Ray E. Stewart, DMD, MS, discusses the ideal characteristics dental cements should have when being used for pediatric crowns.
A few years ago, it seemed that "the verdict was in" regarding what cement to use for a full-coverage crown restoration on a primary tooth. Before 2010, the only full-coverage, preformed crowns available were either stainless steel or pre-veneered stainless steel crowns. Glass-ionomer cements were the most common choice for cementing them.
With good adhesion to both dentin and stainless steel, a relatively short set-time, and good moisture tolerance, glass-ionomer cements were-and still remain-a good choice for these restorations.1,2
But over the last five years, technology has advanced dramatically, and preformed zirconia crowns are now available from several manufacturers. Zirconia crowns are becoming increasingly popular and are being covered by Medicaid and private insurers in more states each year. This raises the question, "Are glass-ionomer cements still the best, most cost-effective option for pediatric crowns?"
Numerous studies on the cementation of zirconia crowns to permanent teeth help provide part of the answer, while also reinforcing the fact that zirconia is truly a unique material. It is difficult to form any chemical bond to zirconia, and few cements have the ability to form a strong bond. Both in-vitro and clinical trials have shown that, while glass-ionomer cements often do not form an effective bond to zirconia, some resin cements and some resin-modified glass-ionomer cementation systems are very effective.
So we've now found the answer, right? Just use the resin or resin-modified glass-ionomer cement of your choice that is indicated for zirconia . . . well, not quite! Many of the resin and resin-modified glass-ionomer cementation systems developed for general dentistry incorporate cleaners to remove saliva contamination from the intaglio surface of the crown and also require a primer to create the bond between the clean zirconia surface and the cement.3 These same cementation systems often require an etchant, primer, or both to create a bond between the dentin and the cement. While these cementation systems ultimately create a strong bond and are good solutions for the general dentist using a custom-fit zirconia crown to restore a single permanent tooth, they are not practical or cost-effective for the pediatric dentist. Using these complex bonding systems to restore multiple teeth consumes too much valuable chair time and negatively impacts the profitability of the practice. Some of the newer cementation systems are self-etching and/or self-priming, but this comes with a higher price tag. Additionally, many of these systems are not moisture-tolerant, requiring total isolation and a pristinely dry, hemorrhage-free field-which is unlikely in a pediatric environment.
Using a glass-ionomer cement on a zirconia crown can work in some cases, but if the remaining tooth does not have sufficient "retentive form" available, a sufficiently strong bond may not be achieved. Also, if the tooth/crown margin at the gingival edge is too open, the restoration runs the risk of premature failure and/or secondary decay due to wash-out; this is a problem that seldom occurred with the closed margin provided by a snap-fit stainless steel crown. No pediatric dentist wants a return visit from a parent bringing in a child whose crown has come off; not only would this lead to client dissatisfaction, but many times it would also cause the second appointment to be free or deeply discounted, which would erode practice profitability.
When considering the many cement choices available, it's safe to say that there are a number of properties that characterize the "ideal" cement for pediatric full-coverage crowns:4
• Proven, evidence-based high bond strength to both zirconia and stainless steel
• Handling properties optimized for pediatric dentistry:
- A self-set time of 2-3 minutes, providing enough working time to place and position the crown but not so much time as to delay the procedure and increase chair time
- The ability to accelerate curing with a curing light to aid in cleanup of excess cement at the crown margin and to light-cure through a zirconia crown to further expedite the procedure
- A viscosity high enough to bulk fill crowns but with a low enough film thickness to allow the correct fit in all situations
- A delivery system that is easy to use and that minimizes waste
- Esthetics (color) compatible with translucent zirconia crowns
• Stability over time and resistance to wash-out (low water solubility) in the oral environment
• High biocompatibility and low cytotoxicity (which is increasingly important to parents)5
• Bioactivity at a minimum high fluoride release (as some of the newest "bioactive" cements provide much more)
• Cost-effectiveness compared to traditional glass-ionomer cements
There are few cements that fit all or even most of these criteria. I've tried two of these: Ceramir (Doxa Dental) and BioCem (NuSmile). A big benefit to both cements is their ability to form hydroxyapatite to integrate with and replenish tooth structure; however, BioCem also releases three beneficial ions: phosphate, calcium, and fluoride. It also does not require trituration.
So if you have already started using zirconia crowns in your pediatric practice, make sure to review your cement formulary to see if the cement you are using is indicated for both stainless steel and zirconia restorations. If you are new to zirconia, make sure that a review of your cement formulary is part of your "due diligence" when bringing zirconia into your restoration arsenal. Either way, the good news is that there are now cements available that fit the criteria above, so make sure you do your homework and choose one that is up to the task.
References
1. Croll TP, Nicholson JW. Glass ionomer cements in pediatric dentistry: review of the literature. Pediatr Dent. 2002;24(5):423-429.
2. Nicholson JW. Glass ionomer dental cements: update. Mater Tech Adv Perf Mater. 2010;25(1):8-13.
3. Yang B, Lange-Jansen HC, Scharnberg M, Wolfart S, Ludwig K, Adelung R, et al. Influence of saliva contamination on zirconia ceramic bonding. Dent Mater. 2008;24(4):508-513.
4. Hill EE. Dental cements for definitive luting: a review and practical clinical considerations. Dent Clin North Am. 2007;51(3):643-658.
5. Nicholson JW, Czarnecka B. The biocompatibility of resin-modified glass ionomer cements for dentistry. Dent Mater. 2008;24(12):1702-1708.
Ray E. Stewart, DMD, MS, is a director of the Institute for the Clinical Practice of Pediatric Dentistry and the author of numerous books and articles on pediatric dentistry. He is a former director of the Craniofacial Anomalies Clinic at the University of California, Los Angeles (UCLA), director of pediatric dentistry at UCLA-Harbor General Hospital, and executive director of the California Society of Pediatric Dentists.
