Dental Ceramics

Dental ceramics: Greek word kermikos : burn stuff Which means that the desirable properties of these materials gained by firing at high temperatures

Compounds formed of metallic and non-metallic elements Includes: Oxides Nitrides Silicates

General properties: They have high melting temperature. They are heat and electrical insulators: therefore they are used as refractory materials. The are characterized by their transparency due to lack free electrons interacting with incident light. However porosity introduced during fabrication makes them appear translucent at least in thin sections.

General properties: Mechanical properties: Strong ionic and covalent bond. Low tensile strength as it brittle materials.. Low fracture toughness. Hard.

General properties: Chemically inert in the oral environment due to: They are formed by oxidation therefore they cannot react further. They are strongly bonded so it doesn't leach out any of its components in the oral cavity. Chemically indestructible; to be dissolved strong acids such as HF acid can be used.

Dental porcelain

Introduction Dental porcelain is of the ceramic materials. It is a glass phase from high purity feldspar, and crystalline phase of quartz fine ceramic powder that can be mixed with water to form a paste. The paste is formed into the desired shape, and fused at a high temperature

Uses: Denture teeth Jacket crown Porcelain metal crown and bridge work. Simple inlays, onlays and veneers.

Advantages High aesthetic. High color salability & compatiblability. Resist sudden thermal changes. Adequate strength.

Disadvantages: No exact matching color and texture of the teeth Involves removal of additional tooth structure. Excessive wear of the teeth in the opposing arch.

Composition: Feldspars Silica Kaolin Other ingredients Glass modifiers Fluxes Coloring pigments Sugar and starch Fluorescent agent

Composition 1-Feldspars: 80% They are anhydrated aluminum silicate; they are mixtures of: K2O, Al2O3, 6SiO2 orthoclase Na2O, Al2O36SiO2 albite.

Composition 1-Feldspars: 80% Function: Act as flux binds other ingredients retains the form of porcelain restoration during firing.

Composition: 2-Silica 15% (quartz): It remains unchanged during the firing process Function: acts as a strengthening agent. It is present as fine crystalline dispersion throughout the glassy phase.

Composition: 3-Kaolin 4% in decorative porcelains only: Kaolin is hydrated aluminium silicate Al2O3.2SiO2.2H2o It gives the opaque property to the porcelain. Modern dental porcelain dose not contain kaolin.

Composition: 3-Kaolin 4%: Function: Acts as a binder Increases the mouldability of unfired porcelain to form workable mass of the porcelain.

4-Other ingredients A- Glass modifiers: Metal ions as Na+, K+ or Ca+2 produce dental porcelains with different firing temperatures Effect of glass modifiers: Increase fluidity of the glass. Lower softening temperature. Increased thermal expansion.

4- other ingredients: B- Fluxes: (low fusing glasses) are often added to reduce the firing temperature C- Coloring pigments: They give the required color e.g. metal oxides.

4- other ingredients: D- Sugar & starch: They help in the powder manipulation. E- Fluorescent agent: Lanthanide oxide is used to provide fluorescence instead of uranium oxide which has a small amount of radiation.

Manufacture: All components are blended together, melted, and the quenched while red hot to break up into frits. Pyrochemical reaction: at high temperature fluxes combine with silica.

Manufacture: Phases present: 1- Vitreous phase or glass phase: during firing. 2- Crystalline phase or mineral phase: silica, leucite and metallic oxides.

Manipulation: porcelain is made from a number of powders, because of the aesthetic features of teeth Types of porcelain powder: Opaque shade Dentin shade Enamel shade

The production of porcelain stages: Compaction Firing Glazing Cooling

Production: 1- compaction Powder of dentin color mixed with distilled water to a creamy consistency and applied to the desired form. In over-size to compensate for shrinkage.

Production: 1- compaction condensation Vibration Spatulation Using dry powder

Production: 1- compaction condensation Vibration: Mild vibration to pack the wet powder. Excess water is plotted using clean tissue.

Production: 1- compaction condensation Spatulation: small spatula is used to apply and smooth the wet powder. Excess water derived to the surface then removed

Production: 1- compaction condensation Dry powder: Addition of dry powder to the surface and it will be absorbed by the wet mix. water is drawn toward the dry powder the wet powder are pulled together.

Production: 2- firing: In electric oven with pyrometer to sinter the particles of the powder. Firing can be done in open air or under vacuum.

Production: 2- firing: During firing : Loss of water Temperature raise Sintering

During firing and sintering Low bisque stage: fluxes start of flow Medium bisque stage: water evaporate and shrinkage occurs High bisque stage: fusion between particles to form a continuous mass.

Production: 3-Glazing: Produce smooth shiny surface, fill up the cracks and improve the strength.

Production: 3-Glazing: Types: Self glaze: Flow of the glass at the surface of the restoration. Low fusing glass: Added to the surface of the restoration

Production: 4-Cooling : Slow to avoid crazing.

Classification: According to fusion temperature: Repair Denture teeth High fusing 1300OC Medium fusing 1100-1300OC Denture teeth Low fusing 850-1100OC Crown and bridge <850OC Crown and bridge Ultra low fusing

Properties: 1-Shrinkage: More water more the voids after firing 2-Porosity : Internal voids affect the translucency and strength Vacuum and cooling under pressure reduce porosity.

Properties: 3-Chemical properties: It is chemically indestructible. Except for (HF). 4-Mechanical properties: Brittle material High hardness number

Properties: 5-Aesthetics and color: Excellent but not perfect. Can match colors and shades of natural teeth. 6-Biological effect: Very inert and no adverse tissue reaction.

Porcelain teeth High and medium fusing porcelain. Packed into metal molds and fired Retained in denture base by mechanical interlocking.

Porcelain teeth Advantages: More aesthetic More resistant to wear Allow for rebasing

Disadvantages: Brittle Produce clicking sound Require greater inter-ridge distance High density than acrylic Low α than the base cause crazing Very hard difficult to finish and polish Non resilient transmit more stresses to the underlying bone.