Dr Elsayed, all-ceramic restorations require adhesive luting. Is this true for other restorative materials, such as zirconia, lithium disilicate and hybrid ceramics?
Yes and no. Several factors must be taken into account. Firstly, material properties must be considered, especially flexural strength. Fortunately, clear guidelines based on scientific studies are available. One such guideline states that all materials with a flexural strength of less than 350 MPa should be placed with an adhesive luting agent. Correct adhesive luting stabilises the restoration and tooth structure. Restorative materials of higher strength, such as reinforced glass-ceramics, lithium disilicate ceramics and zirconia, can be cemented with conventional methods. However, some studies indicate that an adhesive luting agent can improve overall stability, whereas others show no significant difference.

Another factor guiding the decision for or against adhesive luting is the preparation design. For crowns and bridges, the decisive factor is whether the operator has been able to adhere to the preparation guidelines (minimum abutment height of 4 mm and maximum convergence of 15°)^1–5 in order to create the required retention and resistance form for conventional cementation. Minimally invasive restorations, such as resin-bonded fixed dental protheses (FDPs), veneers and inlay FDPs, are based on a non-retentive preparation design. In such cases, only adhesive luting can ensure adequate retention.

Aesthetics is another important factor. Besides the restorative material, the luting material also has a major impact on the optical outcome. For highly translucent ceramics in particular, adhesive luting is recommended. Whereas conventional cements are usually only available as opaque materials, resin composites come in different colours with higher colour stability. Examples are PANAVIA V5 and PANAVIA SA Universal.

How should the surface be pretreated or conditioned for adhesive luting?
Pretreatment of the surface depends on the structure or microstructure of the ceramic. Silicate ceramics, like glass-ceramics, have a glass phase and can be etched. Etching increases the surface area, thus preparing it for adhesive luting. In contrast, oxide ceramics like zirconia as well as composites have a negligible amount of glass phase or none at all. They cannot be etched. Their surface is conditioned by air abrasion with aluminium oxide. This is the only method that has been proved scientifically to achieve a dependable bond with these materials and is the one currently used.

How important is the correct cleaning of the tooth and restoration surface for the quality of the bond?
The restoration surface must be decontaminated immediately prior to luting. Contaminants must be removed thoroughly. Rinsing with water or alcohol has been shown to be insufficient. Therefore, cleaning solutions such as KATANA Cleaner have been developed. Any contamination is detrimental for the adhesive bond. At try-in of the restoration, for example, its surface becomes contaminated. Saliva, blood and other substances accumulate and the proteins contained in these substances act to isolate all subsequently applied components such as the primer. Any contamination must therefore be thoroughly removed prior to the bonding procedure. This is also the case for direct adhesive restorations. KATANA Cleaner offers a simple and quick way to accomplish this task.

What makes KATANA Cleaner so interesting for the user?
The special features of KATANA Cleaner are its integrated MDP salt and its mild pH value. Let us consider the function of the MDP salt, specifically. Rubbed in for 10 seconds, the cleaner causes the contaminant particles—such as remnants from the work process and proteins from saliva and blood—to adhere to the MDP salt as to a magnet. The contamination is flushed off the surface by rinsing with water. This ability is attributable to the MDP salt and makes KATANA Cleaner interesting and easy to use. In addition, the pH value allows the use of the cleaning solution both intra-orally and extra-orally, which is another special feature. We generally recommend the use of KATANA Cleaner for both direct and indirect restorations. Thanks to the universal applicability of the cleaning solution, only one material is needed, and the time required is minimal. Cleaning with KATANA Cleaner is recommended even for bonding abutments on a titanium base because it provides an ideal basis before the application of the primer. In this case, contamination from sources such as finger grease and residues of the air abrasive could act as an insulator and impair the quality of the bond.

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