1Metal ceramicsPRESENTATION BYGUIDED BYDR. B.SAI KUMAR DR. ANAM CHANDRASEKAR

2contents

• Definition:• Introduction:• Terminologies:• Components:• Tooth preparation:• Alloys:• Metal ceramic substructure:• Metal ceramic bonding:• Steps in fabrication:• Advancements:• Conclusion:• References:

3Definition:

• Metal Ceramic Restoration: A tooth or/and implant retained fixed dental prosthesis that uses a metal substructure upon which a ceramic veneer is fused.(GPT-8)

4Terminologies:

• PFM: porcelain fused to metal

• PVC: porcelain veneer crown

• PBM: porcelain bonded to metal

• Ceramo metal crown

5components

• Metal substructure

• Oxide layer

• Opaque porcelain

• Dentin veneer

• Enamel veneer

• Surface glaze

Thickness of Metal Supported Porcelain CrownsMetal Coping:

Noble metal: 0.5mmBase Metal: 0.3mmOpaque Porcelain: 0.2mmEnamel+Dentine 0.8-1 mmTotalFor noble Metal:1.5 mmFor base metal: 1.3 mm

6

7Tooth preparation for metal ceramic restorations:

FACIAL MARGIN1. DEEP CHAMFER2. SHOULDER WITH BEVEL3. SHOULDER4. RADIAL SHOULDER

8Alloys for metal ceramics:

IDEAL REQUIREMENTS:

• Able to form oxides

• CTE > ceramic

• Melting temp > ceramic

• Sag resistance

• Bio compatible

• Ease of handling

9Classification of alloys:

10Gold-platinum-palladium system:

11Gold-palladium-silver system:

High silver Low silver

12Gold-palladium system:

13Palladium – silver system:

14High palladium systems:

cobalt copper silver

15Nickel-chromium alloy:

Beryllium Beryllium free

16Cobalt-chromium alloy:

17Metalceramic substructure

Primary functions:

Marginal fit

Chemical bond

Rigid foundation

Restores tooth emergence profile

Secondary functions:

Metal articulating surface good for opposing enamel

Easily adjusted and polished intraorally

Can support components of rpd

Can house attachments

Less tooth reduction

18Fundamentals of metal substructure:

• Begin with accurate full contour waxup

• Contact 1.5-2mm away from metal porcelain junction

• No max thickness of metal

• All surfaces smooth with rounded convex contour

• Uniform thickness of porcelain, not >2mm

• Porcelain metal junction

19opaque porcelain

8-15% metal oxides, 5microns in size.

Functions:• Establishes metal to porcelain bond

• Masks the color of metal

• Initiates development of shade

20Mechanism of porcelain metal attachment

1. Vanderwaal forces

2. Mechanical retention

3. Compression bonding

4. Chemical bonding

21Chemical bond

22Oxidation process:

Air or vacuum firedTemperature 1100 degrees.

23Post oxidation treatment:

• Chemical – HF / H2SO4

• Mechanical – air abrasion

Methods of fabrication:

1. Condensing and Sintering,

2. Pressure molding & Sintering,

3. Casting & Ceramming,

4. Slip casting, Sintering & Glass infiltration

5. Milling (Machining) by mechanical and digital systems.

Steps in fabrication:

1. Condensation

2. Sintering

3. Glazing

4. cooling

Condensation:

• The process of bringing the particles closer and of removing the liquid binder is known as condensation.

• AIM : is to pack particles as close as possible,

reduce amount of porosity & shrinkage during firing

FACTORS DETERMING EFFECTIVENESS OF CONDENSATION:

1. Size of the particle2. Shape of the particle

• One sized particle = 45% void space

• Two sized particle = 25% void space

• Three sized particle = 22% void space - GAP GRADIENT SYSTEM

Round particles produce better packing compared with angular particles

Most important factor in condensation is effect of surface tension.

As the liquid is withdrawn , surface tension causes powder particles to pack closely together

Capillary actionVibration methodSpatulation methodDry brush techniqueWhiping method

Restoration E.g. Matrix used

All-ceramic PJC Platinum foil – adapted on the die to form

matrix

Metal ceramic PFM Metal coping of suitable design and alloy

type

• (For inlay / onlay restorations, ceramics are fired on refractory dies)

Mixing

• Dry porcelain powder is mixed with the binder on a glass slab using bone or nylon spatula (or glass mixing rod) into a thick creamy mix, which can be carried in small increments with an instrument or brush

Binder:

Binder – helps to hold the particles together

Types of binder used :

• Distilled water – most commonly used, especially for dentin / enamel porcelain,

• Propylene glycol – used in alumina core build-up,

• Alcohol or formaldehyde based liquids – used for opaque core build up,

• Proprietary modeling fluids

Arnamentarium:

The Vibration technique

• This method used mild vibration to pack the wet powder densely on the underlying framework.

• The excess water is blotted away with a clean tissue and condensation occurs towards the blotted area.

The Spatulation technique

• The method uses a small spatula to apply and smoothen the wet porcelain in incremental layers. The smoothing action brings the excess water to the surface where it is removed by blotting.

The brush technique

• It involves placement of dry powder onto the wet surface. The excess water moves from mixture to the dry powder by capillary action and wet particles are pulled together.

The whiping technique • A large soft brush is moved in a light dusting

action over the wet porcelain. This brings excess water to the surface, and the same brush can be used to remove any coarse surface particles along with the excess water.

Sintering

• Is defined as a process of heating closely packed particles to achieve interparticle bonding and sufficient diffusion to decrease the surface area or increase density of the structure.

36Application of opaque porcelain:

37

38Application of dentin porcelain

39Dentin cut back:

40

41Application of enamel porcelain

42

 Ceramic Furnaces :

• Two basic types of furnaces are:

• Horizontal Muffle e.g. : Vita-Caccumat “S”

• Vertical Muffle e.g.: De Try Biodent Systomat, Unitek Ultra-Mat Furnace, Rapid Cycle furnace (Doxc Euromat).

Different media can be employed for firing like

1. Air 2. Vacuum 3. Diffusible gas - He, H2 or steam

• During firing, the following changes are seen in the porcelain

Loss of water

Firing shrinkage - 32 –37% for low fusing

28 – 34% for high fusing

Glazing - 955 – 1065°C

• After the mass has been fired, it is cooled very slowly because rapid cooling might results in surface cracking and crazing

• Firing of dental porcelain consists of 3 stages of maturity.

• The common expression used for describing the surface appearance of un-glazed porcelain is “bisque” or biscuit since this gives a fairly accurate picture of its surface texture.

STAGES OF MATURITY

Low bisque Medium bisque High bisque

Characteristic feature

Grains start to soften & coalesce at contact points

Flow of glass grains increase & residual entrapped air becomes sphere shaped

Firing shrinkage complete & any correction by grinding prior to glazing.

Particle cohesion

Incomplete Considerable Complete

Porosity Highly porous Decreased but porous

Slight/absent

Shrinkage Minimal Majority/definite

High

Surface texture

Porous Still porous &matte surface

Smooth surface

Color & translucency

Opaque Less opaque & color developed

Color & translucencydeveloped

47Adjusting and finishing of metal ceramic restorations:

48Characterization:

Glazing

• At the end of high bisque stage, if the porcelain was held in the furnance for a greater length of time, the surface porcelain would undergo pyroplastic flow, i.e. the matter surface would disappear and a smooth shiny surface would result (SELF-GLAZE)

• Add-On Glazing – A low fusing transparent glass may be used as a glaze over the completed body of the porcelain restoration, and a short period at a relatively low temperature is sufficient to fuse the glaze.

50

Cooling

• Being poor conductors of heat and brittle in nature, whenever porcelain restorations are heated or cooled the process must be carried out slowly.

• Rapid cooling or sudden changes in temperature after firing of porcelain would result in cracking or fracture of glass and loss of strength.

• Eg. multiple firing of a metal-ceramic restoration can increase the coefficient of thermal contraction of porcelain and its likeliness to crack or craze because of development of tensile stresses.

Non cast metal ceramic systems

THE FOIL CROWN SYSTEMS

• Non-Cast Metal-Ceramic Systems are an advancement in the fabrication of metal-ceramic restorations, which permits the fabrication of a metal-ceramic restoration without waxing, investing or casting.

• Introduced by Dr. Itzhak Shoher and Aaron Whiteman in Europe, and subsequently in North America after many years of development.

• Foil Crown Technology represents a novel approach by which a metal ceramic crown can be produced in a relatively short time without melting and casting the metal.

• Types : Renaissance, Capatek, Ceplatec, Sunrise, Flexbond & Platideck.

Steps in fabrication:

• Initial adaptation

• Cutting the folds at the mid point.

• Folding pleats in same direction

• Burnishing the form for closer adaptation and

trimming excess metal

• Die spacing using strips of plastic sheet

• Swaging

• Alloying

• Application of interfacial alloy

• Firing (at 1000°C) to produce a sintered alloy surface

• Method - The pleated foil is swaged with a swaging instrument,

burnished with a hand instrument on the die, and then flame sintered

to form, a rigid coping, with moderate strength

• An interfacial alloy powder is applied and fired, the form is then

trimmed and veneered with porcelain (Condensation process) and

finally sintered

Captek system:

• This system bonding to porcelain is achieved by the formation of an intermediate layer of material such as Capbond metal-ceramic ‘bonder’ (bonding agent) for the Captek foil crown system. Two strips of highly malleable metal powder impregnated ‘wax’ are adapted to a refractory die. The first strip contains a gold, platinum and palladium alloy and the second is impregnated with all-gold.

• Ceplatec System

• (Keraplatin Dental, Wijhlen, FR, Germany) was reported as the same product as Renaissance, although the 2nd and 4Th layers are composed of Au, Pt, Pf, Ag & Ag, Pt, Ir; respectively. The latter layer is said to prevent warping during the heating procedure

Disadvantages of Foil Crown systems :

• Strength of metal-ceramic crowns was considerably higher than that of foil-based crowns (about 30 to 80% of the metal-ceramic systems).

62Conclusion:

Even with the advent of many advancements in ceramics, metal ceramics are in wide use because of its own advantages like minimal tooth reduction, acceptable aesthetics and cost effective long term solution.

63References:

• Philips science of dental materials{10th and 11th edition}• Esthetics of anterior fixed prosthodontics: chiche/Pinault• Esthetic dentistry: Dale Aschheim• Fundamentals of esthetics: Claude R Rufenacht

Rosenblum M.A., Schulman A. : A review of All-Ceramic Restorations. JADA, 128: 1997; 297-307.

• Anusavice K.J. : Recent Developments in Restorative Dental Ceramics. JADA 124: 1993; 72-84.

• Introduction to metal ceramic technology: naylor