Porcelains Used in Metal Ceramics / orthodontic courses by Indian dental academy

8/12/2019 Porcelains Used in Metal Ceramics / orthodontic courses by Indian dental academy

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PORCELAINS USED IN METALCERAMICS.

INDIAN DENTAL ACADEMY

Leader in continuing dental education

www.indiandentalacademy.com




INTRODUCTION

Metal ceramic restorations

combine the strength and

accuracy of cast metal with the

esthetics of porcelain.

Indian dental academywww.indiandentalacademy.com



Metal ceramic restoration:

• "a fixed restoration that

employs a metal substructure

on which a ceramic veneer isfused" (Glossary of

Prosthodontic Terms, 1987).

• Indian dental academy




A 13- unit metal-ceramic

restoration.




• HISTORY/ DEVELOPMENT OF

CERAMICS.

• PROPERTIES OF FUSEDPORCELAIN.

• TERMINOLOGY• CHEMISTRY & COMPOSITION

• CLASSIFICATION OF DENTAL

CERAMICS.




• METAL CERAMIC SUBSTRUCTURE

• BONDING BETWEEN THE METAL

DESIGN & PORCELAIN• PORCELAIN APPLICATION

METHOD

• FIRING PROCEDURES• FINISHING & ADJUSTMENTS

Metal ceramic technology.




• The word Ceramics is derived

from Greek word ―keramos‖

which means ‗pottery‘ or ‗burntstuff‘.

Porcelain in English means

―china‖.




Ceramics

Compounds of one or more metalswith a non metallic element,

usually oxygen. They are formedof chemical and biochemicalstable substances that are strong,

hard , brittle, and inert nonconductors of thermal andelectrical energy(GPT-7).




Porcelain is defined as

A ceramic material formed ofinfusible elements joined by lowerfusing materials. Most dentalporcelain are glasses and areused in the fabrication of teeth fordentures, pontics and facings,

metal ceramic restorations,crowns, inlays, onlays, and otherrestorations.




er es gna ons o me aceramics

• Porcelain-fused to metal.

• Ceramo-metal crown.

• Porcelain veneer crown.

• Porcelain bonded to metal

crown.




Structure of ceramics

• Their atomic structure and resultant

properties depend, not only on

composition, but also on thermal history.

•Dental porcelain are glassy materials

Glasses may be regarded as a super cooled

liquids or as non crystalline solids




History

• CHINESE ARE CREDITED WITHTHE DEVELOPMENT OF

PORCELAIN AS EARLY AS 1000

AD.• D‘ENTRECOLLES, INGRATIED

HIMSELF WITH CHINESE

POTTERS AROUND 1717 INORDER TO LEARN THE COVETED

PORCELAIN MANUFACTURING

PROCESS www.indiandentalacademy.com



• IN 1760 FAUCHARD AND OTHERS

HAD REPORTED USING ‗BAKEDENAMEL.

• IN 1774 ALEXIS DUCHATEAU &

NICOLAS DUBOIUS

CONSTRUCTED COMPLETE

DENTURES FROM A MATERIAL

THEY REFERRED TO AS ―MINERAL

PASTE‖.




• IN 1808 GIUSSEPPANGELO FONZI

DEVISED A METHOD TO MASS

PRODUCE INDIVIDUALPORCELAIN DENTURE TEETH




• 1850 Samuel Stockton was the first to

mass produce these teeth first in America

• Claudius Ash created a artificial tooth

that could be placed over a post on

either a complete denture of FPD. Itwas known as ―tube‖ tooth.




• 1889 Dr Charles H. Land gave the

idea of fusing porcelain to a thin

platinum foil. – he developed lowfusing porcelain in 1898. 1903 he

introduced the porcelain jacket crown

to dentistry




• 1907 Stockton developed dental

porcelain.

• 1962 –M. Weinstein, S.Katz, and

A.B.Weinstein patented a method tofabricate the first metal ceramic

crown.




• Two of the most important breakthroughs

responsible for the long-standing superbaesthetic performance and clinical

survivability of metal-ceramic restorations

are the patents of Weinstein and

Weinstein (1962) and Weinstein et al

(1962).

• One of these patents described the

formulations of feldspathic porcelain that

allowed systematic control of the sintering

temperature and thermal expansion

coefficient. www.indiandentalacademy.com



• The other patent described the

components that could be

used to produce alloys thatbonded chemically to and

were thermally compatible withfeldspathic porcelains




What are ceramics?

–Dental ceramics may consistprimarily of glasses ,porcelains,

glass-ceramics.

–The properties of ceramics arecustomized for dental application

by precise control of the type &

amount of the components usedin their production.




• Ceramics are more resistant to

corrosion. Ceramics generally donot react with most liquids, gases,

alkalies & acids. And they remain

stable over long time.• Dental ceramics exhibit far to

excellent flexure strength & fracture

toughness.




• Although ceramics are strong,

temperature-resistant & resilient

these materials are brittle and mayfracture when quickly heated and

cooled.

• Dental ceramics are non-metallic

inorganic structures,primarily

containing components of oxygen

with one or more metallic or semi

metallic elements.




• Most ceramics arecharacterized by their refractory

nature, high hardness,(relatively low tensile strengthand essentially zero percent

elongation), and chemicalinertness.

Properties of ceramics.




• For dental applications a

hardness of a ceramic less thanthat of enamel and an easily

polishable surface are desirableto minimize the wear damage that

can be produced on enamel by

the ceramic surface.




1) Strength.

• Porcelain is a material having good

strength. However, it is brittle and

tends to fracture.• The strength of porcelain is usually

measured in terms of its flexure

strength or modulus of rupture.




a) Flexure strength:

• It is a combination of compressive,

tensile, as well as shear strength.

• Glazed porcelain is stronger thanground porcelain.

• Ground-75.8 Mpa (11,000 psi)

• Glazed-141.1 Mpa (20,465 psi)




b) Compressive strength:

• Porcelains have good compressive

strength.

• 331 Mpa (48,000psi)




c) Tensile strength:

• Is low

• 34 MPa (5000psi).




d) Shear strength:

• It is low and is due to the ductility

caused by the complex structure of

dental porcelain.• 110 Mpa (16000psi).




Factors affecting strength.

• 1) Composition.

• 2) Surface integrity: Surface imperfections

like microscopic cracks and porosities

reduce the strength.

• 3) Firing procedure: Inadequate firing

weakens the structure as vitrification is not

complete. Overfiring also decrease

strength as more of the core gets

dissolved in the fluxes, thereby weakening

the core network.www.indiandentalacademy.com



2) Modulus of elasticity:

• Porcelain as high modulus of

elasticity.

• 69 GPa .




3) Surface hardness:

• Porcelain is much harder than natural

teeth.

• 460 KHN




4) Wear resistance:

• Porcelain is more resistant to wear

than natural teeth. Thus, it should not

be placed opposite to natural teeth.




5) Specific gravity:

• Is 2.242.

• The specific gravity of fired porcelain

is usually less, because of thepresence of air voids. It varies from

2.2 to 2.3.




6) Dimensional stability:

• Porcelain is dimensionally stable after

firing.




7) Chemical stability:

• It is insoluble and impermeable to oral

fluids. Also it is resistant to most

solvents. However, contact withhydrofluoric acid causes etching of

the porcelain surface.




8) Esthetic properties:

• Are excellent. It is able to match

adjacent tooth structure in

translucence, color and intensity.




9) Biocompatibility.

• It is compatible with the oral tissue.


10) Th l tibilit



• Refers to the ability of a metal

and its veneering porcelain tocontract at similar rates.

• The coefficient of thermalexpansion by definition is thechange in length per unit of

original length of a material whenits temperature is raised by 1o K

• .

10) Thermal compatibility




Thermal compatibility (contd.)

• When the co efficient of thermalexpansion of metal and porcelainare compatible the tensile stressthat develop during cooling areinsufficient to cause immediate

cracking of porcelain or delayedcracking after cooling at roomtemperature.




• Porcelains have coefficient of thermal

expansion between 13.0 and 14.0 X

10-6 and metal between 13.5 and14.5 X 10-6.

• The difference of 0.5 X10-6 in thermal

expansion between metal andporcelain causes the metal to contract

slightly more than does the ceramic

during cooling after firing the

porcelain.




• This puts the ceramic under

slight residual compression

which makes it less sensitiveto applied tensile forces.




Methods of strengthening ceramics

• Strengthening occurs through two

mechanism,

• 1) development of residualcompressive stresses.

• 2) interruption of crack propagation.




• Development of residual compressive

stresses.

• 1) Ion exchange: (chemicaltempering)

• exchange of potassium ions (which is

35% larger) for sodium ions. thus

there is squeezing of the potassium

ion into smaller spaces. This creates

a residual compressive stresses on

the surface of the glass.




• Thermal tempering.

• By rapidly cooling the surface of the

object while it is hot and in the moltenstate. This rapid cooling produces a

layer of rigid glass surrounding a soft

core. As the molten core solidifies ,it

tends to shrink, creates a residual

tensile stress in the core thus leaving

the outer layer in residual

compressive stress.


S O CO C



• THERMAL EXPANSION COEFFICIENT

MISMATCH:

• Ceramic in combination with metal areheated together .The metal which is

veneered with ceramic has a higher

coefficient of thermal expansion than the

ceramic. Hence on cooling, the metal

contracts more than the ceramics thus

leaving the outer layer, of ceramic in

residual compressive stress.


Interr ption of crack propagation



Interruption of crack propagation.

• Two different types of dispersions used to

interrupt crack propagation are:

• 1) By absorption of energy by the

dispersed tough particle from the crack

and thus depleting its driving force for

propagation.

• 2) By change of crystal structure under

stress to absorb energy from the crack.


1) Di i f t lli



1) Dispersion of a crystalline

phase.

• A tough crystalline material like alumina is

added in particulate form. The glass is

toughened and strengthened because the

crack cannot penetrate the aluminaparticles as easily as it can propagate in

the glass. Thus the aluminous porcelains

were developed for Porcelain JacketCrown. (PJC)




Transformation toughening.

• A crystalline material is incorporated that

is capable of undergoing a change in

crystal structure when placed under

stress. The crystalline material used istermed as partially stabilized zirconia

(PSZ).The refractive index of PSZ is

higher than glass matrix. Thus the PSZscatters the light producing an opacifying

effect.




Terminology.

Porcelain-fused-to-metal (PFM): a

popular alternative designation

for the metal ceramic restoration.




• Porcelain bonding: a term used toexplain the mechanisms by which

dental porcelain fuses or adheres to ametal substructure

• Coping: the word coping can be used toidentify the metal substructure of single-unit crowns designed for bonding todental porcelain. Copings are made ona single tooth preparation, which may

be a single unit or attached to ponticsfor a fixed partial denture.




• Framework: this term is often applied

to fixed partial dentures and identifiesa one-piece substructure composed

on either several copings attached to

a pontic or multiple single units thatare joined together as a single

structure.




• Degassing: the process of heat-treatinga cast metal substructure in a porcelain

furnace as one of the preparatory stepsto applying an opaque porcelain.Subjecting the finished metal toelevated temperatures (980° to

1,050°C) in a reduced atmosphere(vacuum) or in air reportedly burns offorganic surface impurities andeliminates entrapped gaseous

contaminants. A newer and perhapsmore appropriate term—oxidizing—hasemerged in the literature to describe this

procedure. www.indiandentalacademy.com



• Oxidation (or oxidizing): the

process by which a metalsubstructure is heated in a

porcelain furnace to produce an

oxide layer for porcelain bondingas well as to cleanse the

porcelain-bearing surfaces of

contaminants


ADVANTAGES OF DENTAL



ADVANTAGES OF DENTAL

PORCELAIN

• Dental ceramics are attractive

because of their biocompatibility,

long-term color stability, wear

resistance, and their ability to be

formed into precise shapes.




Disadvantages.

• They require costly processing

equipment and specialized

training.• Susceptibility to brittle fracture

at relatively low stresses


The chemical components of dental



The chemical components of dental

porcelain.

• Feldspar (K2O – Al 2O3-6SiO2 & Na2o –

Al2o3-6SiO2)

• Quartz (SiO2)

• Alumina (Al2O3)

• Kaolin (Al2O3 -2SiO2 2H2O)




Feldspar

• Found as a mix of two substances .• It does not occur in pure form in

nature

• Mineral is crystalline and opaque

• Color is indefinite and between gray

and pink.


Type of Chemical Other Properties uses



Type of

feldspar

Chemical

formula

Other

names

Properties uses

Potassiu

m

aluminiu

m

silicate.

(K2O.Al

2O

3.6Si

O2 )

orthocla

se or

potashfeldspar

1.Reduces the

fluidity of the molten

materials

2.helps to maintain

the form of the

porcelain buildup

3.adds translucent

qualities to fired

restorations.

Found in

majority

of the

porcelain

systems

Sodium

aluminu

m

silicate

(Na2O.

Al2O3.

6SiO2)

albite or

sodiumfeldspar

.

1.Lowers fusion

temperature of the

porcelain.

Less

preferred

Lime

feldspar

CaO.2

Al2O3.2www.indiandentalacademy.com



• On heating it becomes glassy and

fuses at 1290 C, on overheating itmay loose its shape .

• Impurities : Mica

Iron –it is important to

remove it as its oxides act as strong

coloring agents.




Removal of impurities

Iron-

• manually only light colored pieces of

feldspar are selected• Feldspar is grounded into fine powder

and vibrated down inclined planes

surrounded by induction magnets




• Primarily responsible for forming

glass matrix

Functions




• Glass modifiers such as the oxides of

potassium, sodium, and calcium acts

as fluxes to increase a porcelains

coefficient of thermal expansion.

• The fluxes increase the porcelainscoefficient of thermal expansion by

breaking up oxygen crosslinking.




• Primarily responsible for

forming glass matrix

• Has a fusion temperature

Silica (Quartz or Flint) SiO2




SiO2




• Silica contributes stability to the

mass of porcelain during heating

by providing a framework for theother ingredients.

• Also acts to strengthen the

porcelain.

Functions




KAOLIN (Al2 o3-2sio22H2o)

• It is deposited along the banks and at the

bottom of streams in the form of clay.•

Only purest form of clay are used fordental porcelain.


f



Preparation of clay

• Repeated washing until all foreign

materials are separated.

• Allowed to settle.• Dried and screened.

• Nearly white powder is obtained.


Properties of clay



Properties of clay

I. Its gives OPAQUENESS to porcelain

II. MOULDABLE :On mixing with water itbecomes sticky and aids in forming a

workable mass of the porcelain duringmolding.

III. Clay-water suspension maintains itsshape during firing in a furnace.

IV. On subjecting to high heat it adheres tothe framework of Quartz particles andshrinks considerably.




• Little or no kaolin is found is

modern day low fusing

porcelain.

• Kaolin is not used in enamelpowder as it will decrease its

translucency.


Alumina (Al o )



Alumina.(Al2o3)

• The hardest and perhaps the

strongest oxide.

• Its CTE is similar to the low fusingporcelains.

• It also strengthens the porcelain.


Manufacturing of ceramics



Manufacturing of ceramics

powder




Fritting.

• The process of blending, melting andquenching the glass components istermed ―fritting‖.

• All the raw mineral powders are mixedtogether in a refractory crucible andheated till a molten mass is formed.

• It is then quenched in water.

• It immediately breaks into fragments andthis is termed the ―frit‖.




• Frits are ground to the specific particle

size established by individual

manufacturers for their particular brand of

porcelain.




• TOOTH PREPARATION FOR

THE METAL CERAMIC

RESTORATION




• Depth

orientation

grooves flatend tapered

diamond.




• Make at least

two verticalcuts in the

incisal portionof the facial

surface.




• Sink the side of

the diamond intothe mesiodistal

center of the

facial

surface,maintain

the instrument

alignment parallel

to the gingivalsurface of the

facial segment.




• Make two incisal

orientation grooves

that are 2mm

deep.The diamondshould be parallel to

the incisal edge

faciolingally.




• Incisal

reduction is

done with the

flat end tapered

diamond.




• Facialreduction;

incisal half,flat

end tapereddiamond.




• If there soundtooth structure

inter proximally,

wingpreparation is

done.




• Begin the lingual

reduction with thesmall round

diamond with

diameter of

1.4mm. Sink this

instrument into

the lingual tooth

structure up to0.7mm.




• Lingual axial reduction

torpedo diamond and carbidefinishing bur.




• Lingual

reduction is

done with thesmall wheel

diamond.




• Smooth the entire

facial surface with

no.171 bur .Round

over the any sharp

angles on the incisal

angle or along the

edges of the incisalnotches with no.171

bur.


Components of the metal



Components of the metal

ceramic restoration

• Two major components:

• a metal substructure and a porcelain

veneer.• The surface oxide layer that lies

between the metal and the porcelain

veneer could be considered aseparate component, but it is anintegral part of the casting alloy

substructurewww.indiandentalacademy.com




The basic components of a traditional



The basic components of a traditional

porcelain kit include

1.opaque porcelain.

2.dentin porcelains

3.enamel porcelainsModifiers, stains & glazes.

Newest products has high fusing

shoulder porcelains.


The metal substructure



• Conventional low-fusing dental

porcelain lacks the strengthrequired of an all-porcelainrestoration, so a metal substructureis added to support the porcelainveneer.

• The thickness of the metal copingcan vary, depending on the type ofcasting alloy used and the amountof tooth structure reduced by thedentist.


The oxide layer



y

• Most metal ceramic alloys are

oxidized after the porcelain-

bearing area of the restoration hasbeen properly finished and

cleaned.


• The metal oxides that form on the



The metal oxides that form on thealloy's surface during this heat-

treatment procedure play a key rolein bonding the dental porcelain tothe underlying metal substructure.

• Because noble elements do notoxidize, an alloy's base metalconstituents are principally

responsible for forming this oxidelayer.


• Differences in alloy composition



Differences in alloy composition

require that oxidation techniques be

alloy specific

• Ideally this oxidation should be no

more than a discrete, monomolecular

film on the alloy's surface for all metal

ceramic alloys, irrespective ofcompositional differences.


Opaque porcelain layer



Opaque porcelain layer

• These porcelains are made opaque by theaddition of insoluble oxides, such as

• tin oxide (SnO2),

• titanium oxide (TiO2),

• zirconium oxide (ZrO2),

• cerium oxide (CeO2),


Opaque porcelain layer contd



Opaque porcelain layer contd.

• oxide, and

• rubidium oxide,

• barium zinc oxide.• Such oxides have high refractive

indices, so they scatter light.


Composition on chemical



analysis


• Between 8% and 15% of an opaque



• Between 8% and 15% of an opaque

powder is composed of metallic

oxides, and some particles may beless than 5 um in size.

• Even small differences in particle sizedistribution are thought to influence

the ability of opaques to mask the

color of a metal substructure.


Th l i th j



• The opaque porcelains three major

functions:

• (1) to establish the porcelain-metal

bond,

• (2) to mask the dark color of themetal substructure, and

• (3) to initiate the development of

the selected shade of porcelain.




• A uniform thickness of 0.2 to 0.3

mm generally is regarded as ideal.

• That masking power is influencedby the amount and the color of the

oxidized (degassed) metal casting

(Naylor, 1986)


• A casting alloy of a different



A casting alloy of a different

composition might generate a thick,

dark oxide layer (Naylor, 1986) andrequire a thicker opaque covering.

• The thickness of the opaque layer

needed to veneer the metal and

mask the surface oxides differs

among brands of porcelain and

even varies for different shades

within the same porcelain system





Body porcelains



y p

• Body porcelain collectively describes

four principal types of porcelain

powders used to recreate the "body" of

a restoration: dentin (body or gingival),

enamel (or incisal), translucent, andmodifier.

• These body porcelains are mixed with

either distilled water or a special liquid(provided with the porcelain kit) that

helps to prevent the buildup from drying

out rapidly www.indiandentalacademy.com

• They are applied directly over the fired



• They are applied directly over the fired

opaque layer .

• The dentin, enamel, translucent, and

modifier powders all have the same

chemical and physical properties, they

may be intermixed freely if customshading is desired.

• They differ in appearance in the fired

state because of variations in theamount and type of metallic oxide

pigments each contains.


The dentin porcelain veneer



• The major color contribution is derivedfrom the pigmented metal oxides in thedentin body porcelain

• It is this initial layer of dental porcelainthat imparts the dentin shade

associated with, but not confined to, thegingival two thirds of a tooth.

• The dentinal layer is overbuilt slightly,cut back, and overlaid with enamelporcelain in those sections of therestoration where greater translucencyis desired.


F t h d



• For more accurate shade

duplication, estimates of thecombined thickness of fired dentin

and enamel porcelains range from

a minimum of 0.5 to 1.0 mm to amaximum thickness of 1.5 to 2.0

mm


• For uniformity of shade and maximum



y

strength, it is desirable to have an even

thickness of porcelain covering themetal substructure.

• The minimum total thickness of

porcelain may be between 1.2 to 1.3mm at the middle one third of the

restoration and 1.5 to 1.6 mm at the

incisal edge (Yamamoto, 1985).


ENAMEL PORCELAIN VENEER



ENAMEL PORCELAIN VENEER

• Enamel porcelains are moretranslucent than dentin porcelains.

• The enamel porcelains are usually in

the violet to grayish range & impart acombination of true translucency &

the illusion of the translucency by

virtue of their grayish or some timesbluish appearance.

• www.indiandentalacademy.com

• When fired, enamel porcelains are more



When fired, enamel porcelains are more

translucent than dentin porcelains

(McLean, 1979).• They also have a more restricted range

of shades. A typical porcelain system

may provide only four or five bottles ofenamel powders to cover the entire

range of shades in the kit.


Translucent porcelains



Translucent porcelains

• Translucent porcelains are nottransparent, they do not allow the

transmission of all light.

• They are applied as a veneer over nearlythe entire surface of a typical porcelain

buildup.

• This veneer imparts depth and a naturalenamel-like translucency without

substantially altering the body shade that

is overlaid www.indiandentalacademy.com

BODY MODIFIERS



• These porcelains are more color concentrated &were designed to aid in the achieving internal

color modifications.

• They are used to distinguish the dentin, enamel

& translucent porcelains, because they have the

same basic physical & chemical properties.

• All these powders are basically same materials,

they do differ in the appearance because of themodifiers.

BODY MODIFIERS





STAINS



• Stain powders contain less silica oralumina & more sodium & potassium

oxides.

• They contain high concentration of

metallic oxides.

• They are created by mixing themetallic oxides with lower fusion point

glasses

STAINS


GLAZES



GLAZES

• Glazes are generally colorless, low fusingporcelains.

• They possess considerable fluidity at high

temperatures.• They fill small surface porosities &

irregularities. when fired helps to recreate

the external glazy appearance of thenatural tooth





GLAZE (Contd.)



GLAZE (Contd.)

• A glazed ceramic surface isgenerally considered beneficial by

increasing the fracture resistanceand reducing the potential

abrasiveness of ceramic surfaces


Color coding



Color coding

• By convention dentin powders are pinkand enamel powders are blue.

• These organic colors burn off during firing

procedure and do not affect the shade ofthe fired restoration in any way.

• Some manufacturers color code the

distilled water instead of the powder.e.g.pencraft porcelain


CLASSIFICATION OF DENTAL

CERAMICS



CERAMICS

• Different types of dental ceramics areavailable These include core ceramic,

liner ceramic, margin ceramic,

opaque dentin (also, body or gingival)ceramic, dentin ceramic, enamel

(incisal) ceramic, stain ceramic, glaze

ceramic, and addition ceramic


• These products can be



classified in several possible

ways according to their: (1) useor indications (anterior,posterior, crowns, veneers, post

and cores, FPDs, stain ceramic,and glaze ceramic);


• (2) composition (pure alumina



• (2) composition (pure alumina,

pure zirconia, silica glass, leucite-based glass-ceramic, and lithia-

based glass-ceramic

• (3) processing method (sintering,partial sintering and glass infiltration

,CAD-CAM, and copy-milling);




• Microstructure (glass, crystalline,and crystal-containing glass);

• Translucency (opaque,translucent, and transparent);

Fracture resistance; or

Abrasiveness


Based on the method of fabrication



1. Condensation porcelains usingcondensation and sintering

2. Castable ceramics –Dicor-Dentsply

3. Pressable ceramics

4. Machinable ceramics

5. Infiltrated ceramics

6. Injection molded ceramics –Cerestore


Classification (Mclean)



1) Regular feldspathic porcelain

2) Aluminous porcelain

3) Metal bonding porcelain.

( )


Based on their fusion temperature (Phillips,1982)type Fusing

temperature

uses



temperature

range

High fusingporcelains-

1288 to 1371C

1200-1400

used formanufacturing

denture teeth .

Both aresimilar in

composition

and

microstructure.

Medium fusing

Porcelains-

1093 to 1260

C

1050-1200

for all ceramic

restorations

and

prefabricatedpontics.

Low fusing

porcelains-

871 to 1066 C

800-1050

for metal

ceramic and all

ceramic.www.indiandentalacademy.com

METAL SUB STRUCTURE

DESIGN



DESIGN.

• Majority of the porcelain-to-metal bondfailures occur as a direct result of improper

substructure design

• Errors in the preparation of the metalceramic substructure frequently go

unnoticed until the brittle porcelain veneer

fails in service.


METAL SUB STRUCTURE

DESIGN



• TYPES

• FUNCTIONS.

• DESIGN.

DESIGN.


Types of metal ceramic system.A C l i ll



• A. Cast metal ceramic alloys:

• 1.Noble-metal alloy systems:• High gold - a) Gold platinum palladium.

• Low gold - b) Gold palladium silver.

• Gold free - c) Palladium silver.• 2.Base metal alloys systems:

• Nickel chromium alloy.

• Cobalt chromium alloys ( rarely used inceramic bonding).


• B. Foil copings:



g

•

• a) Bonded platinum foil coping.

• b) Swaged gold alloy foil coping.


a) Bonded platinum foil coping:



) p p g

• Another method of bonding porcelain tometal is the use of tin oxide coatings onplatinum foil.

• The method consists of bondingaluminous porcelain to platinum foilcopings.

• Attachment of the porcelain is secured by

electroplating the foil with a thin layer of tinand then oxidizing it in a furnace.




• The objective of this type ofrestoration is to improve esthetics.

• The thicker cast metal coping that is

normally used is replaced by a thinner

platinum foil, thus allowing more

space for the porcelain.


b) Swaged Gold Alloy Foil Coping:



• A laminated gold alloy supplied in flutedshape is also used as an alternative to the

cast metal coping.

• The foil is swaged onto the die and flamesintered to form a coping.

• An ―interfacial alloy‖ powder is applied

and fired and the coping is then veneeredwith porcelain.


Primary functions:-



• The casting provides fit of the

restoration to the prepared tooth.

• The metal forms oxides that bondchemically to the dental porcelain.


• The coping serves as a rigid



• The coping serves as a rigid

foundation to which the brittleporcelain can be attached for

increased strength & support.

• The sub structure restores the

tooth's proper emergence profile.


Secondary functions.



• Metal occlusal & lingual articulatingsurfaces generally less destructive to

the enamel of the opposing natural

tooth.

• Fabrication of the restoration with

minimal occlusal clearance has more

potential for the success with metal

substructure than all ceramic alloys.




Metal sub structure design



• Majority of the porcelain-to-metalbond failures occur as a direct result

of improper substructure design

• Errors in the preparation of the metal

ceramic substructure frequently go

unnoticed until the brittle porcelain

veneer fails in service.


Sub structure design (contd)



• Hence necessary to understandthe essentials of proper

substructure design, since it will

help to ensure the longevity of the

final prosthesis.


Principles of substructure

design



design.

• Are the occlusal contacts to bein metal or porcelain?


• Occlusion in metal requires less tooth



q

reduction (1 to 1.5 mm).

• Approximately 2 mm of occlusal

reduction is necessary for posterior

teeth and 1 to 1.5 mm for anteriorteeth requiring porcelain on occluding

surfaces.


• Metal surfaces can be more easily



y

adjusted and repolished at chair side

without adversely affecting the

restoration.

• On the other hand, removing theglaze of a metal ceramic restoration

during intraoral adjustments weakens

the porcelain greatly




• 2. Are the centric occlusalcontacts 1.5 to 2mm from the

porcelain-metal junction?


• occlusal contacts when placed

directly on or close to the porcelain-



directly on or close to the porcelain-

metal junction, there is an increasedlikelihood the porcelain will chip or

fracture at that point of contact .

• Porcelain is strongest undercompression and weakest under

tension, so situations that induce

tensile stresses in the ceramic duringfunction are more apt to promote

bond failureswww.indiandentalacademy.com

• A substructure should be designed so



g

the functional incisal or occlusal

contacts are located at least 1 .5 mm

and perhaps as much as 2 mm from

the metalporcelain junction.




• Do not



design the

sub structure

so contact

occurs at theporcelain

metal

junction.


• When the anteriorteeth occlude in thei i l h lf f th



gingival half of the

maxillary teeth orwhen the lingualtooth reduction isless than 1mm it is

best to design thesub structure withocclusion in themetal.




• 3.Are the interproximal contactsto be restored in metal or

porcelain?


• The inter proximal contact areas of



anterior teeth, and at least the mesial

contacts of posterior teeth, are

frequently restored in porcelain

• with porcelain inter proximal contactareas would be more esthetic,

particularly with anterior teeth.


• It is important to provide proper metal

t t l i i l id



support to a porcelain marginal ridge

in the substructure design to preventpossible fracture

• However, the distal inter proximal

contacts of posterior teeth may be

restored in either metal or porcelain

because these areas are not as

critical esthetically.




• The ultimate goal of any substructure

is to support an even thickness (1mm



pp (

minimum, 2 mm maximum) of theporcelain veneer.

• If this maximum thickness is

exceeded, the ceramic layer may nolonger be properly supported,

resulting in a catastrophic failure at

the cusp tip or incisal edge




• 5. Is the substructure thickenough to provide a rigid

foundation for the porcelain

veneer?


• Areas to be veneered with

l i t b t l t 0 3



porcelain must be at least 0.3 mm

thick.

• with base metal alloys, the

coping can be reduced to 0.2 mmor less and still be strong enough

to support the porcelain


How does dental porcelain bond to

metal?



metal?

(1) van der Waals forces (Lacy, 1977),• (2) mechanical retention,

• (3) compression bonding, and

• (4) direct chemical bonding (Lacy,

1977; McLean, 1980;


van der Waals forces



• The attraction between chargedatoms that are in intimate contact yetdo not actually exchange electrons isderived from van der Waals forces.

• These secondary forces aregenerated more by a physicalattraction between charged particles

• Van der Waalsforces are generallyweak.





• The better the wetting of the



The better the wetting of the

metal surface, the greater the vander Waals forces.

• porcelain's adhesion to metal can

be diminished or enhanced by

alterations in the surface

character (texture) of theporcelain-bearing surface on the

substructurewww.indiandentalacademy.com



• van der Waals forces are onlyminor contributors to the overall

attachment process.


Th l i b i f t l

Mechanical retention



• The porcelain-bearing area of a metal

casting contains many microscopicirregularities into which opaque

porcelain may flow when fired.

• Air abrading the metal with aluminum

oxide is believed to enhance

mechanical retention further by

eliminating surface irregularities

(stress concentrations)www.indiandentalacademy.com

• Mechanical retention's



Mechanical retention s

contribution to bonding may berelatively limited.

• Dental porcelain does not require

a roughened area to bond to

metal but some surface

roughness is effective inincreasing bonding forces





Compression bonding



• Dental porcelain is strongest undercompression and weakest under

tension; hence, if the coefficient of

thermal expansion of the metalsubstrate is greater than that of the

porcelain placed over it, the porcelain

should be placed under compressionon cooling


• the metal contracts faster than the



porcelain but is resisted by theporcelain's lower coefficient of

thermal expansion.

• This difference in contraction

rates creates tensile forces on the

metal and correspondingcompressive forces on the

porcelain.www.indiandentalacademy.com

Chemical bonding



• The single most significantmechanism of porcelain-metal

attachment is a chemical bondbetween dental porcelain and the

oxides on the surface of the metal

substructure


• The two hypothesis that explains

chemical bonding are



chemical bonding are

• 1, The sandwich theory

the oxide layer is permanently

bonded to the metal substructure on

one side while the dental porcelain

remains on the other


• The oxide layer itself is



The oxide layer itself is

sandwiched in between the metalsubstructure and the opaque

porcelain. This "sandwich" theory

is undesirable in that a thick oxidelayer might exist that would

weaken the attachment of metalto porcelain




• Chemical "bonding" is generallyaccepted as the primary

mechanism in the porcelain-metal

attachment process




The oxidation (degassing) process

Aft th t t l i



• After the cast metal ceramiccastings have been properlyfinished with uncontaminatedcarbide burs or ceramic abrasivesthe castings are heat-treated in aporcelain furnace (in air or a

vacuum) to a designatedtemperature for a specified periodof time (Naylor, 1986).


• The heat-treatment process



allows specific oxides to form onthe metal surface. These oxides

are responsible for the chemical

porcelain- metal "bond."


• A high-gold-content alloy contains

oxidizable trace elements such as tin



oxidizable trace elements such as tin,

indium, and iron to produce anadherent oxide layer. Because

elements like gold and the other noble

metals do not oxidize, it is often

necessary to hold these castings at

temperature for several minutes to

permit the non noble trace elements

to form the oxide layerwww.indiandentalacademy.com

• The base metal alloys readilyoxidize, but trace elements are



still added in an effort to form aparticular type of oxide for astable bond .

• The oxidation procedure may becarried out in a vacuum tominimize the amount of oxidation,

and the hold time is often reducedor omitted.





• A properly oxidized casting often

has a distinctive appearance in



terms of color and character(texture, thickness, etc).

• That appearance of a properly

oxidized metal substructure differs

among alloy systems and may

also differ among alloys within thesame system.




• Some manufacturers do notrecommend an oxidation/

degassing step; instead, they

advocate minimizing the number

of firings to which the casting is

subjected.


Removing the oxide layer



• Two principal methods for

removing oxides are

– Acid treatment (chemical method)

–Nonacid treatment (mechanical

method).www.indiandentalacademy.com

Acid treatment(chemical method)



• Different types of acids are used to reduceor eliminate surface oxides, including

hydrofluoric, hydrochloric, and dilute

sulfuric acid.

• The potential hazards of these acids

require that they be stored and used in

clearly marked, resealable plastics bottles.

• It is advisable to wear protective rubber

gloves and eye protection during all

handling procedures.www.indiandentalacademy.com

• A rubber-tipped instrument should beused to place oxidized castings into

the acid appropriate for the alloy.



the acid appropriate for the alloy.

• Place the covered container in anultrasonic unit for the time

recommended by the alloy

manufacturer.

• Remove the casting and thoroughly

rinse it under tap water. For the finalcleaning step, put the coping in a

container of distilled water and clean

it lt i ll f 10 t 15 i twww.indiandentalacademy.com

Nonacid treatment(Mechanical method)



• Castings can be air-abraded with pure, 50-um aluminum oxide (Al2o3) that is non-

recycled.

• Steam clean or ultrasonically clean thecasting in distilled water for 10 to 15

minutes before applying the opaque

porcelain.


Porcelain-metal bond failures



• Metal ceramic alloys, whether nobleor base metals, all oxidize differently

because of variations in their

composition.• If the oxidation process is not

performed properly, the subsequent

porcelain-metal bond may be weakand may lead to bond failure.





Porcelain delamination

With b t l ll th



• With base metal alloys, the

separation of the porcelain veneer

from the metal substrate can be

more a loss of the "attachment" ofthe oxide layer that is either too

thick or is poorly adherent to the

metal substructure.





Porcelain delamination contd



• Overoxidation has been a particularproblem with the heavily oxidizing

base metal alloys and has been

linked to their increased tendency forbond failures .


• Bond failures are not caused by a lossof the chemical bond between the



ceramic and the oxide layer• on the contrary, the porcelain might

remain visibly attached to the oxides

but the oxide layer may be so thick thatthe bond is lost through it .

• This particular problem is caused by

the formation of a thick and poorlyadherent oxide layer.





Classification of bond failures inmetal-ceramics.



• (Given by O‘ Brien (1977). • 1) Metal – Porcelain:

• Fracture leaves a clean surface of

metal. Seen when metal surface is devoidof oxides. May also be due to

contaminated or porous metal surface.

Usually occurs in high gold alloys.


• 2) Metal oxide – Porcelain:

• Porcelain fractures at metal oxide

surface leaving oxide firmly attached to



surface, leaving oxide firmly attached to

metal .Seen more often in base metal alloysystems.

• 3) Metal – Metal Oxide:

• Metal oxide breaks away from themetal and is left attached to the porcelain.

Seen commonly in base metal alloy

systems due to over production ofchromium and nickel oxides.


• 4) Metal Oxide –Metal Oxide:

• Fracture occurs through the metal

oxide Results from overproduction of



oxide. Results from overproduction of

oxide causing sandwich effect between

metal and porcelain. Occurs during the

usage of nickel-chromium alloys.

• 5) Cohesive within Metal:

• More common in bridges where the

joint area breaks. Rarely seen in single

crowns.


• 6) Cohesive within Porcelain:



6) Cohesive within Porcelain:

• Tensile failure within porcelain. Bond

strength exceeds strength of porcelain.

Seen in high gold content alloys.


• Excessive

absorption of



oxides by theporcelain can lower

the porcelain's

coefficient of

thermal expansion,

alter the final

shade (cause a

graying or bluing),or do both (Naylor,

1986www.indiandentalacademy.com

• Changes in theshade of the

porcelain may



not be noticeablewith posterior

restorations,

particularly if agreater thickness

of porcelain

masks the darkoxides


Incompatible materials• Further more, bond failures are not always

attributable to improper oxidation but may



attributable to improper oxidation but may

actually be caused by a physical

incompatibility between the porcelain and

the metal substructure. The difference in

the coefficient of thermal expansion of theveneering porcelain and the metal ceramic

alloy may be slight yet sufficient to be

responsible for cracking of the ceramicveneer or substantial enough to result in

porcelain debonding.www.indiandentalacademy.com




Overoxidation/underoxidation

• The oxidation procedure varies for alloys



p y

of different compositions.• Careful processing followed by an

assessment of the postoxidation

appearance of each casting will ensurethat the procedure was accomplishedcorrectly.

• Castings that are either overoxidized or

underoxidized should be reprocessedaccordingly until a uniform oxide of thedesired color and thickness recommendedfor the alloy involved has formed.www.indiandentalacademy.com

• Contamination



–castings that demonstrate some formof contamination may not have to beremade but by simply refinishing a

substructure's porcelain-bearingsurface may be all that is necessarywhen surface debonding becomesevident. Uncontaminated finishingmaterials are used to prevent this.





• Simply

refinishing this



casting removedthe surface and

subsurface

contaminationand resulted in

an appropriate

porcelain-metalbond.


Applying Porcelain to the MetalSubstructure



• The application of dental porcelain to

the metal substructure is the single

most demanding procedure in the

fabrication of a metal ceramic

restoration.

• As a rule, the skills needed for thisparticular process require the most

effort to perfect.www.indiandentalacademy.com

Instruments and equipment

• Brushes



• A variety of brush sizes and styles areavailable in porcelain instrument kits, themost important of which are the brushesused for building or stacking porcelain.

. The size range varies from a no. 4 to a no. 8.Sable brushes are the standard becausethey permit easy manipulation of the

porcelain.


• Another frequently used instrument is a

large no.10 brush, often referred to as a



g ,

whipping brush

• A basic instrument kit should also include

flat brushes with relatively stiff bristles.

These large- and small-sized brushesshould be kept dry because they are used

exclusively to remove porcelain particles

from non porcelain-bearing areas and frominside the substructure prior to firing.


• Very small no. 0 to no. 000 sable

brushes are required for the



brushes are required for the

placement of stains or small

increments of porcelain. These

brushes are useful anywhere

maximum control is necessary


Carving Instruments• Porcelain carving instruments, designed for



shaping and carving porcelain buildups.• Carving instruments serve two principalfunctions.

• 1.Those with a serrated handle can beused to condense wet porcelain.

• 2.Instruments with blades, as well as thesmall discoid carver, can be used to build

(stack) porcelain, shape the buildup, andcarve the porcelain.


Spatula

• Small, flexible, metal spatula is used



p

to dispense and mix porcelain.• Any small metal fragments generated

during mixing can then be introduced

into the wet porcelain ascontaminants.




• This metal debris can dramatically discolorthe mix as well as the fired porcelain

restoration. With careful use, however, the

metal mixing spatula need not be abraded.

• But for added safety, a glass mixing rod is

often substituted for the metal spatula to

avoid this problem altogether.


Razor knives



• Another necessity in the basic set of

instruments is some type of razor knife,

equipped with a thin, flexible blade for

carving the porcelain buildup.


Hemostat• A small, straight or curved hemostat is

needed to hold the work during the



needed to hold the work during theopaquing process and during porcelainadditions and condensation.

• Hemostats can be modified to hold the

metal substructure securely withoutdamaging the metal margins. However, an18-gauge handle added to the lingual collarprovides a convenient, safe, yet secure gripfor removing the restoration from theworking cast and holding it duringcondensation


Glass or ceramic mixing slab



• Finally, either a glass slab, ceramic tile, orceramic tray can serve as a plate for

mixing and storing the porcelain during the

buildup procedure. Initially, a small mixing

slab will suffice (Fig 8-9a).




• As modifiers are added and morecomplex buildups are attempted,a larger

working surface will be required to

accommodate all the different porcelain

mixtures


PORCELAIN CONDENSATION.



• Condensing dental porcelain actuallyrefers to any procedure that results in the

unfired porcelain particles being tightly

packed on to themselves.

• As the particles moves closer together, the

air and moisture previously occupying the

space between the individual particles

move to the surface of the buildup.




• Any liquid or air that remains trapped inthe unfired porcelain will form voids in the

unfired ceramic.

• The presence of porosity in fired porcelainweakens the restoration and impairs its

esthetic qualities.




Capillary action.



• The technique of blotting a wetbuilt up with absorbent paper

uses surface tension.


Vibration.



• Is created by passing a serratedinstrument over the neck of a

hemostat in which the restoration is

held.• Vibration is a means to mechanically

draw additional moisture to the

surface where it can then be removedby blotting paper.


Spatulation.



• A spatula is used to apply ,then rub the porcelain built up

to force the liquid to the

surface.


Whipping.



• A no. 10 sable brush is rapidlymoved over the porcelain surface

with a whipping motion. The

whipping motion brings the liquidto the outer surface for blotting.


Dry powder addition.



• Requires dry porcelain powder besprinkled on an area of wet

porcelain, using the existing liquid

to moisten the powder addition.


Opaquing the metalsubstructure



• The areas of the substructure that willbe veneered with porcelain must notbe touched and should be protected

from dust, oils from the skin, and anyother forms of contamination





Applying opaque porcelain—

glass rod technique



• First wet the oxidized metal substructure

to be veneered with distilled water and

gently vibrate the casting to thoroughly wetthe surface.

• A wet surface makes porcelain application

easier and reduces the possibility of

trapping air between the porcelain and the

metal. The thin film of water also will draw

the opaque particles onto the metalwww.indiandentalacademy.com




Glass rod technique.



• Use the pointed end of the glass rod to

apply the opaque porcelain. Begin by

opaquing the most convex portion of the

coping Move the opaque toward theporcelain-metal junction from one

interproximal area to the other and

cover the incisal edge.




• Then move the opaque over the incisaledge to cover the porcelain-bearing

surface on the lingual aspect. Once the

porcelain-bearing areas are completely

covered, lightly tap the hemostat and the

porcelain will settle into any concavities




• If, during the opaque application,areas of opaque appear rough andirregular, lightly tap the hemostat



handle or move the serrations on acarver across the hemostat in asawing motion.

• The vibrations created by either ofthese procedures will act tocondense the wet porcelain into a

more uniform layer.•




• Excess moisture should be removedbefore the opaque is applied to the metal.

Gently blend the opaque at the porcelain-

metal junction.

• Lightly tap the hemostat and dry the

opaque by placing it in front of an open

porcelain furnace muffle.





• Dry the opaque layer



y p q y

by exposing it to the

heat radiating from

the porcelain muffle.




• A properly fired(sintered)

opaque layer

should have asheen or

eggshell glisten.


• If a second application of opaque

porcelain is required, lightly wet the



opaqued surface with opaque liquid.• Apply the second opaque porcelain

layer in the same manner as the first.

• Keep this second layer as thin anduniform as possible.





Applying opaque porcelain—brush technique



• Simply mix theopaque porcelain

.Use the tip of

porcelain brush to lift

a portion of the mixed

opaque


• Apply the porcelain on the most

convex part of the oxidized coping.

R h l i



Repeat the process several timesuntil the porcelain-bearing area is

completely covered with porcelain.





Mixing dentin porcelains

f



–The technique for mixing body

porcelains is same as that used

to mix opaque porcelains in that a

glass rod is preferred to a metal

spatula and the liquid is carefully

added to the powder to prevent

the entrapment of air.


• Mix the body

powders (dentin

d l) ith



and enamel) with

the

recommended

liquid (Vita VMK

68 porcelain and

modeling liquid )


Wh l



• When properlymixed, dentin

porcelain should

have asmooth,cream

consistency.


If t h li id i



• If too much liquid isadded to the mix,

use a tissue or

blotting paper to

remove excessliquid until the

proper consistency

is achieved.


Appling dentin porcelain.

Th d ti l i b ild



• The dentin porcelain buildupprocedure is to apply and condense

enough porcelain to create a

restoration that is 10% to 15% largethan normal.


• This overbuilding will accommodate

the enamel veneer that will be placed



over the dentin layer and help to

compensate for shrinkage of the

porcelain. A high quality sable brush

is preferred to create the porcelain

buildup


The dentin built up technique.

R t th



• Return thecleaned,

opaqued coping

to the mastercast.


• To minimize theentrapment of air in

the porcelain,

th ti f th



move the tip of thepointed brush

through the mixed

dentin porcelainand remove the

brush with the

dentin porcelain

captured on the

brush


• Apply the

porcelain to the

t



most convexsurface (midfacial

area) on the

restoration.


• Coax the porcelain

toward the

interproximal and

incisal areas Add



incisal areas. Addmore porcelain to

the facial surface

and use a lighttapping motion to

move the porcelain

along theporcelain-metal

junction.www.indiandentalacademy.com

• Move the porcelaindown to the incisal

edge and lightly blot

the buildup to

condense the



condense theporcelain on the

substructure. place

the additional dentin

porcelain in the incisal

region and move it

from one

interproximal area tothe other.


• Control the flow ofthe material and

condense the

buildup by



buildup byperiodically blotting

the wet porcelain

with the tissue. use

light gingival-to-

incisal strokes on

the facial surface

to create thedesired facial

contour.www.indiandentalacademy.com

Add additional



• Add additionalporcelain to the

incisal aspect of

the incisal edge.


Add additional



• Add additionalporcelain to

complete the

mesial and distalcorners.


Cutting back the dentin buildup

• With the buildup complete, dentin

l i t b d f th



porcelain as to be removed from those

areas of the crown where you would like to

have enamel porcelain. The procedure of

removing dentin porcelain for enamelplacement is referred to as the "dentin

cutback."


If dentin porcelain is overbuilt(A), the amount ofdentin remaining after the cutback may also be

incorrect.




When the restoration has the correctanatomical contours and is slightly

overbuilt(A) by 10% to 15%, the dentin

cutback will also be correct



cutback will also be correct.




• Remove dentin

l i t th



porcelain at the

mesial

interproximal line

angle. Extend thecut to the junction

of the middle and

gingival one thirdsfor younger

patients.www.indiandentalacademy.com

• Cut across the



• Cut across themiddle one third.

Stop the cut

back at the distalinterproximal

area.


• At the distal

interproximal line

angle, make a cut

from the incisal edge



from the incisal edgetoward the gingival

one third as far as

required for the

esthetics .Then cutback the middle one

third of the facial

surface as necessary.


• Examine thei f



• Examine therestoration from

an incisal view

for symmetryand adequacy of

the cutback.


• Smooth thetb k



• Smooth thecutback areas

with the

porcelain brushso the transitions

from dentin to

enamel porcelainare gradual.


• For younger

patients develop



patients ,developmamelons.With a

pointed brush

,create twodepressions on the

facial surface with

vertical strokes

from incisal to

gingival.www.indiandentalacademy.com

Mixing the enamel

porcelain



porcelain.


• Glass rod is used

to mix the powder

and liquid .The

enamel mix is



enamel mix isslightly wetter than

the dentin mix to

facilitate itsaddition to a

previously applied

and condenseddentin layer.


• The mixed enamel

porcelain should have



porcelain should have

a consistency that

permits it to be readily

picked up by aproperly pointed

porcelain brush.


• With a pointedb h l



• With a pointedbrush, apply

enamel porcelain

to one corner ofthe cutback.


• Add more enamelporcelain andmove it across the

facial surface in thei i l thi d



facial surface in theincisal one third.Push the wet mixtoward the middle

one third of thecrown and work itinto the oppositeinterproximal lineangle.


• Blend the enamelporcelain at the

junction of the

middle and gingival



middle and gingivalone thirds and

begin to establish

the incisal edgeand condense the

porcelain by

blotting

periodically.


• With additional

enamel porcelain,

complete theincisal edge length



complete theincisal edge length

and the mesial-

incisal line angle.

Work your wayalong the incisal

edge to create

more of a distal-incisal line angle.


• Blend the enamel

porcelain into the

gingival one third



gingival one thirdon the facial

surface. Re-create

the interproximalcontours and line

angles.


• Shape the mesial-incisal corner as

required for each

case Examine the



case. Examine thebuiltup from an

incisal view and

evaluate theoverall shape.

Make certain the

restoration is

slightly over built.


• Condense the built

up



up.


• Use your thin razorknife to cut and

shape the mesial

and distalinterproximal



and distalinterproximal

areas. This

procedure also

removes any

unwanted

porcelain below the

interproximalcontact areas.


• Carefully remove

the crown from the



the crown from the

master cast. Add

enamel porcelain

to the smalldimples in each

interproximal

contact area.


• Remove excess

porcelain from the



pporcelain-metal

junction and clean the

facial metal collar of

any porcelain with a

small brush or your

pointed porcelain

buildup brush.


Firing procedure.

• The large bulk need more time to dry and

pre-heat



pre heat.

• Adhere to manufacturers recommended

drying time.

• A properly fired porcelain body bake

should have a pebbly or ―orange peel

appearance‖.


Adjusting and finishing the metalceramic restoration.

• Applying and firing the porcelain veneer to

a metal substructure only approximates



a metal substructure only approximates

the shape, contour, occlusion, and surface

finish restoration.

• The porcelain application process requires

slight overbuild of the ceramic, this results

in a bulky restoration.


• Consequently, the fired porcelain requires

additional adjustments to reduce any

overcontouring and recreate a lifelike

ceramic surface finish before the



ceramic surface finish before thecharacterizing (staining) and glazing

stages.

• Adjusting , contouring, and finishingprocedures for metal ceramic restorations

play a critical role in achieving both proper

function and optimal esthetics.


Armamentarium.

• 1. Equipment – Handpiece with speeds of

50 000 rpm or below



50,000 rpm or below.

• 2. Instruments – Iwanson metal caliper.

• 3. Materials – Diamond abrasives,

Prepolish wheels, diamond disks.


• The iwansonmetal calipers



The iwansonmetal calipers

can be used for

thicknessmeasurements

of metal or metal

and porcelain.


• Diamond abrasive

instruments



instruments.


• Porcelain

prepolish wheel



prepolish wheel

.Designed for

smoothening andpolishing

ceramic

surfaces.


• Diamond disks

For adj sting



• For adjusting

and contouring

interproximalareas.


Procedures in adjusting and

finishing the metal ceramic

restoration.

• 1. To ensure the



1. To ensure the

casting

completely seats

on the die.


2.Adjusting the interproximal contacts.

• a) Mark the

mesial



mesial

interproximal

contact usingthin double –

sided marking

film.


• b) Marking

identifies the



identifies the

location and

intensity ofcontact.


• Adjustments in

the contact area



the contact area

with pre-polish

wheel.


• The thickness of

the restoration is



the restoration is

periodically

checked toensure that it is

not over

contoured.


• The desired

characterization

is marked andwith an



with an

abrasive the

appropriateshape is

created with

desired effect.


Staining and glazing.

• After a restoration has been adjusted and

finished, it is necessary to make color



, y

corrections or additions and create a

lifelike surface luster.




• Stain is placedin area where

the

characterizationis intended.



is intended.

Blend or dilute

the effect of the

stain


• The glaze ispicked up with

a staining

brush and



applied to the

ceramic

surface wheredesired.


• Dry the

restoration in the



restoration in the

porcelain

furnace.


• The restoration is

fired according to thel i



porcelain

manufacturers

direction.


• Typicallyglazed



yp yglazed

restoration.


Mechanical polishing.

• Mechanical polishing of thet ti ft l i i th



p grestoration after glazing gives the

restoration a natural life like

appearance.




A diamond polishingpaste.

Pumice flour


• Aftermechanical

polishing. A

life like luster



is created in

the ceramic

yet the surfacecharacterizatio

n remains.


Porcelains Used in Metal Ceramics / orthodontic courses by Indian dental academy

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