Alternative technique to conventional casting for construction of metal substructure in metal ceramic restorations

PRESENTED BYTAREK AL-MORADIMASTER OF CROWN AND BRIDGE

SOHA MONEIRMASTER OF ENDODONTICS

Success in fabricating metal ceramic crowns and fixed partial

dentures depends to a large extent on obtaining high quality castings

that are properly designed and well fitting.

There are many methods of casting exist:

1- Conventional casting technique.

2- Alternative casting techniques.

1- Conventional casting technique:

The conventional lost wax technique has been used since ancient times to convert wax pattern to cast metal. The process consists of surrounding the wax pattern with a mold made of heat-resistant investment material, eliminating the wax by heating, and then introducing molten metal into the mold through a channel called the sprue.

The technique have 3 important topics to mention:

1- Construction of wax pattern. 2- Converting the wax into metal. a- Spruing. b- Investing. c- Wax elimination. d- Casting process. e- Evaluation & finishing. 3- Metal preparation to receive a ceramic

material. a- Investment removal. b- Surface grinding. c- Bonding of metal coping and ceramic

material through:

• Mechanical retention. 1- Sandblasting 2- Abrasion • Compression fit. • Chemical bond. 1- Oxidation 2- Precoating 3- Electrodeposition 4- Surface etching 5- Sputtering • Vander wall's force.

Casting Defects:

1-Roughness: The surface of a casting should be

smooth, although finishing and polishing are still required. Lines or grooves in the casting were usually present but overlooked in the wax pattern. They may necessitate a remake, particularly if they were positioned near the margin or the fitting surface. Generalized casting roughness may indicate a breakdown of the investment from excessive burnout temperature.

2-Nodules: Bubbles of gas trapped

between the wax pattern and the investment produce nodules on the casting surface. Even minute nodules can limit the seating of the casting to a considerable degree.

When they are large or situated on a margin they usually necessitate remaking of the restoration.When small, they can often be removed with a no.1/4 or 1/2 round bur .A binocular micro-scope is extremely helpful to detect and remove nodules.

Remove a slight excess of metal to ensure the nodule does not interfere with complete seating.

The key to avoiding nodules is a careful investing technique, a surfactant, vacuum spatulation, and careful coating of the wax pattern with investment. Castings made with phosphate-bonded investment are especially prone to such imperfections, and experience and care are required to produce castings that are routinely free of nodules.

• Rough casting

• Large nodules

• Multiple nodules

• Nodules on occlusal surface

3- Fins: Fins are caused by cracks in the

investment that have been filled with molten metal. These cracks can result from a weak mix of investment (high water-powder ratio), excessive casting force, steam generated from too-rapid heating, reheating an invested pattern, an improperly situated pattern (too close to the periphery of the casting ring), or even premature or rough handling of the ring after investing.

4- Incomplete casting: If an area of wax is too thin (less

than 0.3 mm), which occurs occasionally on the veneering surface of a metal-ceramic restoration, an incomplete casting may result.

Thickening of the wax in these areas is recommended. Incomplete casting of normal-thickness wax patterns may result from inadequate heating of the metal, incomplete wax elimination, excessive cooling ("freezing") of the mold, insufficient casting force, no enough metal.

5-Voids or Porosity: # Voids in the casting

(particularly in the margin area) may be caused by debris trapped in the mold (usually a particle of the investment undetected before wax elimination). A well-waxed smooth sprue helps prevent this.

# Porosity resulting from solidification shrinkage ("suck back") occurs if the metal in the sprue solidifies before the metal in the mold, as may happen when a sprue is too narrow, too long, or incorrectly located or when a large casting is made in the absence of a chill vent.

# Gases may dissolve in the molten alloy during melting and leave porosity defects.

# Back pressure porosity may be caused by air pressure in the mold as the molten metal enters. Its occurrence is reduced by using a more porous investment, locating the pattern near the end of the ring (6 to 8 mm), and casting with a vacuum technique.

• Incomplete casting

• Incomplete casting with shiny rounded edges

Suck-back porosity

Gas inclusion porosity

6- Marginal Discrepancies: Inaccuracies of fit at the

margin can be caused by distortion during removal of the wax pattern from the die. They may also result from increased setting expansion following uneven expansion of the mold.

7- Dimensional Inaccuracies: The casting can be either too

small or too large. Attention to detail is essential for an accurately expanded mold. A standardized procedure is needed in regards to liquid- powder ratio, spatulation, the ring liner, the amount of liquid added, and mold heating.

• Marginal discrepancy

Under or oversized restoration

Casting defects: Possible causes:

Incomplete casting Wax pattern too thinCool moldInsufficient molten metal

Incomplete casting with shiny rounded edges

Incomplete wax eliminationDebris trapped in the mold usually a particle of the investment

Suck-back porosity Metal in the sprue solidifies before the metal in the mold, as may happen when the sprue is too narrow , too long, or incorrectly located

Gas inclusion porosity Entrapment of gases in the molten alloys

Marginal discrepancy Wax pattern distortionUneven expansion

Under or Oversized restoration

Inadequate or excessive investment expansion

Back pressure porosity Inability of air to escape through investment pores due to :No ventingLong investment bridge

Rough casting Improper finishing of wax patternImproper W/P ratioExcessive burnout temperature

Large nodule Air trapped during investing procedure

Multiple nodulesInadequate vacuum during investingLack of surfactant

Nodules on occlusal surface

Excessive vibration

Fins Increased W/P ratioPattern too near edge of investmentPremature heating( mold still wet)Too rapid heatingDropped mold

2- Alternative casting techniques…….

Electroforming

CAD/CAM SYSTEM

Captek system

sintered powder technology

All Ceramic Restorations

Metal foil technology bonded platinum foil copingbonded platinum foil coping

Swaged gold alloy foil copingSwaged gold alloy foil coping

Procera allTitanProcera allTitan

Cicero systemCicero system

THE COMET SYSTEMTHE COMET SYSTEM

Titan systemTitan system

I) Electroforming (galvanioforming) technology

it’s the technique by which a thin it’s the technique by which a thin layer of pure gold is deposited on layer of pure gold is deposited on polyurethane dies that are coated polyurethane dies that are coated with a silver spacer using computer with a silver spacer using computer controlled platting equipment to controlled platting equipment to control thickness. control thickness.

The coping is plated with a noble The coping is plated with a noble paste primer before porcelain paste primer before porcelain application. This technique has been application. This technique has been developed to produce bioesthetic developed to produce bioesthetic metal-ceramic restoration.metal-ceramic restoration.

Different types of alloys can be used to Different types of alloys can be used to form coping by this technique as gold form coping by this technique as gold alloys, palladium alloys and non-alloys, palladium alloys and non-precious alloys. precious alloys.

AdvantagesAdvantages::DisadvantagesDisadvantages

Thin substructureThin substructure..Uncertain bond quality or Uncertain bond quality or porcelain to metalporcelain to metal

Economic and simplified Economic and simplified procedureprocedure..

Technique sensitiveTechnique sensitive

Coping strength is greater Coping strength is greater than other foilsthan other foils..

Coping strength lower than Coping strength lower than conventional castingconventional casting

Marginal adaptation of 15-20 Marginal adaptation of 15-20 umum

Unknown problems with creepUnknown problems with creep

No porosityNo porosity..

No opportunity for shrinkage No opportunity for shrinkage or expansion of the or expansion of the copingcoping

Helieform HF600 systemHelieform HF600 system::

This system uses an electroforming This system uses an electroforming technology to produce a thin pure gold technology to produce a thin pure gold coping. coping.

1.1. The gold is deposited on polyurethane The gold is deposited on polyurethane die that is coated with silver spacer using die that is coated with silver spacer using computer controlled led plating computer controlled led plating equipment to control thickness.equipment to control thickness.

1. Duplicate the working die with the polyurethane material.

2. Drill the polyurethane and glue the electrode into the die.

3. Apply an even coat of the silver spacer to the preparation and allow it to dry.

4. Insert the dies into the plating equipment. A magnetic stirrer ensures circulation of the cyanide-free gold sulfite solution.

5. Turn on the electric current, and gold will be deposited on the die at an approximate rate of 0.02 mm per hour.

6.6. After plating, the die is removed by After plating, the die is removed by heating and the silver spacer is removed heating and the silver spacer is removed with nitric acid or air abrasion.with nitric acid or air abrasion.

7.7. The surface of the coping is air abraded, The surface of the coping is air abraded, then coated with a noble metal paste then coated with a noble metal paste primer before porcelain application. This primer before porcelain application. This system has been adapted forsystem has been adapted for fixed fixed partial dentures.partial dentures.

II) metal foil technology:

A.A.bonded platinum foil bonded platinum foil coping:coping:

1- twin foil restorations.1- twin foil restorations.

2- bonded single foil restorations2- bonded single foil restorations

B.B.Swaged gold alloy foil copingSwaged gold alloy foil coping1-1- renaissance.renaissance.

2- sunrise2- sunrise..

A) A) bonded platinum bonded platinum foil copingfoil coping

twin foil restorationstwin foil restorations::

Porcelain can be bonded to platinum foil Porcelain can be bonded to platinum foil in such way that the die is covered with a in such way that the die is covered with a double layer of platinum. double layer of platinum. The inner layer is adapted on the die The inner layer is adapted on the die while the second layer is placed overall while the second layer is placed overall the die surfaces except the die surfaces except thethe shoulder shoulder This layer is bonded to the porcelain This layer is bonded to the porcelain after tin plating and it will prevent crack after tin plating and it will prevent crack formation. formation. The inner platinum foil is removed prior The inner platinum foil is removed prior to crown cementation.to crown cementation.

bonded single foil restorationsbonded single foil restorations : :

the single restoration utilizes only one the single restoration utilizes only one matrix, which is bonded to the core matrix, which is bonded to the core porcelain. porcelain.

Steps:Steps:1.1. the matrix is adapted till the cervical the matrix is adapted till the cervical

apron.apron. 2.2. Piece of rubber dam is punched and Piece of rubber dam is punched and

stretched over adapted matrix so that it stretched over adapted matrix so that it covers the shoulder and the matrix apron covers the shoulder and the matrix apron but not the axial walls. but not the axial walls.

3.3. The matrix is then air abraded with The matrix is then air abraded with aluminous oxides, where the abrasive aluminous oxides, where the abrasive particles will not affect the shoulder or particles will not affect the shoulder or the apron because of the rubber the apron because of the rubber covering.covering.

4.4. The abraded matrix is tin plated and The abraded matrix is tin plated and oxidized. oxidized.

5.5. Then opaque porcelain is applied, Then opaque porcelain is applied, followed by dentine and enamel.followed by dentine and enamel.

6.6. A scalpel is used to cut the single foil at A scalpel is used to cut the single foil at the point where plating stops.the point where plating stops.

Advantages:Advantages:

improved internal adaptation and improved internal adaptation and slightly greater strength when slightly greater strength when compared with twin foil tech.compared with twin foil tech.

B) Swaged gold alloy foil B) Swaged gold alloy foil coping:coping:

renaissancerenaissance::

Renaissance system is a laminated gold Renaissance system is a laminated gold alloy foil that is delivered to the user in alloy foil that is delivered to the user in fluted shape. The foil is placed over an fluted shape. The foil is placed over an epoxy die adapted and burnished. The epoxy die adapted and burnished. The final adaptation is achieved by swaging. final adaptation is achieved by swaging. The adapted, matrix is flame sintered to The adapted, matrix is flame sintered to form a coping. An interfacial alloy form a coping. An interfacial alloy powder is applied and fired and the powder is applied and fired and the coping is then veneered with porcelain.coping is then veneered with porcelain.

Advantage:Advantage:

Adequate strengthAdequate strength

Good marginal Good marginal adaptation adaptation

Ease of useEase of use

Disadvantage Disadvantage

Indicated for single Indicated for single anterior tooth onlyanterior tooth only

sunrisesunrise::

The sunrise system is another gold The sunrise system is another gold foil supported ceramic system that foil supported ceramic system that uses ceramco II porcelain. uses ceramco II porcelain.

Advantages:Advantages:

a yellow background a yellow background to porcelain to porcelain

ease of use ease of use

low costlow cost

good esthetic good esthetic

Disadvantage:Disadvantage:

Can use to single Can use to single restoration in which restoration in which occlusal stress is occlusal stress is minimal.minimal.

III) Captek system (capillary

technology):

FabricationFabrication1.1. Once the refractory dies Once the refractory dies

are prepared, the "P are prepared, the "P Material" is applied. Material" is applied. (Au-Pt-Pd layer)(Au-Pt-Pd layer)

2.2. The "P Material" is next The "P Material" is next pressed in the P-Press pressed in the P-Press and smoothed with an and smoothed with an an instrument.an instrument.

3.3. The "P Material" is then The "P Material" is then fired in the oven. This fired in the oven. This photo shows the photo shows the particles.particles.

4.4. After the "P Material" is After the "P Material" is fired, the "G Material" is fired, the "G Material" is applied and fired. applied and fired. (97%gold)(97%gold)

5.5. Through capillary action, Through capillary action, the "G Material the "G Material penetrates the "P penetrates the "P Material" so you end up Material" so you end up with gold on the inside with gold on the inside and outsideand outside

6.6. Finished metal.Finished metal.

AdvantagesAdvantages

Excellent esthetics Excellent esthetics

Excellent marginal adaptationExcellent marginal adaptation

Capek unlike other Dental Mental is Capek unlike other Dental Mental is NOT an alloy but a Composite. This NOT an alloy but a Composite. This

gives the metal a very high gives the metal a very high melting temperature and a melting temperature and a

capillary effect when applying capillary effect when applying porcelain. As shown in the cross porcelain. As shown in the cross

section below.section below.

IV) sintered powder

technology:

Degusint systemDegusint system::

It is an innovative method for It is an innovative method for manufacture of fixed dental manufacture of fixed dental prosthesis. prosthesis.

This method involves direct modeling This method involves direct modeling and sintering of precious metal alloy and sintering of precious metal alloy powder (gold) to form a restoration. powder (gold) to form a restoration.

The powder is first compactedThe powder is first compacted

then sintered during sintering then sintered during sintering process which is carried out below process which is carried out below the liquidus temperature of alloy.the liquidus temperature of alloy.

The powder particles form a The powder particles form a compact material, resulting in compact material, resulting in

sintering shrinkage which be kept to sintering shrinkage which be kept to minimum in order to achieve a minimum in order to achieve a

precise fit.precise fit.

The degusint system The degusint system achieves this by achieves this by employing specific employing specific grain size, shape, and grain size, shape, and distribution.distribution.

Degusint powder is Degusint powder is spherical; the grain size spherical; the grain size is adjusted so that the is adjusted so that the gaps between larger gaps between larger grains are filled with grains are filled with smaller ones, resulting smaller ones, resulting in high density.in high density.

This system is used for This system is used for fully fully anatomical inlay.anatomical inlay.

on lay.on lay.

crowns.crowns.

and metal substructure in and metal substructure in metal-ceramic restorationsmetal-ceramic restorations..

V) CAD/CAM process

The process can be use to prepare The process can be use to prepare metal inlays and crowns from alloys metal inlays and crowns from alloys that difficult to cast, such as pure that difficult to cast, such as pure titanium and titanium alloys.titanium and titanium alloys.

There is no need for either an There is no need for either an impression the prepared tooth or impression the prepared tooth or casting procedures. casting procedures.

There are many system used among which areThere are many system used among which are::

Minnesota system Minnesota system

computer aided-computer aided-prosthetic prosthetic system(CAP)system(CAP)

precident systemprecident system

micro-denta micro-denta systemsystem

titan system titan system

procera systemprocera system

Cicero systemCicero system

THE COMETTHE COMET SYSTEMSYSTEM

Procera system:Procera system:Procera allTitanProcera allTitan

This is a combination of copy milling This is a combination of copy milling and spark erosion tech. in which, the and spark erosion tech. in which, the external contour of the crown or external contour of the crown or coping can be shaped out of a solid coping can be shaped out of a solid piece of Ti or Ti-alloy by milling piece of Ti or Ti-alloy by milling machine. While the internal contour machine. While the internal contour is spark eroded with a carbon is spark eroded with a carbon electrode. electrode.

1.1. A stone die or replica A stone die or replica of the prepared of the prepared natural tooth was natural tooth was scanned using the scanned using the Procera Scanner Procera Scanner

2.2. the data transferred the data transferred to the computer were to the computer were used in the design used in the design process to develop process to develop specific specific characteristics for the characteristics for the coping. coping.

3.3. The coping was The coping was produced in titanium produced in titanium using electric using electric discharge machining discharge machining and copy milling and copy milling techniques to create techniques to create the restoration the restoration substructure substructure

4.4. a veneer material of a veneer material of low-fusing porcelain low-fusing porcelain was added to the was added to the coping to create the coping to create the anatomical and anatomical and occlusal requirements occlusal requirements in the restoration in the restoration

This process is used to prepared This process is used to prepared attachments, crowns and inlays from attachments, crowns and inlays from metals and alloys (Ti, Ti alloys). metals and alloys (Ti, Ti alloys). Multiple Procera AllTitan copings have Multiple Procera AllTitan copings have been used to fabricate the titanium been used to fabricate the titanium substructure for a fixed bridge substructure for a fixed bridge restoration. In this situation, the restoration. In this situation, the titanium units and a titanium pontic are titanium units and a titanium pontic are laser welded together to form the multi-laser welded together to form the multi-unit restoration.unit restoration.

DisadvantageDisadvantage::

The surface and color instability of The surface and color instability of low fusing porcelain.low fusing porcelain.

Titan systemTitan system: :

Its CAD/CAM system that produce metal Its CAD/CAM system that produce metal copings for porcelain fused to metal copings for porcelain fused to metal single and multiplesingle and multiple restorations. restorations.

This system uses stone dies fabricated This system uses stone dies fabricated from from regular impression techregular impression tech. however, . however, it uses a computerized mechanical mill to it uses a computerized mechanical mill to fabricate coping on bases of data recorded fabricate coping on bases of data recorded directly from the die surface and dose directly from the die surface and dose not not require Wax patternsrequire Wax patterns..

StepsSteps::1)1) digitizing from the digitizing from the

die surface. (From die surface. (From 3-8 min.)3-8 min.)

2)2) Mathematical Mathematical processing of data processing of data program (program program (program the computerized the computerized mill). (From 8-12 mill). (From 8-12 min.)min.)

3.3. Milling or processing Milling or processing of the copings from of the copings from discs or blocks of discs or blocks of titanium or other titanium or other alloys. (From 20-25 alloys. (From 20-25 min.)min.)

The milling process consists 3 The milling process consists 3 stepssteps

1.1. rough milling the inside of the rough milling the inside of the coping to remove the bulk of the coping to remove the bulk of the material.material.

2.2. Fine milling to increase the Fine milling to increase the accuracy.accuracy.

3.3. Rough external milling.Rough external milling.

The multiple unit restorations The multiple unit restorations constructed in the same way of the constructed in the same way of the single unit in addition to:single unit in addition to:

Determination of the position of the Determination of the position of the pontics.pontics.

determination of the shape and size determination of the shape and size of the connectors between unitsof the connectors between units

Cicero systemCicero system::

Its CAD/CAM system produce ceramic Its CAD/CAM system produce ceramic fused to metal restorations such as fused to metal restorations such as crowns, fixed partial dentures crowns, fixed partial dentures and inlaysand inlays with different layers as with different layers as metal dentin and incisal porcelain, metal dentin and incisal porcelain, for maximum strength and esthetics.for maximum strength and esthetics.

Cicero system makes use of a Cicero system makes use of a fast fast laser-stripe scanning methodlaser-stripe scanning method to to measure the three dimensional measure the three dimensional geometry of preparation and its geometry of preparation and its surrounding and opposing teeth.surrounding and opposing teeth.

StepsSteps : :1.1. vedio camera is used vedio camera is used

to scan the to scan the preparationpreparation

2.2. a computer calculates a computer calculates the pinots by the pinots by triangulation and triangulation and information is information is digitized from master digitized from master cast.cast.

3.3. Design of the Design of the restoration is restoration is manipulated by manipulated by dentist to choose the dentist to choose the best design.best design.

4.4. Cicero refractory Cicero refractory block block is fixed with is fixed with high precision in the high precision in the milling machine, and milling machine, and creating a refractory creating a refractory model.model.

5.5. Then sintering of a Then sintering of a thin layer of alloy thin layer of alloy powder on the powder on the refractory model is refractory model is done. The powder done. The powder consists of consists of aluminum-oxide–based ceramic

6.6. The Cicero porcelain The Cicero porcelain is then applied in the is then applied in the appropriate shade. A appropriate shade. A paste porcelain tablet paste porcelain tablet is pressed on metal is pressed on metal covered refractory die covered refractory die and fired under and fired under standardized standardized conditions vacuum in conditions vacuum in porcelain funace.porcelain funace.

7.7. The refractory block The refractory block is then replaced in is then replaced in the milling machine the milling machine to the interface of the to the interface of the porcelain and fired porcelain and fired

8.8. The external surface The external surface of the crown is then of the crown is then milled for milled for characterization of characterization of grooves, fossae and grooves, fossae and cusp lines.cusp lines.

9.9. Last step is individual Last step is individual staining and glazing of staining and glazing of the external surface.the external surface.

10.10. Finally, refractory die Finally, refractory die is removed by grinding is removed by grinding and air abrasion.and air abrasion.

THE COMET SYSTEMTHE COMET SYSTEMThe COMET system uses The COMET system uses

stone dies fabricated stone dies fabricated from impressions. from impressions.

Three steps are Three steps are involved: involved:

(1) Digitizing data from (1) Digitizing data from the die surface or a the die surface or a wax pattern surface.wax pattern surface.

(2) Mathematical (2) Mathematical processing of data to processing of data to program the milling program the milling machined.machined.

(3)Milling of copings, (3)Milling of copings, crowns, multiunit crowns, multiunit restorations, and restorations, and implant abutments.implant abutments.

1)1) An impression is obtained of the prepared An impression is obtained of the prepared abutments in the patient and the master abutments in the patient and the master cast poured in die stone. cast poured in die stone.

2)2) The planned restoration is then waxed The planned restoration is then waxed

3)3) wax pattern optoelectronically Scanned wax pattern optoelectronically Scanned and digitized.and digitized.

4)4) After removing the wax pattern from the After removing the wax pattern from the die, the surfaces of the abutments in the die, the surfaces of the abutments in the cast are digitized as well. cast are digitized as well.

5)5) The prepared abutment surface and contact and The prepared abutment surface and contact and occlusal surfaces of the adjacent and opposing occlusal surfaces of the adjacent and opposing teeth on the master model are digitized. teeth on the master model are digitized.

6)6) A CAD program is used to generate the new A CAD program is used to generate the new crown surface; whereas, the crown interior is crown surface; whereas, the crown interior is computed from the abutment surface data. computed from the abutment surface data.

7)7) For the production of custom copings, it is For the production of custom copings, it is sufficient to digitize the prepared abutment on sufficient to digitize the prepared abutment on the master cast. Exterior and interior surfaces of the master cast. Exterior and interior surfaces of the copings are computed by the software.the copings are computed by the software.

• This system can be used to construct:

• Single crowns, inlays, onlays, and FPD frameworks can be made of various metals or metal alloys, ceramics, or resin materials.

All Ceramic Restorations

1)1) Aluminous core Aluminous core ceramicceramic

2)2) Leucite reinforced Leucite reinforced porcelain porcelain

3)3) Glass ceramic: Glass ceramic: A.A. Dicor.Dicor.

B.B. CerapearlCerapearl

4)4) Injection-molded Injection-molded glass-ceramicsglass-ceramics

5)5) In-CeramIn-Ceram

6)6) Machined ceramic:Machined ceramic:A.A. CerecCerec

B.B. CelayCelay

C.C. Procera All Ceram Procera All Ceram systemsystem