Since they boast an unparalleled combination of esthetics and strength, glass ceramics have become one of today’s most popular options for veneers and all-ceramic crowns. They are rapidly taking over the restoration playing field, and with good reason.
But with the growing use of glass ceramics has come a barrage of new cement options and techniques. It has also introduced a new set of clinical challenges for clinicians looking to ensure successful cementation in restorations. Even seasoned professionals can find themselves scratching their head, unsure of what caused a glass-ceramic restoration to fail.
So, how can you ensure success when cementing glass ceramics? Here are four important tips to keep in mind.
1. Choose the right cement
The rise of glass ceramics has been accompanied by a new market flood of contemporary cements. With so many cements available, choosing the correct one from the wide range of material options can be challenging. However, selecting the appropriate cement can directly contribute to the bond’s longevity, as well as esthetics.
“The top three things any dentist should be looking for when cementing glass ceramics in an esthetic zone are the film thickness, the color of the dental adhesive and the durability of the bond over time,” says Sridhar Janyavula, BDS, MS, a clinical research dentist at Dentsply Sirona.
“Many bonding agents are thick and yellow, leading to pooling around the edges,” Janyavula continues. “This is particularly common with universal bonding agents that are ethanol based, as they present with a deep yellow color even after light curing. This can be avoided with an acetone solvent bonding agent.”
When cementing glass ceramics, Dr. Jeff Lineberry, a general dentist practicing in Mooresville, North Carolina,adds that it’s important to take into consideration what type of glass ceramic you are using. This is crucial because different types of restorations require different types of adhesives-and accordingly, different surface treatments of the tooth and/or restoration.
“What type of ceramic am I cementing-zirconia? Lithium disilicate?” he says. “Not knowing how to use a particular cement properly for a particular indication like this is a common mistake. You need to know the cement and the proper protocol.”
2. Know your materials
Once you choose your cement, you need to ensure you understand its capabilities-and the proper steps to employ it properly.
“It’s critical to know the restorative material choices that you make, as well as the material you use to bond or cement it into place,” says Dr. Lineberry. “I know my materials and the manufacturers’ recommendations and how it should be managed to get the best end result.”
“It’s also good to use well researched/documented material choices,” Dr. Lineberry adds. “This all adds to predictability. A smooth, no-sharp-angles proper preparation of the tooth for adequate thickness and proper isolation is always best for long-term success.”
Since preparation varies based on material type, knowing what is required for your selected material is paramount. All cements require some level of conditioning on the tooth substrate and glass ceramic, with the most common method being the application of hydrofluoric acid follows by silanization1-but the adhesion steps vary by cement, even within a particular class of cement.
For example, some resin cements need to be light cured, while others don’t. Some are self-etch or self-adhesive, and they vary in viscosity. As such, it’s important that clinicians are aware of the appropriate processes for material mixing, dispensing and application prior to cementation.
“This is why it’s important to know the precise instructions for use (IFUs) of the bonding material, and follow those IFUs,” emphasizes Dr. John Flucke, DPR’s technology editor who practices in Lee’s Summit, Missouri.
3. Take the extra step
It can be tempting to finish a restoration in as few steps as possible, but taking time to go the extra mile can have a big effect on restoration success.
“Glass ceramics and self-adhesive cements continue to gain popularity due to the relative ease of use overall,” Janyavula says. “I am a firm believer of Leonardo DaVinci’s less is more simplicity, but when it comes to bonding glass ceramics, taking an extra step can make a big difference.”
The extra step Janyavula refers to is applying a primer before the bonding agent. Using a pure silane primer helps increase the thickness of the bonding area, since most silanes have a water consistency that improves the bonding interface.
“As a safe practice, a clinician should apply a dedicated primer such as silane, for glass ceramics,” Janyavula adds. “If the bonding surface of the crown gets contaminated, you don’t need to re-etch the surface with hydrofluoric acid. You can just reapply the silane after drying the surface.”
In addition to this, Janyavula notes that, while the jury is still out, several research studies have found that using a silane primer can be more effective than simply using universal bonding agents.2 Simply put, self-adhesive cements may not provide the long-term bond strength that a successful restoration requires.
“Many dentists use a universal bonding agent or a self-adhesive cement, expecting the same desirable outcomes as full bonding protocol of adhesive cementation,” he explains. “However, such combinations to replace/eliminate adhesive and primer pairings continue to test low over applying a separate adhesive on the tooth and a silane primer on the intaglio surface of a crown.”
4. Utilize your curing light
Since contamination is such a big contributor to restoration failure, executing cementation effectively and quickly is important. A curing light can help with this process.
“One powerful secret is your curing light,” says Dr. Flucke. “When bonding restorations, almost all systems are dual cure. However, getting that initial jump start of the process by using the curing light helps seal the margins.
“This helps decrease the incidence of staining or caries at the margins-and also means the restoration is more stable because a large part of the bonded areas is already set,” he continues. “The restoration won’t shift on the tooth, allowing for contamination or other problems.”
This largely stems from the fact that most resin cements recommend a short light cycle of two to three seconds without waiting for two minutes of a self-curing cycle, which, while convenient and quick, can make a bond less reliable.
“This expedited curing can be a double-edged sword,” Janyavula agrees. “Potential micro-movements during active cleanup leads to permanent disruption of the gel phase without the bond integration.”
“The bottom line is that using a powerful curing light-that is frequently tested to ensure its quality-is important, not just to fixed prosthetics, but to every bonded procedure in the office,” Dr. Flucke states.
So, whether it’s selecting the right cement, or executing cementation effectively, every step is crucial in ensuring a restoration lasts.
“Remember that every step of the process is important,” Dr. Flucke concludes. “Bonding is the last thing that happens and it must be done right to ensure long-term clinical success.”
1. T. Tian, J. K.-H. Tsoi, J. P. Matinlinna, and M. F. Burrow, “Aspects of bonding between resin luting cements and glass ceramic materials,” Dental Materials, vol. 30, no. 7, pp. e147–e162, 2014.
2. Guimarães, Heloísa A B et al. “Simplified Surface Treatments for Ceramic Cementation: Use of Universal Adhesive and Self-Etching Ceramic Primer.” International journal of biomaterials vol. 2018 2598073. 31 Dec. 2018.