Dental Cementation Materials: Getting the Best Out of a Sticky Situation

Dental Cementation Materials: Getting the Best Out of a Sticky Situation. Photo courtesy of Viacheslav Lakobchuk / stock.adobe.com.

Dental cement is a workhorse material in many dental operatories. From cavity linings to fixing prosthodontic appliances to orthodontic applications, dental cements have many uses. As a result, there is no shortage of options to choose from. Here are a few things to know about dental cement when selecting the one that works best for you.

Each type of dental cement has its advantages and disadvantages. Nathaniel Lawson DMD, Ph.D., Associate Professor, Director, Division of Biomaterials UAB School of Dentistry divides cement into 2 categories: glass ionomer-based cement and adhesive resin cement.

Dr Lawson explains that glass ionomer, including resin-modified glass ionomer, (RMGI) cement is the most commonly used cement for zirconia and metal-based restorations. He says glass ionomers have the advantage of ease of use, moisture tolerance, and fluoride release. However, the disadvantage of glass ionomer types of cement is that they are not as retentive as adhesive resin cement. 

"They are composed of polyacrylic acid and fluoroaluminosilicate glass," Dr Lawson explains. "The polyacrylic acid allows a chemical bond between the glass ionomer and calcium in the tooth. The fluoroaluminosilicate glass allows fluoride release."

Adhesive resin cement is very similar to the resin composites used for direct restorations, per Dr Lawson. He says the difference is that most adhesive resin cements are less viscous than resin cements, and most are dual-cured. Adhesive resin cements are the most common cements for glass-based restorations, such as lithium disilicate or porcelain. The advantage of resin types of cement is they provide more retention and reinforce the crown material. In addition, adhesive resin types may be used with a separate tooth primer or without a tooth primer. The latter are known as self-adhesive resin cements, Dr Lawson explains. 

"Similar to resin composites, resin cements bond to the tooth through a hybrid layer," Dr Lawson says. "When used with a tooth primer, the tooth primer creates the hybrid layer. Self-adhesive cements can form a very thin hybrid layer due to the incorporation of acidic monomers in the cement."

Dental cement has a defined role in your restorations. For direct restorations, you can use it as a temporary or a cavity lining to protect the pulp. In indirect restorations, it is a luting agent that fills the space between your prep and the restoration.

The ideal properties of cement are also defined, which include:¹

• Strength
• Solubility
• Viscosity
• Biocompatibility
• Retention
• Esthetics
• Ease of manipulation

However, these properties differ greatly between cement. Per the Journal of Prosthetic Dentistry, the types of cement varied in elastic moduli and compressive proportional limit, resilience, strength, and toughness. They also varied in diametral tensile and flexural strength and toughness. Moreover, the researchers learned that storage time affected their flexibility differently, with the most significant increases in the glass ionomer types of cement over time.²

Making the Right Choice for Dental Cement Depends on Many Variables

It is incumbent on clinicians to determine which type of cement is best for each case. However, Jason Goodchild, DMD, Vice President of Clinical Affairs for Premier Dental Products Company, says some prep factors influence your cement choice based on the clinical situation. For example, your ability to isolate the area could drive your choice because you can't bond without isolation. In that situation, you would choose something more moisture tolerant, like a glass ionomer-based material.

"Bonding should be done in a well-controlled environment. You can't bond effectively when saliva and blood are present.In the cases where you cannot isolate effectively and you are doing the best you can, glass ionomer is more forgiving. Resin is not so forgiving in those environments," Dr Goodchild says.

The tooth's preparation is another factor in your decision. Dr Goodchild says a prep with at least 4 millimeters of occlusal-gingival height and between 10 and 20 degrees of taper gives you the freedom to choose almost any kind of cementation you want. When things aren't perfect in the prep, you have less options.

"If you have the right height and the right taper, you can use almost any type of cement. But if you don't have the enough height or the prep is over tapered, then the prep should be considered nonretentive. So, you might need the strength of a resin in a case like that because we know that resin is stronger than glass ionomer," Dr Goodchild says.

Moreover, there are a variety of different dental cements from which to choose. Dr Goodchild says the wide selection of cementation products can be confusing. For example, there are adhesive resins and self-adhesive resins, glass ionomers or RMGIs, and some cements have a light cure component while some do not, and some claim to be bioactive. All of these types of dental cement have features that provide advantages and present some disadvantages. Therefore, understanding the pros and cons of each and where they fit into the spectrum of cementation is essential.

"Also, you have to read the directions, just like any product in dentistry. All cements and bonding agents are not the same, so we need to understand the nuances. The folks that brought them to market, the manufacturers, and the chemists design them a certain way, and the directions reflect that. If we use them the right way, we should expect excellent results," Dr Goodchild says.

Most dentists want an easy, one-size-fits-all solution for cementation.Dr Goodchild says the self-adhesive resin cements sometimes called ‘universal’ want to be the Goldilocks approach to cementation.However, despite the name, universals don't work for every clinical situation, so Dr Goodchild uses a different approach, which he describes as an If-Then Equation. He sees it as a pragmatic approach to shifting variables, from prep conditions to substrate to restorative materials used.

"If I have this, then I should use that. So, if I have a nonretentive prep, I really should use something strong like resin. If I have a retentive prep, a perfect situation, then I'll use anything I want," Dr Goodchild explains, adding that the approach works with materials, too. "If I am using glass-ceramic, then resin cement. We know that. We also know that with thicker glass-ceramic restorations, you can sometimes get away with glass ionomer. If zirconia, then based on the height of the prep and the retentiveness, I choose glass-ionomer or resin."

When it comes to preparing the intaglio of the restoration, the substrate being used and the type of cement you choose may dictate how you prepare it, Dr Goodchild says. There are many types of substrates, including glass ceramics, zirconia or alumina, porelain-fused-to-metals (PFMs), Gold, and even resins. Clinicians need to know how to pre-treat them. For PFMs restorations in the past, Dr Goodchild said clinicians didn't have as much to do besides make sure it was clean. However, there are pretreatment issues to manage with ceramics, which Dr Goodchild says work with the If-Then approach. For example, if you have glass containing ceramic, then you etch it and silanate it. If you have zirconia, you sandblast or cleanse it, and then if resin is being used you should also prime it with an acidic phosphate monomer.

"There are a lot of great products out there for this. For example, we have one from Premier called the Universal Primer," Dr Goodchild says. "Other good examples are Z-Prime [BISCO] or Monobond Plus [Ivoclar Vivadent US]."

Another important consideration is the other products you might use in your workflow, like cleansers or desensitizers on the preparation before definite cementation.

Treatment planning with the end in mind can help you design a successful workflow with all of these components. Dr Goodchild says that it is essential to know the incompatibilities with your cement and eliminate any problems between these products.

"Because when you add in all these additional products—like the antibacterial scrub and then the desensitizing agent—well, then who knows how this is going to work?" Dr Goodchild says. "When we've got a great cementation plan upfront, we can follow that plan, and the restoration goes smoothly."

In addition, there is esthetics to consider. Dr Goodchild says that glass ionomer cement generally doesn't come in colors, and the esthetics are not as good as resins. On the other hand, resins come in a multitude of different shades to match restorations. So, for example, Dr Goodchild explains, if you are using a translucent material like a glass-ceramic veneer or a restoration in the anterior zone, you will choose resin.

"It's always a trade-off," Dr Goodchild says. "I always think of glass ionomers as easy to use and that they offer some moisture tolerability and fluoride release, at least initially. But they don't have as many shades and are not as strong as resin. Resin, on the other hand, is very strong. It's technique sensitive because you can't use it in a moist environment, so you need to isolate it. So, they are not as easy to use as glass ionomers. Understanding the strengths and weaknesses are of your materials helps you pick the right one."

References

1. Dental Cement. Pocket Dentistry. Accessed September 4, 2021. https://pocketdentistry.com/13-dental-cement/#s0070.

2. Li ZC, White SN. Mechanical properties of dental luting cements. J Prosthet Dent. 1999;81(5):597-609. doi:10.1016/s0022-3913(99)70216-7