- The characteristic translucency of dental porcelain is primarily due to the presence of feldspar.
- Feldspar acts as a fluxing agent during the firing process, which lowers the melting temperature of the mixture and leads to the formation of a glassy matrix.
- This matrix is critical because it closely mimics the optical properties of natural tooth enamel, allowing light to pass through the material in a way that creates a lifelike appearance.

Here's a breakdown of the roles of the other ingredients:
- Glass frit is mainly added to improve the fusion and handling properties of the porcelain but does not significantly impact translucency.
- Kaolin is a type of clay used to provide plasticity and shape during the forming stage; it does not influence optical properties.
- Quartz provides mechanical strength and stability but tends to increase opacity rather than translucency.

Therefore, feldspar is the key component responsible for the translucency in dental porcelain, making it indispensable for creating restorations that resemble natural teeth.

Reference: Phillips' Science of Dental Materials, 12th Edition, Chapter 8, Pages 193-195