Density of cast metal

Porosity of investment

Length & diameter of sprue

Angulation of sprue

No of sprue

MOLD SPACE FILLINGMOLD SPACE FILLING

1. Blow torch a, Natural Gas b, Natural Gas and oxygen c, Oxyacetylene & oxygen mixture

2. Induction Energy

MELTING OF ALLOYMELTING OF ALLOY

RECOVERY OF CASTINGRECOVERY OF CASTING

• Leave in the casting machine for 12 min.• Quench in water

• Improves softness and ductility of the alloy• Better finish

HEAT SOFTENING

Pickling Hydrochloric acid Produces lot of fumes corrosion

Sulphuric acid + Potassium dichromate preferable

CASTING FAULTSCASTING FAULTS

A casting may be:

1. Dimensionally inaccurate

2. Have a rough surface and/or fins

3. Be porous, contaminated or incomplete

(The Clinical Handling of Dental Materials. BGN Smith, PS Wright, D Brown)

DISTORTION

SURFACE ROUGHNESS AND IRREGULARITIES

POROSITIES

INCOMPLETE CASTING

DEFECTS OF CASTING DEFECTS OF CASTING

SURFACE CRACKSSURFACE CRACKS

Wax pattern

T E , S E , H E of investments

Improper handling of wax pattern

Use of wax not conforming to ADAS # 4

DISTORTION DISTORTION

Finely spaced irregularities having a definite pattern

Irregularities without definite pattern - Ridges & veins

Due to improper wetting, trapping of air bubble

Overheating of the alloy

SURFACE ROUGHNESSSURFACE ROUGHNESS

Inadequate sprue

Mold too cold

Ingate expected

Insufficient pressure to force the molten metal

Inadequate quantity of molten metal

Alloy not fully melted

INCOMPLETE CASTINGINCOMPLETE CASTING

Incomplete burn out resulting in Carbon residue in mold space

Proper burn out can reduce the effect

Insufficient sprue diameter & length causes freezing of metal ahead of the mold

ROUNDED MARGINSROUNDED MARGINS

Sulphur contamination heat over 700 ° c

Copper contamination if steel tongs are used during pickling

Mercury contamination if amalgam die is used

DISCOLORED CASTINGDISCOLORED CASTING

Locallized shrinkage porosity

Hot spot

Reservoir, flaring of sprue , & reducing mold temperature by 30 to 50 degrees can prevent this type of porosity

POROSITIES IN CASTINGS POROSITIES IN CASTINGS

Micro porosities Premature solidification , low casting temperature

Gas inclusion Entrapment of air during solidification ( spherical voids ) Can also absorb oxygen & hydrogen ( poorly adjusted flame )

Back pressure porosity Improper venting

Sub surface porosity Simultaneous nucleation of solid grains and gas bubbles

POROSITIES CONTDPOROSITIES CONTD

Ceresin Product of petroleum refining or lignite refining Increases the M.P. of paraffin

Paraffin Hydrocarbon , MP 40 to 70° C Flakes easily 11 to 15 % contraction

Micro crystalline wax 61 to 90° C tougher more flexible than paraffin

Ozokerite USA & Western Europe

Montan From lignites . 72 - 92 , Hard but brittle Easily blend with any other wax

Ceresin - St. & br. Chain Petroleum & lignite refining product Increases M.P. of paraffin

Montan wax – L. refining 72 – 92 °C Hard, brittle & lustrous Blends with any wax

Ozokerite - only in Europe & USA M.P. 65°C

Similar to high mol. Wt. Paraffin

Gums – g. tragacanth & g. arabic

Fats – esters of fatty acids with glycerol

Tasteless, colourless , odorless & clear

PLANT WAXESPLANT WAXES

Carnauba wax – Hard, brittle M.P. 84 - 91 °C Reduces flaking

Candelilla wax - Hardens & reduces flaking of paraffin M. P. 68 - 75°C

Japan wax - Fat + glycerides of palmitic & stearic acid Tough, malleable & sticky M.P. 51 °C

Cocoa butter - Fat, glycerides, pal. & stearic, oleic & lauric acids

INSECT & ANIMAL WAXESINSECT & ANIMAL WAXES

Bees wax – Esters of myricyl palmitate & hydrocarbons M. P. 63 – 70 °C Brittle at room temp., plastic at body temp. Modifies paraffin Main ingredient in sticky wax

Sper macetti –From sperm whales wax Wax ester Used as a coating of dental floss

INLAY WAX INLAY WAX

COMPOSITION:

Paraffin 60 %Microcrystalline wax + ceresin 10 % Carnauba + candililla 25 %Bees wax 5 %

Deep blue, green, purple rods or sticks of 7.5 cm long & 0.64 cm in diameter

ADA S # 4 ISO 1561