Describe the process of sintering during the laboratory fabrication of a ceramic restoration.

Describe the process of sintering during the laboratory fabrication of a ceramic restoration.

1. "Sintering is the process of compacting and forming a solid mass of material by heat or pressure without melting it to the point of liquefaction. The heating cycle causes the particles in the mix to bind together by a process called sintering. This is when particles in close proximity to each other are heated to a point where their edges and corners start to become rounded, and they stick together. "

2. 1. Initially, the unfired or "green" porcelain is placed onto a saggar, and the saggar is placed within the furnace muffle.

3. 2. The liquid binder is driven off and the porcelain becomes brittle and chalky.

4. 3. At this stage, the green porcelain is introduced into the hot zone of the furnace and the temperature is raised to the firing temperature of the porcelain

   • It is best at this stage if the powder is regarded as a glass powder.

5. 4. During firing the glass particles soften at their contact points (grain boundaries) and fuse together.

   • This partial fusion is often referred to as sintering.

6. 5. As the furnace temperature is raised to the firing temperature of the porcelain the original air spaces left after condensation of powder escape via the grain the boundaries of the glass powder by the action of surface tension.

7. 6. As the air is removed from between the powder grains before sealing of the surface occurs, there is nothing to prevent the porcelain from shrinking to a pore-free mass.