Ceramic

CERAMIC Dental Materials

DEFINITIONS

• Ceramic –• An inorganic compound w/ non metallic properties

typically composed of metallic and non metallic elements

• Dental ceramic – • An inorganic compound w/ non metallic properties

typically composed of O2 and 1 or more metallic or semi metallic elements that is formulated to produce the whole part of a ceramic based dental prosthesis

4 categories of ceramics

1. Silicate Ceramics2. Oxide Ceramics3. Nonoxide Ceramics4. Glass Ceramics

Silicate Ceramics

• Amorphous glass phase with a porous structure• Main components:• SiO2• Small quantities of :• Al2O3• MgO• ZrO2

Dental porcelain

Oxide Ceramics

• Principally contains: • Al2O3,MgO,ZrO2 with either no glass phase or

small content.

Non oxide Ceramics

• Impractical for dental use• Why?• High sintering temp• Unesthetic color• opacity

Glass Ceramics

• Are partially crystallized glass• Produced by nucleation and growth of crystals

in glass matrix phase

Dental ceramics

• May consist primarily of :• Glasses , glass ceramics or highly crystalline

structures• Ceramics are more resistant to corrosion than plastic• Remain stable for a long period of time• Do not react with most liquids, gases • Excellent – fair fracture toughness• Zirconium dioxide > Flexural strength similar to steel

Dental ceramics

• Biocompatible• Long term color stabbility• Wear resistance• Ability to be formed into precise shapes

CLASSIFICATION OF DENTAL CERAMICS

Phillips Dental Materials

Dental ceramics can be classified according to :

• Use or Indication- Anterior- Posterior- Crowns- Veneers- Post and cores- FPDs- Stain ceramics- Glaze ceramics

• Composition- Pure alumina- Pure zirconia- Silica glass- Leucite-based glass ceramic- Lithia based glass ceramic

• Processing method- Sintering- Partial sintering- Glass infiltration- CAD CAM- Copy milling

• Firing temperature- Low fusing- Medium fusing- High fusing

• Microstructure- Glass- Crystalline- Crystal containing glass

• Translucency- Opaque - Tranlucent- transparent

• Fracture Resistance

• Abrasiveness

Metal Ceramic Prosthesis

• COMPOSITION OF DENTAL PORCELAINS• Most dental porcelains consist of • Kaolin• Silica• Feldspar• Glasses

Glass modifiers

• Manufacturers employ glass modifiers to produce dental porcelains with different firing temperatures

Categories Firing temperatureHigh fusing 1300oC or aboveMedium fusing 1101 to 1300oCLow fusing 850 to 1100oCUltra low fusing < 850oC

Feldspathic Porcelains

• Feldspar- main ingredient of classical metal ceramic porcelain. ( crystalline and opaque)

• Chemically designated as K2O.Al2O3.6SiO2

• These ceramics are called porcelains because they contain a glass matrix and one or more crystal phases.

Other Additives

• B2O3 ( Boric Acid) – behaves like a glass modifier• Alumina – not a true glass modifier but can alter

softening temperature and viscosity• Pigmenting oxides – natural shade of tooth• Iron or nickel oxide – brown• Copper oxide – green• Titanium dioxide – yellowish brown• Manganese oxide – lavander• Cobalt oxide – blue• Opacity– zirconium oxide, tin oxide

Esthetic potetial

Metal ceramic• 70% of all fixed restorations• Not the best esthetic choice• Dark line at facial margin

All Ceramic• Matches appearance of

adjacent natural tooth• More susceptible to

fracture• Ceramic margin

Porcelain Condensation

• Supplied as a fine powder to be mixed with water or another vehicle and condensed into desired form

• Dense packing has 2 benefits:1. Lower firing range2. Less porosity• Packing may be achieved through1. Vibration2. Spatulation3. Brush technique

Drying

• The restoration is placed in an open furnace to be dried.

• Until 480 deg C is reached• Drying stage – 5- 8 minutes• Ensures the remaining water is removed• Dries too quickly – spontaneous breakage • If wet structure is placed onto firing in hot

furnace – steam-crumble-explode

Sintering of porcelain

• The purpose of firing :• To sinter the particles of powder together

properly to form the prosthesis.• Sintering – process of heating closely packed

particles to a specified temp to densify and strengthen a structure

• After porcelain is preheated, firing cycle is initiated.

Overglazing and shading

• Natural glazed porcelain is much stronger than ground, rough, non glazed porcelain.

• Glaze – effective in reducing crack propagation within the outer surface.

• Stains and glazes

Cooling of metal-ceramic prosthesis

• Sudden changes in temperature – fracture• Slow cooling followed by slow opening of

furnace door

Benefits and drawbacks of metla ceramics

• Stronger and more durable than all ceramic crowns

• Permanent aesthetic quality• Fracture resistance• No abrasion wear• No staining along metal and veneer interface• Less tooth structure is removed to provide

proper bulk for the crown.

Ceramics for Ceramic Metal Restorations

• 5 requirements:1. Must simulate appearance of tooth2. Fuse at low temp3. Must have compatible thermal expansion

with metals4. Must withstand oral environment5. Must not abrade opposing teeth

Ceramics for ceramic metal restorations

• Ceramics are composed of crystalline phases in an amorphous , glassy vitreous matrix.

• Glass• They fuse at a lower temp , to prevent metal

from distorting

ALL CERAMIC PROSTHESIS

• Castable and machinable glass ceramics• Pressable glass ceramics• Slip cast All ceramic ceramics• Procera Allceram• CAD CAM ceramics

GENERAL APPLICATIONS OF CERAMICS IN DENTISTRY

• Ceramics are the best materials to match esthetic complexity of human teeth

• Used for ceramic metal crown• FPD• All ceramic resto• To fabricate denture teeth

Ceramic metal crowns

• ADVANTAGE:• Better abrasion resistance• More durable• Better adhesion with resin cements

• DISADVANTAGES:• Occlusal adjustment is more difficult• Not for high stress areas

All Ceramic Crowns, inlays , veneers

• Ceramic veneer – layer of ceramic bonded to the facial surface of a prepared tooth to cover any defaults.

• Custom made , fabricated in lab.