INTRODUCTION
With the many choices of cements and restorative materials available to dentists today, there is often confusion as to which type of cement is the best for each type of restoration, whether it be crown, onlay, or multiple-unit fixed prosthesis. The 3 most common material categories of crowns in use today are all-ceramic (80%), PFM (17%), and full cast (3%).1-2 This is a significant change from a previous report published 7 years ago by the National Association of Dental Laboratories and Glidewell Laboratories.2 In 2007, nearly 66% of all crowns produced were PFM, while all-ceramic crowns were at only 24% and full cast at 8%.2 The rapid change by dentists from PFM to all-ceramic crowns has been viewed as “one of the fastest and most significant paradigm [shifts] in the history of dentistry.”2 Porcelain-fused-to-gold (PFG) crowns, however, are still considered the “gold standard” by which other materials are measured for maximum strength and long-term durability. They have a proven history of more than 50 years of research and clinical observation.2 The newer generation of ceramic crowns, (ie, milled full-zirconia, zirconia core with ceramic laminate fired or pressed on, or pressed and milled lithium disilicate), although increasingly popular by a wide margin, are still relatively new with only a few years of long-term study.2 The direction is clear, however, that all-ceramic crowns are the way of the future.2-4
The 2 most popular types of permanent cements for crowns and fixed prostheses are resin-modified glass ionomer (RMGI) luting cements and adhesive resin cements which are bonded to the tooth structure. Resin cements are available in dual-cured, self-cured, and light-cured variations in multiple shades (depending upon need), while RMGI cements are usually available in an opaque light shade. To “lute” or to “bond” a restoration is the question, and both types of cements have their advantages, drawbacks, and indications.1,5
Self-cured RMGI cements are suitable for cementation of any crown that has a core, whether it is a metal (ie, gold or semiprecious PFMs) or a high-strength (metal oxide) or other polycrystalline ceramic (ie, aluminum oxide, zirconium oxide, or lithium disilicate [Editor’s note: not for leucite-reinforced or feldspathic porcelains]) where modification of the tooth shade is not an issue. The guideline is that the tooth preparation should have parallel axial walls (ideally 5° to 7° taper) and adequate axial wall length (minimum of 3.0 to 4.0 mm) to provide proper retention and resistance form. If the crown is less retentive, then an adhesive resin cement is indicated.1,2 The advantage of RMGI cements is in ease of handling and cleanup, since resin cements often adhere to almost everything, and removal of excess resin cement may take a little longer if allowed to set completely. Another advantage of RMGI cements is that the removal of the crown may be a bit easier if replacement is necessary. Metal crowns cemented with RMGI cements are easily removed by splitting the crown with a carbide bur or diamond instrument, and using a screwdriver type of crown remover (such as the CRCH1 straight Christensen Crown Remover [Hu-Friedy]) to twist the segments apart.
Resin cement-bonded lithium disilicate, or especially zirconia-based crowns, are far more difficult to remove, and diamond burs (such as Two Striper ZTech [Premier Dental Products], Great White Z Diamonds [SS White Burs], 4ZR Diamond Crown Cutter [Komet USA], DuraCut [Brasseler USA], and Predator Diamond Burs [CLINICIAN’S CHOICE]) have been designed to assist with this task when needed. Care must be taken to not remove more tooth structure than necessary since it is often difficult to differentiate among tooth structure, cement, and porcelain. Generally, if resistance and retention form are adequate in the prepared tooth, an RMGI cement is suitable for porcelain or PFG crowns. Zirconia crown cores are usually opaque; however, when a lithium disilicate or other translucent porcelain crown requires color modification, then an adhesive resin cement may be indicated, since they are available in multiple shades. Porcelain inlays and onlays are optimally cemented using adhesive resin cements, and both types of cements show very low postoperative sensitivity.1,2,6,7
CASE 1
Cementation of a PFG Crown With a Dual-Cured RMGI Cement
In this case, the use of a proven and time-tested self-cured RMGI cement (RelyX Luting Plus [3M ESPE]) will be demonstrated. This cement has a unique feature that allows the clinician to tack-cure margins with a conventional curing light for 5 seconds to clean up the excess cement easily. Unlike all-resin cements, you cannot overdo the 5-second tack-cure since it is very forgiving clinically. This cement is radiopaque, fluoride releasing, and virtually no postoperative sensitivity has been observed/reported with its use. The cement is indicated for the permanent cementation of PFM crowns and bridges; metal crowns, inlays/onlays; lithium disilicate, aluminum or zirconium oxide crowns; cast posts; stainless steel crowns; and orthodontic appliances.
Figures 1 to 4 show an endodontically treated tooth No. 19 presenting with an internal fracture and requiring a full-coverage restoration. In this case, a PFG crown was chosen because of the solid reputation for long-term durability of this material, and also due to the somewhat guarded prognosis because of the partial internal fracture.4,5 After the post and core was placed, the preparation was completed. A vinyl polysiloxane impression (Aquasil Ultra [DENTSPLY Caulk]) was taken. A PFG crown was then fabricated by our dental laboratory team (Figure 5) and returned to the office for delivery. (Note the sandblasted internal aspect of the crown to improve retention prior to cementing [Figure 6].)
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At the seating appointment, the temporary crown was removed, the preparation was cleaned with glutaraldehyde for antimicrobial control, and the crown adjusted. The preparation may be isolated and left slightly moist with glutaraldehyde.5 A small amount of RelyX Luting Plus cement was dispersed onto a mixing pad to ensure proper flow and mixing in the automix tip. The inner aspect of the crown (intaglio surfaces) was coated with the RMGI cement up to the margins (Figure 7 shows buccal margin not coated yet), but was not overfilled. The mousse-like consistency of this cement allows the clinician to coat the internal restoration surfaces easily. Once the crown was seated, the margins were then tack-cured with a curing light for 5 seconds, allowing for an easy and quick cleanup (Figure 8). The cement does not reach an initial set underneath the crown for 2 minutes, so the crown was held in place with an instrument during the cleanup process (Figure 9).
The completed PFG crown on tooth No. 19 should provide years of service for the patient (Figures 10 and 11).
CASE 2
Luting a Ceramic/Composite Inlay Using a Dual-Cured Adhesive Resin Cement
The cement used in this case for the placement of a ceramic/composite inlay was an all-purpose dual-cured resin cement (RelyX Ultimate Adhesive Resin Cement [3M ESPE]). It was used in conjunction with a universal adhesive (Scotchbond Universal [3M ESPE]). The cement comes in an automix syringe with tips of various sizes for ease of application. The unique feature of this cement is that it is a dual-cured resin cement paired with a self-etching primer.6 Since the cement contains an integral dual-cured activator, the universal adhesive can be used alone without any additional dual-cure activator and needs no light curing prior to seating the restoration. This (no need for light curing) allows for a better fit and a choice of either self-etch, selective-etch, or total-etch technique.6 RelyX Ultimate cement can be used for the cementation of almost all indirect restorations and is available in 4 shades. When combined with Scotchbond Universal Adhesive, RelyX Ultimate is suggested for the final cementation of all ceramic, nanoengineered resin ceramics, composite or metal restorations, including inlays/onlays, crowns, bridges, Maryland bridges, and aesthetic posts.7
Tooth No. 30 had a failing amalgam restoration with caries present (Figure 12). A conservative CAD/CAM (CEREC [Sirona Dental Systems]) was indicated. A simple preparation with no undercuts was made, followed by placement of an indirect pulp cap with calcium hydroxide and a dual-cured GI cement liner (Fuji LINING LC Paste Pak [GC America]) (Figure 13).
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A Lava Ultimate (3M ESPE) block restoration was designed and milled (Figure 14), then tried in place. After try-in, the restoration was finished and polished extraorally with polishing wheels (Sof-Lex Spiral Finishing and Polishing Wheels [3M ESPE]) designed specifically for direct and indirect composite and these new nano resin-ceramic (Lava Ultimate [3M ESPE]) restorations, using a straight handpiece (Figure 15). No carbide or diamond instruments were necessary to achieve a high luster. The beige wheel was used first since the abrasive is coarser, followed by the white wheel for final polishing as shown. The restoration’s surface to be cemented was then sandblasted with 50-µm aluminum oxide. A disposable applicator was then used to apply a universal adhesive (Scotchbond Universal) to the surface to be bonded, rubbed in for 20 seconds, and then blown with a gentle stream of oil-free air for 5 seconds. (Note: The adhesive was not light-cured at this point.)
Although a clinically adequate bond can be achieved with only self-etch Scotchbond Universal combined with RelyX Ultimate Adhesive Resin Cement, enhanced bond strength was achieved by selectively etching the enamel with Scotchbond Universal Etchant (3M ESPE) for 15 seconds, followed by washing for 15 seconds, and then drying. The adhesive was then applied to the entire tooth structure and rubbed in for 20 seconds. Then, a gentle stream of oil-free air was blown over the surface until the liquid no longer moved and the solvent was evaporated entirely. Next, a new automix tip was placed on the RelyX Ultimate syringe and a small amount of cement was squeezed out onto the pad until an evenly mixed homogenous colored paste flowed out of the tip. The cavity walls and floor of the inlay preparation were coated with the cement, and the restoration was seated to place. (Crowns would require coating the inside of the restoration with cement instead.) Excess was removed using a Microbrush (Microbrush International) before the cement was set.
The occlusion was then minimally adjusted and finished with carbide finishing burs (Brasseler H379-023/OS-1 football-shaped carbide finishing bur and 274-016 small-pointed carbide bur [Brasseler USA]). A final high luster polish was achieved intraorally by using just the same spiral finishing and polishing wheels used earlier. No abrasive rubber finishing or polishing points or cups were necessary (Figure 16).
Figure 16 demonstrates the high natural luster that can be achieved with the Lava Ultimate restorative material. Studies have shown that nano resin-ceramic materials are kind to opposing teeth, have shock absorbency, are repairable, and show wear and fracture resistance similar to porcelain inlays and onlays.8
IN SUMMARY
The conventional RMGI luting cement described and demonstrated herein (Case 1) is ideal for the permanent cementation of all retentive porcelain PFM crowns and bridges; metal crowns, inlays/onlays; lithium disilicate or zirconia core crowns; cast posts; stainless steel crowns; and orthodontic appliances. It is easy to handle and clean up.
The adhesive resin cement described and demonstrated herein (Case 2) (Figure 17) is intended for combination with Scotchbond Universal Adhesive, and suggested for the final cementation of all less retentive ceramic, nanoengineered resin ceramics, composite or metal restorations including inlays/onlays, crowns, bridges, Maryland bridges, and aesthetic posts. The clinician has a choice with this material to use either a dual-cured bonding approach or, if indicated, combined with Scotchbond Universal Adhesive as either a self-etch, selective-etch, or total-etch cementing technique.
Cleanup may be just a little more difficult with a resin bonding cement than an RMGI cement, but both are excellent choices depending on the clinical indication at hand. With careful attention to the clinical situation, dentists can select the cement that will perform reliably and best serve the patient for long-lasting results.F
References
- Christensen GJ. Use of luting or bonding with lithium disilicate and zirconia crowns. J Am Dent Assoc. 2014;145:383-386.
- Christensen GJ. Is the rush to all-ceramic crowns justified? J Am Dent Assoc. 2014;145:192-194.
- Donovan T. Restoration of the worn dentition. Presented at: Chicago Dental Society Midwinter Meeting; February 23, 2008; Chicago, IL.
- Goodacre CJ, Bernal G, Rungcharassaeng K, et al. Clinical complications in fixed prosthodontics. J Prosthet Dent. 2003;90:31-41.
- Roberson TM, Heymann H, Swift EJ Jr. Sturdevant’s Art and Science of Operative Dentistry. 5th ed. St. Louis, MO: Mosby; 2006:225-227.
- Miller MB. Resin/glass ionomers – luting cements. Reality—Volume 22. Houston, TX: Reality Publishing; 2012:1154-1160, 1278-1283.
- Farah JW. 3M ESPE RelyX Ultimate Adhesive Resin Cement. The Dental Advisor. 2012;29 (5).
- Fasbinder DJ, Dennison JB, Heys DR, et al. The clinical performance of CAD/CAM-generated composite inlays. J Am Dent Assoc. 2005;136:1714-1723.
Dr. Weinstein is a graduate of the University of North Carolina at Chapel Hill School of Dentistry and has had faculty affiliation with the Cincinnati Children’s Hospital Medical Center for more than 25 years. He is a member of the ADA, the Academy of Operative Dentistry, and International Association for Dental Research, and he is a Fellow in the International College of Dentists. He maintains a private practice in Cincinnati, which emphasizes conservative aesthetic and preventive restorative dentistry. He serves as a consultant with various manufacturers of dental materials and has contributed articles to several dental journals, including the Journal of the American Dental Association, Dental Clinics of North America, Dental Economics, and Dental Products Report. He has lectured internationally on enamel bonding, conservative restorative techniques, and integrative dental medicine. For the past 20 years, he has presented courses on mind/body health and stress-related illness throughout North America. He can be reached at (513) 793-1977 or at arwdds@aol.com.
Disclosure: Dr. Weinstein discloses that he has receieved funding from 3M ESPE for this trial and article.
