Dental Materials · MU Sofia

39. Dental ceramics

Covers the history of dental porcelain and its raw minerals (feldspar, quartz and kaolin), with a table of each mineral's composition and role. Walks through how the powder is made from frit and which modifiers, colorants, luminophores and burn-off plasticizers it contains, then the layered build-up and the firing stages with temperatures. Ends with a table of mechanical properties for feldspar porcelain, followed by its aesthetic, surface, biological and wear advantages and drawbacks, and the main ways of making a restoration.

Inside: 6 sections · 2 labelled pictures · 2 tables · 14 flashcards · 3 min

Topic 39 of 52 in the MU Sofia syllabus for Dental Materials (Dental Medicine, Year 1). The free AceMed note covers it in 6 sections, about 341 words (3 min of reading), with 14 flashcards.

In this note

  1. Introduction
  2. Raw materials
  3. Porcelain powder
  4. Firing
  5. Properties
  6. Ways of making a restoration

Introduction

Dental ceramics are the most esthetic and biologically inert restorative materials. Porcelain, a fine, non-porous ceramic, first appeared in China, and in Europe J. Böttger made it in Meissen in 1709.

Raw materials

The minerals are heated to 1300 to 1500 °C and then cooled very quickly in cold water, which shatters them. This product, the frit, is milled and sifted into powder.

Porcelain powder

  • Modifiers (fluxes): oxides that lower the sintering temperature and adjust thermal expansion.
  • Colorants: heat-resistant metal oxides.
  • Luminophores: rare metal oxides that give fluorescence.
  • Plasticizers: dextrin, sugar or starch, which hold wet particles together. They burn off in the furnace.
  • Organic dyes: dentin powder is coded pink and enamel powder blue, so the technician can see the layers. These also burn off.

Firing

The powder is mixed with distilled water into a creamy mass and built up in layers. The piece is vibrated to bring water to the surface, and this is blotted away. It is then fired in a vacuum furnace.

  1. Drying: at the furnace door, up to about 120 °C.
  2. Burning off: at about 600 °C for 5 to 10 minutes. The mass is about 50% porous.
  3. Sintering: at about 980 °C for 6 to 7 minutes. The particles bond without melting, and the vacuum draws out gases.
  4. Slow cooling, correction and refiring.
  5. Glazing: heating just the surface until it flows, or adding a thin transparent glaze, without vacuum.

Porcelain shrinks by about 18% in firing, so the crown is modeled slightly larger.

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