Ceramics

Ceramic

Inorganic, nonmetallic, solid - generally based on oxide, nitride, boride. or carbide at high temperature

Glazed prior to firing to produce a coating that reduces porosity and has a smooth, colored surface

Ionic with covalent bonds

Glazing of Ceramics

Prior to firing to produce a coating that reduces prorosity and has a smooth, colored surface

Ceramic Bonds`

Ionic bonds are strong and directional

Do not tolerate bending

Properties of Ceramics

Biocompatible

Chemically inert

Low thermal diffusivity

Excellent wear resistance

Good esthetics

High modulus of elasticity

Good resistance to compressive stress

Brittle

Low fracture toughness and low tensile strength

High melting point

Microstructural Classification

At the microstructural level

Based on glass to crystalline ratio

Category 1 Ceramic

Glass based system

Composition Category 2

Glass based systems with fillers that are usually crystalline

Composition Category 3

Crystalline based system with glass filler

Composition Category 4

Polycrystalline solids

Silica Tetrahedron

Basic building block of silicate minerals

Composed of one silica ion surrounded by four O2

Link up in various patterns and bond with metal ions to form specific silicate minerals

Quartz

Crystaline - SiO2

Glass Structure

Amorphous - occurs by adding impurities to silica tetrahedron

Impurities - interfere with formation of crystalline structure (Na+, Mg2+, Ca2+, Al3+)

Feldspathic Ceramics

Veneers

Si-O-Si network

Modifying cations

Low strength with high translucency

Properties typical of glass

Crystalline phase - leucite - K(AlSi2O6)

Provides strength

Feldspathic Porcelain

Kaolin - quartz - feldspar

Proportioned and fired at high temperature

Incongruent Melting

Makes feldspar into two phases

Crystalline leucite

Glassy phase

Non-uniform

Leucite Re-Informed Ceramic

Potassium aluminium silicate mineral in crystalline form

~50% glass

Increases strength of ceramic

Lithium Dislicate Ceramics (E-Max)

70% crystals that are embedded in glassy matrix

Cause cracks to deflect

Increase flexural strength

3x leucite fracture toughness

Superior translucency due to compatibility between glassy and crystalline phase

IN-Ceram Alumina

High strength with poor translucency

Add glass to crystalline structure

IN-Ceram Spinell

Thermal and electrical insulation, low value appearance

IN-Ceram Zirconia

Aluminum oxide with tetragonal zirconium oxide

Very high strength

High poor translucency

Sintering

Heating ceramic to a point where the ceramic particles begin to fuse with

Start with ceramic powder mixed with water (green state)

Ground porcelain (green state) is heated

Temperature is called fusion temperature

Particles melt and fuse at their surface

Shrinkage occurs

Cooled particles form the ceramic

PFM (Metal-Ceramic Restoration)

Esthetics of ceramics + mechanical properties of metals

Stacking

Used primarily for glassy and glass dominated ceramics

Used to apply ceramics to alloys or high strength ceramic substructures, or to fabricate laminate veneers

Viscous slurry of the porcelain particles in water or water-glycerol is applied to a substructure, using vibration to pack the particles and expel the liquid to the surface

Pressing

Used to force a viscous mass of molten ceramic into a mold to get the desired final form

Process similar to casting - ceramic forced into mold under pressure

Often employed today for making all-ceramic cores from glass-dominated or crystalline dominated ceramics

Tetragonal Zirconia

1200 < T < 2370 degrees celsius

Most stable, strong, and opaque form of zirconia

Yttria

Stabilized zirconia in the tetragonal phase

Advantages of Zirconia

High strength

Adequate esthetics

Conservative tooth prep

Less time for tooth to be (-) influenced by temporary

Disadvantages of Zirconia

Compromise in high level esthetics

Difficult to remove

Need to polish after adjustment

Stress Concentration

Small flaws, defects, sharp line angles

On intraoral loading - cause tensile stress to concentrate at tips of the flaws

Stresses are greatly increased, causes bonds to break and cracks to form and grow