by Jeffrey B. Dalin, DDS, FACD, FAGD, FICD
Dr. Dalin: Dr. Fier, thank you for talking with me this month about dental cements. I think this is one area of dentistry that needs to deliver the best in its properties. First, let’s discuss the different categories of permanent cements. Would you discuss a few positives and negatives about the various types: zinc phosphate, polycarboxylate, glass ionomer, resin, and resin ionomer?
Dr. Fier: Certainly Jeff. Using your order, let’s start with zinc phosphate, commonly referred to as ZOP. Some brand names for this group are Fleck’s and Tenacin. A big positive is that it has the longest track record of any of the cements and, generally, the lowest cost. But ZOP has many disadvantages. It is not truly adhesive to tooth structure or the many restorative materials we use. ZOP “cements” two surfaces together by mechanical interlocking, filling the space between the irregularities of the tooth preparation and the cemented restoration. Dentists who have used ZOP know that using it is technique-sensitive. I remember having to cool a glass slab, mix small amounts of powder into the liquid, and spread it over a wide area so that the powder was incorporated homogenously. Compared to some of today’s cements, ZOP is challenging.
Polycarboxylates, such as Durelon, appeared in the late 1960s. This group is a step up since these cements do chemically adhere to tooth structure. The setting reaction produces little heat, which is very friendly to the pulp, and there is generally no postoperative sensitivity when a polycarboxylate is used. On the other side, I think the biggest negative is the cleanup. Excess of this type of cement should be removed when the cement reaches a rubbery stage. If a practitioner misses this spot in the setting cycle, it is much harder to remove the excess.
Another comment I have heard from doctors using this type of cement relates to the long-term retention of restorations. Attendees at some of my lectures report that restorations they cement with polycarboxylate cements loosen and detach sooner than they would expect. While this can be a negative, if we think out of the box for a minute, this makes polycarboxylate a good choice for cementing long-term temporary restorations.
When we talk about glass ionomers, the big plus is fluoride release. In addition, this group of cements, such as Ketac-Cem, Fuji 1, and Shofu 1, exhibits true chemical bonding to tooth structure. Glass ionomers have low solubility, a coefficient of thermal expansion comparable to teeth, and are fairly easy to work with. The primary negative is that there can be postoperative sensitivity due to the low initial setting pH. An additional concern is the setting reaction’s sensitivity to moisture contamination. Care must be given to ensure that while this type of cement is setting, the cement margins of restorations are well protected from saliva.
The main advantages of resin cements are high compressive strength and low solubility. The earliest resin cements did not have the amount of filler particle that today’s cements do. As a result, there was significant color shift due to residual amine levels after the earlier resin cements set. Fortunately, polymer chemists improved these cements so that they are now a primary material in our armamentarium.
Current resin cements exhibit excellent esthetics, color stability, and can be divided into three categories based on the method of curing.
Resin cements polymerize by light curing, chemical curing, and dual curing. The last type indicates the cement can be light cured, and in areas where light cannot penetrate a restoration, the cement will chemically cure. This is sometimes referred to as a “dark cure.” As for those resin cements that started only with light curing, many now have catalysts that allow a doctor to convert the light-curing resin cement into a dual-cure version for certain situations.
A second way to categorize resin cements is based on the method used to prepare the tooth to which the cement is adhered. We have cements that are used with an etch and rinse, also known as total etch. Some examples are Insure, RelyX Veneer Cement, Nexus, and Calibra. There are cements used with a self-etch protocol for preparing the tooth surface. These include Panavia F 2.0 and new products Clearfil Esthetic Cement, and Bisco’s All-Bond SE. It should be noted that the lines are getting blurrier, and some dual-cure cements may be used with either etch and rinse or self-etch techniques.
A primary negative attached to the etch-and-rinse cements is the technique sensitivity. When using the etch-and-rinse technique, a practitioner must pay careful attention to many details — how long to etch, how much to rinse, and how moist or dry the tooth surface is.
When the self-etch technique is used with a resin cement, technique is important. But there is more leeway. Resin cements tend to cost a bit more. Sometimes there is postoperative sensitivity associated with resin cements, especially when they are used with the etch-and-rinse technique. The self-etch application has fewer sensitivity issues.
The newest resin cements are self-adhesive. I am particularly excited about these. Several years ago, I was a consultant to 3M ESPE. I suggested that dentists who would like to do more tooth-conservative restorations, such as onlays, use a resin cement to place them. But the existing bonding protocol for placing these restorations was complex and technique sensitive. I urged the company to develop a resin cement that could be used in a more conventional cementation technique, much like we do with other cements that do not require a bonding protocol.
While I did not create the first self-adhesive resin cement, it was my brainchild. After several years in development, the first cement in this group — RelyX Unicem, — was launched. Needless to say, it was a great feeling to see my idea become a real product. Today, use of this type of cement is increasing because of the high strength and low solubility advantages of resin cements, in general, and for the ease of use of this self-adhesive group. Cements in this group are G-Cem, RelyX Unicem, Maxcem, Monocem, Multilink Sprint, and Embrace. A helpful hint when using a cement in this group is to cure the marginal excess for about two seconds and remove the cured excess with a scaler. This will facilitate the final cleanup after the full set time elapses. Always be sure to read the instructions accompanying a product so as to ensure a complete set for the cement.
Your final group is the resin-modified glass ionomers. These cements include RelyX Luting Plus, Fuji Cem, and Fuji Plus. This group has resin filler particles mixed in with glass ionomers, which exhibit fluoride release comparable to the true glass ionomer cements. Resin-modified glass ionomers adhere to tooth structure and are less soluble than glass ionomers.
One major concern is the potential expansion after setting. This expansion most likely is due to water sorption. Since this type of cement expands, it can sometimes cause crack propagation in a nonmetallic restoration. A few years ago, there were reports of these cements causing marginal cracks in all-ceramic restorations. But today this problem seems to have been minimized.
Dr. Dalin: When we make decisions about purchasing cements, we are bombarded with different terms, physical properties, and more. Some examples of these terms are film thickness, working time, setting time, flexural and compressive strengths, water sorption, solubility, radiopacity, masking ability, and hydrophilic expansion. What should dentists look for when purchasing cements?
Dr. Fier: It can be overwhelming for a dentist to decide which cement to use. While I am not a dental materials expert, I will try to provide some helpful guidelines. I think water sorption and hydrophilic expansion should be as low as possible. A low film thickness helps to safeguard against a high occlusion after a restoration is cemented, and radiopacity is always desirable. Encapsulation or dispensing in a dual barrel syringe has made it easy to work with many of today’s cements. Additional things to look for are handling characteristics, and setting and working times. A practitioner must be comfortable with the amount of time he or she has in loading the cement into or onto the restorations once the mix is started.
With regard to masking ability, we are talking specifically about ceramic restorations. Whether veneers or crowns, it is important to remember that our restorations should be designed so that the restoration — not the cement — does most of the masking. Relying on a small film thickness of cement is not the way to block out undesirable undercolor. The key here is to provide the ceramist with the desired final shade and undershade of every tooth being restored every time. Cements can only provide a small amount of masking.
Some of the newer all-ceramic crowns with zirconia instead of metal copings have the inherent ability to mask out darker tooth colors. This makes it easy to use one’s cement of choice without concern for bleeding through of the undercolor. But once again, it is essential that the technician be given the prepared tooth shade (sometimes called the stump shade) so that the proper shade of zirconia may be selected.
Dr. Dalin: Do dentists need to stock every type of cement or should they narrow the list to just one or two?
Dr. Fier: With all the choices available, a dentist should decide what his or her primary cement will be. I think narrowing the choices to two or three is best. I always want to have a self-adhesive resin cement available. The others I consider essential are a resin-reinforced glass ionomer, which will provide the most fluoride protection, and a resin cement that has dual-cure capabilities. With these three types of cement, all types of restorations and techniques should be covered. As for brands, this is dependent on a doctor’s preference. Many manufacturers provide samples so one can try a particular cement before ordering in bulk.
Dr. Dalin: A critical factor in choosing the best cement is the type of restoration you are placing. Would you explain which cement you think works best with each of the following restorations: gold or metal inlay, onlay, or crown; porcelain-fused-to-gold or metal crown; all-ceramic inlay, onlay, or crown; porcelain veneer, bonded winged bridge (Maryland bridge); and zirconium crown?
Dr. Fier: Frankly, I don’t do all gold or metal inlays, onlays, or crowns. For my colleagues who do, they use a variety of cements for these restorations. Any of the cements that do not require light curing may be used for these all-metal restorations. With regard to PFM crowns, as mentioned earlier, most cements can be used as long as light curing is not essential for the cement to set. If a PFM crown has an all-porcelain margin, I prefer to use a resin-modified glass ionomer cement, an all-resin cement, or a self-adhesive resin cement. In this case, I silanate the porcelain margin so that the resin component of the cement can create a better marginal seal. As for all-ceramic or polymer glass inlays and onlays, I use a dual-cure resin cement. For all-ceramic crowns, I use self-adhesive resin cements more than ever.
Porcelain veneers are in their own category. Recently, I placed a case with a dual-cure resin cement because the veneers were thick in some areas. In this way, I was sure that if the curing light did not reach the deepest part of the veneer-tooth interface, the cement would still set. For most veneer cases, though, I still use a light cure-only resin cement. Maryland bridges may be cemented with self-etch resin cements. It is important to choose one that has the ability to block out the metal color. Generally, my choice for this type of restoration is Panavia F 2.0 in the opaque shade. Finally, we come to zirconia crowns. These restorations are strong enough to not require additional strength from bonding them to tooth structure. Therefore, they may be cemented with any cement that a practitioner prefers.
Dr. Dalin: How about temporary cements? I find myself frustrated by my choices for this type of cement. I can choose one that is retentive, but the patient might experience a fair amount of sensitivity. If I switch to one that has little or no sensitivity, a patient often returns due to lack of adhesion. What can you tell us about choices in the temporary cements category?
Dr. Fier: Jeff, temporary cementation can be challenging. The key is actually not in the cement but rather in the preparation design. The design should have some type of retention and resistance form. The other important element to consider in keeping temporaries attached is patient compliance. How many times do we tell patients not to chew gum, not to eat sticky foods, or to pull floss through the contact in a lateral direction so they don’t pull on the crown when removing the floss? In many cases when a restoration comes off, it’s because the patient abused the restoration. The current types of temporaray cements are zinc oxide eugenol based (ZOE), noneugenol-based, resin-based, or polycarboxylates.
While ZOE cements have a long track record and a sedative quality, it is advisable to avoid eugenol products if one is going to use a resin cement for placing the definitive restoration. The noneugenol products, such as Integrity TempGrip, Zone, TempBond NE, and TempoCem NE, have become very popular and manufacturers have recognized the growing need in this category. This noneugenol group now includes cements with desensitizing agents as well as antibacterial agents, such as GC Temp Advantage or Nex Temp. If a doctor needs greater retention for a temporary, a polycarboxylate cement may be used. This can either be a ready-made product, such as UltraTemp, or one could use a watered-down version of a standard “permanent” polycarboxylate cement, such as Durelon.
Dr. Dalin: We have choices when dealing with resin cements. Some dentists use total-etch adhesive systems while others use self-etching and priming systems. How much adhesion is needed? Are there ways to increase the amount of retention a cement will provide in those challenging situations dentists encounter?
Dr. Fier: The question as to how much adhesion is needed is excellent. While there have been many suggestions about what this value is, the answer, unfortunately, is not known. We could argue about bond strengths — whether shear, tensile, or microtensile — and be led to believe that the higher numbers give better adhesion. This is not necessarily the case. The different areas and surfaces of a tooth (dentin vs. enamel) may influence the amount of adhesion needed in a specific spot on a tooth. The nature of adhesion is more a function of the quality of the bond. So how much adhesion is really needed? The best answer is that you need as much as possible to retain the restoration depending on its inherent retention and resistance to dislodgement and the clinical situation in which the restoration is going. In my opinion, to try to quantify these variables is a futile exercise.
The thing we do know about resin cements is that the total-etch systems have the longest track record in this category. Therefore, in the long term, we might say they are the most durable. The self-etching and priming systems are probably next in the amount of time we have had them, while the self-adhesive cements have the shortest track records. Research shows the last category does not have as high bond strengths as the other two categories.
But the question that always needs to be asked about research is whether it is clinically relevant. In vitro studies do not always translate to real world dentistry. As for increasing retention when we face those challenging situations, my suggestion is to use a microetcher and sandblast the intaglio of the restoration to be cemented. Additionally, clean the surface of the tooth (or teeth) involved and use a total-etch resin cement. But if the tooth has a near exposure, it may be more prudent to use a self-etch and priming system or self-adhesive cement to protect against postop sensitivity.
Dr. Dalin: Dentists have had crowns come out with the core and post still inside. Is the weakest link in this situation the cementation of the post to the root?
Dr. Fier: I have also seen crowns come out with the post and core still inside them. Fortunately this happens rarely. One thing I learned in my early years of practice is that when I tried to use a low viscosity core material as a post cement (something I heard at a seminar), that technique often failed. I stopped doing this many years ago. Today I use a bonding system with resin cement to securely place posts rather than conventional cementation. I will etch the canal, rinse and dry it, apply a dual-cure adhesive — such as Clearfil PhotoBond — evaporate the excess solvent, and place the post with a layer of dual-cure resin cement, such as IntegraCem, on it.
Notice that I said evaporate the solvent. It is important to read the instructions accompanying any product. This often is not followed. By carefully following instructions, I have had great success in post retention. I cannot recall the last time a crown came out with the core and post still inside the crown. In the near future, I expect I will try cementing posts with a self-adhesive resin cement. But, so far, I have not done this.
Dr. Dalin: Is there anything else you want to discuss regarding dental cements?
Dr. Fier: As I mentioned earlier, I recommend following one important rule. No matter what the dental product, read the instructions before using the product. This gives you the best chance for success. With regard to dental cements, we have many choices. I am sure there are many more in the works.
Consider the goals you have when cementing a restoration. Do you want fluoride release? Do you care about hand mixing or do you want cement that comes in a cartridge mixing dispenser or in a capsule? Are you going to light cure or dual cure? These are some of the issues to consider. If you know what your goals are, you are on the way to making correct choices. Finally, keep in mind that all dental materials undergo deterioration. Cements are no different.
Remember where the cement restoration is going ... the mouth, which is a hostile environment at best. Also, remember the patient is responsible for caring for a restoration once it has been placed. The day of insertion is the best day in the life of a cement restoration. After that, it is out of your hands.
I hope this interview helps to demystify dental cements. Most importantly, while we learn from those cases that don’t work out well, we have so many more cases that are successful. As dentists, we have learned to be self-critical; we need that to become good at what we do. Let’s not forget to be proud of those cases that are successful. We have to remember not to be so hard on ourselves.
Marvin Fier, DDS, FASDA, ABAD, is a practicing clinician, a Fellow of the American College of Dentists, International College of Dentists, the American Society for Dental Aesthetics, a Diplomate of the American Board of Aesthetic Dentistry, a Fellow of the International Academy for Dental-Facial Esthetics, and a Fellow of the Academy of Dentistry International. Reach Dr. Fier via e-mail at [email protected].
Jeffrey B. Dalin, DDS, FACD, FAGD, FICD, practices general dentistry in St. Louis. He is the editor of St. Louis Dentistry magazine, and spokesman and critical-issue-response-team chairman for the Greater St. Louis Dental Society. He is a co-founder of the Give Kids A Smile program. Contact him at [email protected].
