Introduction
An all-ceramic crown has no metal at all. Ceramics can copy the colour, surface texture and translucency of natural teeth so closely that a well-made crown is almost invisible. The trade-off is that ceramics are brittle, so material choice and preparation decide whether the crown survives.
Two ways to build a crown
- Layered: the technician builds up several porcelains (dentin, enamel, incisal) on a ceramic core: the most lifelike colour.
- Monolithic: milled from one block by CAD/CAM (or pressed): stronger and quicker, but one shade, less translucent; characterized with stains.
Preparation
- Shoulder (or deep chamfer) about 1 mm wide all around, with a rounded internal angle.
- Incisal or occlusal reduction 1.5–2 mm.
- Margins at or above the gingiva, which suits adhesive cementation.
- No undercuts, no sharp edges or right angles: ceramics crack from stress at sharp corners.
- Uniform reduction so the ceramic has an even thickness.
Cementation
Glass-ceramics are bonded adhesively: the inside is etched and silanized, then luted with a composite cement, which raises the crown's strength and lets its translucency show. Zirconia can be cemented conventionally (glass-ionomer) or adhesively after sandblasting.