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Are You Using the Best Cement for the Job? Gary Alex, DMD

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by Gary Alex, DMD

There is a trend in dentistry toward simplification. This is readily apparent with the emergence of so-called universal bonding agents and cements that manufacturers claim can be used for virtually all adhesive and cementation scenarios. While universal adhesives and cements have the potential to reduce product inventory and simplify placement protocol, a universal material may not, in fact, be the best choice in all clinical situations.

When it comes to cementation there are many factors to consider before deciding on the use of a specific class of cement and placement protocol, including the nature of the tooth and restoration substrate being cemented or bonded, inherent retentiveness of the preparation, access and control of the working area, ease of use and cleanup, and aesthetics. While other cementation options exist, and excluding porcelain veneers, the majority of dentists today use one of three distinct classes of materials for the fi nal cementation of their restorations.

  • Resin modifi ed glass ionomers (e.g. FujiCem-2 GC, 3M ESPE RelyX Luting Plus)
  • Dual-cure self-adhesive resin cements that are placed without the use of a separate dentin bonding agent (e.g. 3M ESPE RelyX Unicem 2, Kerr Maxcem, BISCO Bis-Cem and GCG-Cem)
  • Dual-cure resin cements that are used in conjunction with a separately placed dentin bonding agent (DB A) (e.g. 3M ESPE RelyX Ultimate Adhesive Resin Cement, BISCO Dual-Link and Ivoclar Multilink)

Resin Modified Glass Ionomers (RMGIs)

I consider RMGIs to still be one of the best, and one of the most underrated, cementation options. In fact, unless retention is an issue, RelyX Luting Plus (3M ESPE) is my default cement for all full coverage zirconia, PFM and cast gold restorations. In all cases, the intaglio surface of the restorations should be sandblasted prior to cement placement. In addition, I like to use a zirconia primer such as Z-Prime (BISCO) on the intaglio surface when cementing zirconia restorations.

RMGIs have many positive attributes, including good physical properties, low solubility, chemical bond to tooth structure, low film thickness, significant fluoride release, anti-microbial activity, proven long-term track record and low incidence of post-operative sensitivity. One of the biggest clinical advantages of RMGIs is that they are very easy to mix, place and clean. In fact, cement cleanup is generally much easier with RMGIs when compared to resin cements. This fact alone makes RMGI an attractive cementation option. RelyX Luting Plus also has a tack-cure option that allows almost immediate cement clean-up in the margin areas.

On the downside, RMGI cements are not as retentive as the two classes of resin cements that have a distinct advantage over RMGI cements when it comes to bonding restorations on or in minimally retentive preparations. This is because resin cements have the potential to bond more durably to both the tooth structure and the restorative material. Resin cements are also generally the best choice when placing porcelain restorations that can be etched with hydrofluoric acid as resin cements bond extremely well to etched porcelain and optimize overall assembly strength. In addition, resin cements are often a better choice for restorations placed in the aesthetic zone, because RMGI cements tend to be opaque and can show through many restorations (such as translucent lithium disilicate) which results in unacceptable aesthetics.

Self-adhesive Resin Cements

Dual-cure self-adhesive resin cements were developed as an alternative to traditional resin cements. When initially developed, the use of resin cements first required conditioning of the tooth tissues (usually with phosphoric acid) followed by the application of a DBA. Self-adhesive resin cements eliminated this step by essentially having the cements themselves condition and prime the tooth substrate. You could say the etching and priming steps are essentially built into the chemistry of self-adhesive resin cements. Elimination of the etching and priming steps saves considerable time, and this class of cements is currently very popular among clinicians. In fact, one product in this class, 3M ESPE RelyX Unicem 2, has been the best selling cement in the USA for several years. Cements in this category are generally stronger, have better physical and esthetic properties, are more versatile and more retentive than RMGI's.

On the downside, these cements have much less fluoride release and cleanup can be more difficult compared to RMGIs. I strongly advise those using self-adhesive resin cements to allow these materials to self-cure on their own and then follow-up with light-curing to ensure maximum polymerization. There may be several good reasons for allowing the cement to self-cure before light curing. In principle, the chemical interactions that need to occur for a self-adhesive resin cement to actually interact with tooth tissues take some degree of time and should take place while the material is in a fluid state. In this way, molecular movement and interaction with tooth tissues is optimized. If the cement is tackcured or light polymerized immediately after seating the restoration, the cured cement may limit the degree of molecular interaction because it's harder for things like molecules to move around in the set cement. In addition, there is a window of opportunity during the self-cure mode when the resin cement gels up and is relatively easy to remove. Conceptually, there may also be advantages in terms of stress development by allowing the resin cement to cure more slowly during the self-cure mode, providing more time for both the tooth and restoration to adapt as stress develops.

Resin Cements used with a DBA

ith the emergence of self-adhesive resin cements, dentists might ask why even use a resin cement with a DB A anymore, as it takes more time and additional steps. The primary answer is bond strength. If the goal is to optimize bond-strength, then a DBA followed by a traditional resin cement is still the way to go. I routinely use products such as Scotchbond Universal Adhesive (3M ESPE) along with RelyX Ultimate resin cement or All-Bond Universal and Dual Link (BISCO) in situations where I want maximum retention (such as minimally retentive preparations and wings for resin bonded bridges). A significant problem with this class of resin cement is that cleanup of the fully set cement can be extremely challenging. As with self-adhesive resin cements, I recommend allowing the cement to self-cure prior to light curing and cleaning before fully set.

Conclusion

I think the idea of a universal cement is laudable, but not necessarily practical. At this point, I think clinicians have to tailor their choice of what cement to use based on the specific clinical situation, the material they are placing, the best current available research, and their own clinical experiences. This requires that clinicians be knowledgeable about a range of cement categories in order to select the most appropriate cement for the job.



Dr. Alex graduated from Tufts University Dental School in 1981 and continues to enhance his dental education by completing numerous hours of continuing education with an emphasis on occlusion, adhesion, comprehensive dentistry, materials and esthetics. An international researcher and lecturer, Dr. Alex is an accredited member of the American Academy of Cosmetic Dentistry, International Association of Dental Research, American Equilibration Society and is co-director of the Long Island Center for Dental Esthetic and Occlusion. Dr. Alex maintains a practice in Huntington, NY that is geared toward comprehensive prosthetic and cosmetic dentistry.
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