What technique can be used to create a matte finish and increase retention on the intaglio surface of a crown before cementation?

Using aluminum oxide air abrasion is an effective technique for creating a matte finish on the intaglio surface of a crown, which in turn increases the retention when cementing the crown in place. This method involves delivering tiny particles of aluminum oxide at high speed onto the surface, which roughens it, enhancing surface area and mechanical retention of the cement.

The matte finish produced by air abrasion increases the effectiveness of the bond by providing more micro-retentive areas for the cement to adhere to, thus reducing the risk of crown dislodgement. It's particularly useful for crowns made of ceramics or metal that may require a mechanical interlock with the cement rather than a purely chemical bond.

In contrast, other techniques like using a fine diamond or polishing disc would tend to smooth the surface rather than create the necessary texture for optimal retention. Hydrofluoric (HF) acid is often used for etching glass-ceramics to create surface irregularities, but it is less common for creating a matte finish specifically intended for increasing retention in this scenario.