Dental Ceramics | Dental Porcelains Composition and Classification

Ceramics or Porcelains are chemically intimate mixtures of metallic and non metallic elements, that allow ionic (K2O) and/or covalent bonding (SiO2) to occur.

The most common ceramics used in dentistry are alloys of 3 main metallic oxides (SiO2, Al2O3, K2O).

Composition of Dental Ceramics and Dental Porcelain:

1) Feldspar: 60 to 80%. this is a mixture of Sodium Aluminium Silicate. Na2O.Al2O3.6SiO2 (Albite) and potassium aluminum Silicate K2O.Al2O3.6SiO2.

Use: Reduces Firing (fusing) temperatures and increases the viscosity of the molten glass

These when melted (at 1250 – 1500 C) combines to form a glass with a free crystalline silica phase. Fusion temperature is lower if  Na2O/K2O ratio is less.

2) Quartz (or) Silica: 15%to 25%. Used in Porcelain as a strengther. It remains unchanged during firing.Forms of Silica are Quartz, Cristobalite and tridymite. It is a a very hard, infusable and stable compound.

3) Kaolin (Al2O3.2SiO2.2H2O): 3 to 45%. This is a variety of Clayacts as flux and a binder, gives opacity to the mass. Increases the mouldability of the unfired porcelain.

Use: Acts as a Flux

4) Alumina: 8 to 20%. Only in Aluminous Porcelain. Due to Brittleness it can easily be powdered to very fine particles.

5) Opacifiers: Zirconium, tin or titanium oxides – small quantity

6) Metallic pigments: Less than 1%

7) Zinc Oxide(ZnO), Silicon Carbide(SiC):  Used in Dental cements, and as Abrasive and Polishing agent.

Classification of Ceramics:

1) According to their Application:

• Artificial Teeth
• Jacket Crown and inlayss
• Enamel Veneer over cast metal crown
• Abrasive and Polishing agents

2) According to their maturing or Fusion Temperature:

• Low Fusing 871 to 1066 C
• Medium Fusing 1093 to 1260 C
• High Fusing 1288 to 1371 C

3) According to their types:

• Felspathic or Conventional porcelain
• Leucite – reinforced porcelain
• Aluminious Porcelain
• Glass – infiltrated alumina
• Glass Ceramic

4) According to their Substructure Method:

• Cast metal
• Swaged metal
• Glass Ceramic
• CAD-CAM porcelain
• Sintered Ceramic core

5) According to their Method of Firing:

• Air fired at atmospheric pressure
• Vacuum fired at reduced pressure