- In dental ceramics, controlling the optical properties such as translucency and opacity is crucial for achieving both aesthetic and functional outcomes.
- Among the additives used, alumina (Al₂O₃) is commonly incorporated to enhance the opacity of dental ceramics.

- Alumina is a white, opaque material that, when added to dental ceramics, increases their scattering of light, thereby reducing translucency and making the ceramic appear more opaque.
- This property is essential in situations where masking of underlying structures such as metal cores or discolored tooth structure is needed.
- Zirconia, another commonly used additive, also provides opacity but is primarily valued for its high strength and toughness rather than solely increasing opacity.
- Silica is the main glass-forming component in ceramics and generally contributes to translucency rather than opacity.
- Titanium dioxide (TiO₂) can be used as a pigment and opacity agent in some ceramics but is less commonly used compared to alumina in dental ceramics.

Therefore, alumina is the preferred additive to enhance opacity in dental ceramics because of its effective light-scattering properties.

Reference: Craig's Restorative Dental Materials, 13th Edition, Chapter 7: Ceramic Materials, Page 205