Choosing the correct cement for all-ceramic crowns can be tricky because of the wide variety of available materials. All-ceramic crowns are typically cemented adhesively using glass ionomer cement. They can also be bonded with composite resin cement. Selecting the correct cement when fitting an all-ceramic crown can contribute to its longevity. Additionally, the cement available for different types of all-ceramic crowns require specific surface treatments to be used, which optimizes bonding.
Today’s modern cement is designed to provide excellent marginal integrity, which helps to compensate for any tiny discrepancies between the tooth preparation and the restorative material. Even with the use of CAD/CAM technology, that provides an extremely precise fit, an all-ceramic may not be absolutely perfect. Contemporary cement is more retentive, but successful cementation is also dependent on the correct tooth preparation. This includes the proper margin design and specific reductions to ensure sufficient clearance. A good design will help provide the restoration with the correct contours, shape, and fit that are compatible with good gingival health as well as great aesthetics.
There are two different types of all-ceramic crowns: silicate ceramics and oxide ceramics. Silicate ceramics include lithium disilicate ceramics like IPS e.max leucite-reinforced porcelain, which includes IPS Empress. Oxide ceramics include zirconia, and although these restorations have a high-strength, they are generally less aesthetic compared to silicate ceramics.
When cemented with composite resin cement, silicate ceramics can be etched with hydrofluoric acid to enable better bonding. When silicate ceramics are acid etched and bonded, it helps to improve the physical properties of the porcelain. This is because silicate ceramics tend to be more brittle in nature, and using an adhesive composite resin cement helps to strengthen the etched porcelain because it locks into the microscopically-roughened surface, preventing microcracks from permeating through the porcelain. All-ceramic crowns that are made from leucite-reinforced ceramic and can be cemented or dual-cured, self-cured, or light-cured. Crowns made from lithium disilicate are slightly more opaque compared to leucite-reinforced ceramic crowns. It is best to cement these crowns using self-adhesive, dual-cured, or self-cured resin cement. Due to the thickness and opacity of lithium disilicate crowns, light-cured resin cement is generally not advised.
The crowns are made using metal oxides and are highly resistant to fracturing. Oxide ceramics are also resistant to being etched, but sandblasting the surface can help to make it more adhesive. Usually, oxide ceramics such as zirconia crowns can be cemented in place with the same types of cement used for PFM restorations. These include dual-cured composite resins, glass ionomer cement, and self-cured composite resin, as well as a self-adhesive composite resin cement. One of the easiest and most forgiving cements is resin-modified glass ionomer or alternatively-adhesive composite resin cement. With these materials, there isn’t any need to use a separate bonding agent, although some manufacturers do provide a surface primer to be used before seating a crown with composite resin cement.
Before cementing any all-ceramic crown, make sure the tooth is properly cleaned. Using unit-dose mixed capsules and self-mixing cement provides a more uniform mix. When using resin-based cement and resin-modified glass ionomer, remember these are thixotropic and will flow under pressure. It is important to read all the instructions for using the cement and for storing them correctly. If the cement has to be refrigerated, ensure it is removed from the refrigerator at least an hour before use, allowing it to slowly reach room temperature.
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References:
https://www.dentalaegis.com/id/2013/12/cements-for-all-ceramic-materials