Laura Dorr is the former executive editor of DPR's Modern Dental Network and a regular contributing author.

Laura Dorr

	The history of dental adhesives quietly began with a scientist from Switzerland. In 1949, Oskar Hagger, a Swiss chemist for DeTrey/Amalgamated Dental Company, developed the first system of bonding acrylic resin to dentin. His Cavity Seal material, in conjunction with a chemical curing resin called Sevitron, debuted in 1951, and used dentin (rather than enamel) as the initial substrate for bonding.

	However, this discovery had little practical application until the mid-1950s, when the evolution of dental adhesives took off. These early first-generation discoveries paved the road for amazing advancements, from the no-etch and total etch systems of fourth and fifth generation dental adhesives, to the sixth, seventh and eighth generations of self-etch systems.

	But just how far have we come? Let’s explore the winding path to modern dental adhesives.

	In 1955, Michael Buonocore, DMD, MS, proposed the acid-etch technique for bonding. Having identified that a major problem of filling materials was a lack of adhesion to tooth structure, he set out how to increase bond strength

	“In our attempts to obtain bonding between filling materials and the tooth structure, several possibilities are being explored,” Dr. Buonocore wrote in his groundbreaking paper. “One of these is the alteration of the tooth surface by chemical treatment to produce a new surface to which present materials might adhere.”

	His research demonstrated that resin that contained glycerophosphoric acid dimethacrylate (NPG-GMA) could bond to acid-etched dentin, which improved adhesion to enamel.

	Despite the revolutionary development in esthetic dentistry, this first stab at bonding wasn’t very successful: Low bond strength (in the 1-3 MPa range) led to poor clinical results. Additionally, immersion in water and exposure to moisture would greater weaken the bond, making it largely impractical for use in the mouth. However, the stage was set for dental adhesive development.

	The second generation of bonding systems set out to improve upon the coupling agents that had been developed in the first generation. This generation added polymerizable phosphates to bis-GMA resins to promote bonding, creating an ionic bond to calcium in the tooth.

	Despite advancements in couple agents and a slightly increased bond strength of 4 to 6 MPa, the ionic bonds would still rapidly degrade when exposed to moisture, often resulting in debonding or microleakage.

	Additionally, the removal of the smear layer, which is a layer of organic and inorganic material on the tooth surface produced during cavity prep, was overlooked and led to unreliable bond strength. It wasn’t until later in the decade when David Eick, Phd, MS, identified the smear layer using an electron microprobe with a scanning electron microscope attachment that clinicians became aware of its existence and the effect it may be having on bond strength.

	Due to these challenges, this generation of bonding agents is no longer used, but it spurred the development of third-generation materials that focused on adjusting approaches to address the smear layer.

	After Dr. Eick’s discovery, removing or modifying the smear layer became a priority for the third generation of dental adhesives. These new bonding systems introduced the process of acid etching of the dentin, in an attempt to partially remove or disrupt the smear layer.

	The goal of acid etching was to open the dentin tubules so that smear layer particles could be more effectively removed. After the acid was rinsed off, a primer could be applied. Then, an unfilled resin was placed on both the enamel and dentin. While this method created a stronger bond of 12 to 15 MPa, it was a controversial approach, as many clinicians felt that dentin shouldn’t be etched.

	In the end, most unfilled resins failed to penetrate the smear layer efficiently, resulting in many of the same issues suffered by prior generations.

	The 1980s brought a breakthrough: The new fourth-generation materials could completely remove smear layers. Bond strengths skyrocketed to low- to mid-20s MPa, and had substantially less margin leakage than earlier systems.

	You had to work hard to achieve this success, however. Although they were effective when implemented correctly, the bonding systems were incredibly complex and required multiple steps. Clinicians needed to have perfect technique while performing controlled etching on enamel and dentin, and there was plenty of room for error throughout the numerous application steps and use of multiple bottles. 

	Despite the technique complications, fourth-generation materials are still considered the gold standard in bonding against which newer generations are judged. Boasting excellent clinical track records, fourth-generation systems, such as All-Bond 3 (BISCO), OptiBond Dual Cure (Kerr Dental) and ClearFil Liner Bond (Kuraray), featured unprecedented bond strength and reliability. This class of bonding agents also remains one of the most versatile, since they can be used for a variety of bonding protocols including self-, light- and dual-cure, as well as indirect and direct.

	With effective systems identified, the work is now in simplifying the process.

	Simplification was the name of the game for the fifth-generation total-etch bonding systems. Although the fourth-generation materials were effective, the process was lengthy and cumbersome, eating up valuable clinical time and leaving plenty of room for error. In addition, post-operative sensitivity had become an increasing issue with fourth-generation systems, as well as collagen collapse of demineralized dentin.

	Enter the one-bottle system. Products such as One-Step (BISCO), Admira Bond (VOCO) and OptiBond Solo Plus (Kerr Dental) combined adhesive and primer into one solution. These could be applied to the dentin and enamel at the same time with 35 to 37 percent phosphoric acid for just 15 to 20 seconds, eliminating the numerous applications and waiting periods of the previous generation.

	In addition to being much simpler than previous processes, the one-step system didn’t weaken bond strength; it was similar to the fourth-generation ratings of about 25 MPa. However, with the simplicity and bond strength of the new materials came some shortcomings that hadn’t been seen in the prior generation: The new adhesives were more susceptible to water degradation because the primer in the one-bottle systems were hydrophilic. (In fourth-generation systems, the primer was covered by a hydrophobic resin which protected it from moisture.

) Additionally, due to the nature of the one-bottle system, not all of the fifth-generation adhesives could be used with dual- or self-cured materials, making them less versatile.

	Drawbacks aside, the advent of one-bottle systems was well-accepted by the dental community, as it was also financially profitable for clinicians. Chair time was greatly reduced, meaning more patients could be seen, and only one product needed to be stocked, instead of numerous adhesives and primers. Successful bonding was getting easier by the day.

	Sixth generation (late 1990s-early 2000s)

	The advent of the self-etching primers occurred during the late 1990s, and was a game changer in dental adhesive technology. Sixth-generation systems were designed to eliminate the etching step, and require no etching on the dentin preparation surfaces. Instead, a pre-mixed etch-primer is applied to the tooth, followed by and adhesive application and light curing.

A timeline of dental adhesives. Image via the 

	Sixth-generation adhesive systems did return to a multiple-bottle system and require two products: an etch-primer and adhesive. However, for many clinicians the addition of a second bottle proved simpler because it eliminated the etching step required with fourth- and fifth-generation adhesives. Manufacturers aimed to make the mixing step easier by creating cartridges that combined the unmixed portions of the self-etch primer and adhesive in perfect ratio. For example, ACE All-Bond SE (BISCO), a sixth-generation type II adhesive, automatically combines the two materials when the clinician pushes on the cartridge dispenser, and also subsequently turns pink to show when the mixture is ready to use.

	Although sixth-generation adhesives have an impressive bond strength to dentin (41 MPa after 24 hours), the bond to enamel is up to 25 percent weaker than both of the two prior generations.

 Initial bond strength also diminishes drastically over time, which makes sixth-generation products less popular than other generations.

	One-bottle and self-etch systems were both incredibly significant developments, and the seventh generation took it further by combining the two. This great simplification included all the ingredients required for bonding - etch, primer and adhesive - in one bottle.

	The simplicity of it was unprecedented, and it was an exciting development when the products first became available on the market - the promise of consistent bond strength while eliminating mixing errors was understandably attractive. And the manufacturers delivered on these promises; there wasn’t any mixing required and bond strength was unwavering. Although the system streamlined procedures, it did present several challenges.

	One challenge was maintaining the stability of the solution. The ingredients in the adhesive systems are inherently acidic, and are prone to chemical breakdown and hydrolysis because they contain a large amount of water. This results in the adhesive system becoming unstable more quickly compared with past generations. Additionally, they are more hydrophilic than the two-step self-etch systems of the sixth generation and are more prone to moisture absorption.

	Another critical drawback was bond strength. Although the bond strength was consistent as promised, it was also incredibly low. Seventh-generation adhesives were found to have the lowest initial and long-term bond strength of any system on the market at the time. These issues led to mixed reviews from clinicians and a drop in popularity: In 2012, it was reported that as many fourth- and fifth-generation adhesives were sold as sixth and seventh generations.

	Eighth generation/Universal adhesives (2010)

	The bonding challenges presented in sixth- and seventh-generation materials became big considerations in the development of the eighth generation, or universal adhesives. These one-bottle systems pair etching, priming and bonding into one solution like previous generations, but with an added focus on bond strength.

	To increase bonding strength, researchers turned to the 10-MDP (methacryloyloxy-decyl-dihydrogen-phosphate) monomer. This monomer serves as the main adhesive in many of the universal bonding agents, as it is incredibly hydrophobic. Because a huge culprit in adhesive failure is water, a hydrophobic material is less susceptible to issues caused by moisture. This contrasts greatly with the hydrophilic seventh-generation adhesives.

	Additionally, 10-MDP has the added bonus of bonding well to a wide (or “universal”) range of materials, including composites, glass ceramics and zirconia, making it incredibly versatile and providing much broader applications than seventh-generation systems.

	For instance, products such as All-Bond Universal (BISCO) can be used as a primer and bond enhancer for the aforementioned, as well as with lithium disilicate, silica-based porcelain and alumina. In addition, universal adhesive systems such as All-Bond Universal can be used for both direct and indirect restorations, with either self-etch or total-etch protocols. It is also compatible with light-, self- or dual-cured composites.

	The incredible versatility of these universal adhesives has provided clinicians with convenient solutions that don’t compromise on strength and efficiency. They are timesavers that, regardless of clinical procedure, ensure that only one type of adhesive is necessary. In addition, a recent study found that eighth-generation bonding agents had higher tensile bond strength than both sixth and seventh generations (over 30 MPa).

	Whether you are a fan of the more traditional fourth- or fifth-generation systems, or prefer the convenience of a universal adhesive, the development of new dental-adhesive products continues at a fevered pace. The industry can expect to see increased options offering higher bond strength, greater simplicity and fewer restorative failures than ever before. Here’s to the next generation: We look forward to the advancements it will bring.

	1. Buonocore, MG. A simple method of increasing the adhesion of acrylic filling materials to enamel surfaces. 

	2. Sofan E, Sofan A, Palaia G, Tenore G, Romeo U, Migliau G. Classification review of dental adhesive systems: from the IV generation to the universal type. 

. 2017;8(1):1-17. doi:10.11138/ads/2017.8.1.001

	3. Eick JD, Wilko RA, Anderson CH, Sorensen SE. Scanning electron microscopy of cut tooth surfaces and identification of debris by use of the electron microprobe. 

. 1970;49(6):1359-1368. doi:10.1177/00220345700490063601

	4. Tao L, Pashley DH, Boyd L. Effect of different types of smear layers on dentin and enamel shear bond strengths.

.1988;4(4):208-216. doi:10.1016/s0109-5641(88)80066-6

	5. De Munck J, Van Landuyt K, Peumans M, et al. A critical review of the durability of adhesion to tooth tissue: methods and results. 

. 2005;842:118-132. doi:10.1177/154405910508400204

	6. Alex G. Is total-etch dead? Evidence suggests otherwise. 

	7. Kamble SS, Kandasamy B, Thillaigovindan R, Goyal NK, Talukdar P, Seal M. 

 comparative evaluation of tensile bond strength of 6(th), 7(th) and 8(th) generation dentin bonding agents. 

Articles

How the dental adhesives we know and love evolved from early discoveries that changed the way we practice restorative dentistry.

Stuck on you: The history of dental adhesives

	Everyone has their favorite cements for everyday use, but are those go-tos  the right choice for thin-walled restorations?

	Restorations with thinner walls, such as veneers, that provide natural-looking results require more finesse to ensure optimal esthetics. This might require you to look outside your usual arsenal or add a few extra steps to the procedure to guarantee high-quality outcomes. 

	“I take extra care with thin-walled restorations, and for veneers or thin crowns with limited retention, I use a cement system that has multiple steps: etching, and priming the tooth, cleaning and priming the crown, and finally cementing,” says Jennifer Sanders, DDM, a general dentist in private practice in Frenchtown, Montana. “Using a complete system ensures that the products behave well together.”

	Product advancement and ever-emerging technique developments have made the placement of veneers less complicated if you use the right materials. Selecting a cement with a viscosity level that will limit drifting after seating, is easy to dispense and apply (and remove for clean-up), and provides lasting color stability can greatly enhance the chance of success with veneers.

The adhesive armamentarium: Understanding the instruments, materials and supplies to keep on hand

	“I always do veneers with a low-viscosity material to ensure they seat easily,” says John Flucke, DDS, 

’s Chief Clinical Editor and Technology Editor, who practices in Lee’s Summit, Missouri. “I prefer to use materials that offer a variety of shades, are dual-cure, and are the ideal viscosity for my cases, such as PermaShade from Ultradent.” 

	Practitioners should look for light-cured total-etch, resin cements, such as Choice 2 (BISCO Dental), Prime&Bond elect (Dentsply Sirona) or RelyX Veneer Cement (3M), rather than self-adhesive versions. This is because self-adhesive resin cements are more prone to color change over time, ruining the appearance of the veneer. Also, light-cured resin cements don’t need to be mixed, allow for longer working time and shorter finishing time.

	“In general, I use a universal bonding agent after doing total etch, and use a light-cured resin for thin-walled restorations,” says Jeff Lineberry, DDS, a general dentist practicing in Mooresville, North Carolina. “In areas of thicker restorations or difficult access for proper curing, the use of other bonding adhesives that are compatible with dual-curing cements is essential.”

	Light-cured cements provide better color stability, and some, such as Choice 2, are available in a wide range of VITA and chromatic shades that mimic natural dentition.

	“This type of cements has thin film thickness, which allows for better dentinal sealing,” says Sridhar Janyavula, BDS, MS, a clinical research dentist at Dentsply Sirona. “Plus, you can visualize a glossy surface without the residual yellowing hue typical of most bonding agents.” 

	Essentially, the higher the translucency of the cement, the more natural the appearance.

 Opaque cements will hide the tooth’s natural luminescence and cause a more monochromatic effect that doesn’t look as natural or esthetic.

	Although some practitioners prefer dual-cure cements, and use them to great success, they may run into the aforementioned yellowing effect.

 This is due to the amine co-initiators and catalyst byproducts contained in dual-cure resin cements, which can sometimes cause veneer color change.

	Ensuring a cement is the proper temperature can also be critical for a successful restoration, so clinicians should avoid refrigerating resin veneer cements. Cements should be room temperature or warmer to avoid colder temperatures affecting the pseudoplastic behavior of the material, as well as flowability.

	“I think it’s a great idea to warm the material,” Dr. Flucke agrees. “This makes it flow even better.”

	Improving the flow properties can result in a more controlled seating with less drift, and makes cleanup a lot easier. Plus, warmer cement can help cut down on the likelihood of veneer fracture during placement.

	As with any restorative process, complete isolation needs to be achieved to prevent contamination. Once isolation is achieved, you can move on to the all-important step of color matching with a try-in paste.

	Many current adhesive systems include these water-soluble try-in pastes for shade testing, but it’s important to note that the try-in paste may not always match the end shade of the light-cured resin adhesive. One 2010 research study concluded that, “The color match achieved by the try-in paste has to be treated with caution and further assessment of the restoration made with the resin in place before curing is recommended.”

Because esthetics are key to veneer success, color matching should be approached with care.

	When it comes to actually seating the restoration, the risk of slippage or shifting is something to be taken seriously. This is where a low-viscosity cement becomes so critical, as it will prevent more shifting than a higher-viscosity alternative; plus, light-cured resin cements have a shorter finishing time, limiting the opportunities for slippage.

	In his practice, Dr. Flucke takes additional steps to ensure the veneer doesn’t shift. 

	“We also use a tacking tip on our curing light that sets a 2-to-3-mm area on the midfacial,” Dr. Flucke explains. “This holds the veneer in place while we clean the margins that are not yet set. Once all the excess material is removed from all the margins, we remove the tacking tip and bond the restoration into place.”

Read more about cementation best practices: Best practices for bonding with zirconia

	In addition to the consideration of viscosity, it’s important to select a cement that won’t require much pressure to seat.

	“Seating thin prosthetics, such as veneers, is ideally done with a material that requires less pressure to seat,” Dr. Flucke confirms. “That way, you do not have the risk of fracturing as you apply seating pressure.” 

	By choosing the correct cement and implementing it properly, dentists can create long-lasting, durable, thin-walled restorations that retain their color, while saving time, increasing profitability and pleasing patients. 

	“These concepts aren’t anything new,” Janyavula concludes. “We’ve been doing the same thing for decades. We just have improvised newer ways of doing it.” 

1. Kandil BSM, Hamdy AM, Aboelfadl AK, El-Anwar MI.

 Effect of ceramic translucency and luting cement shade on the color masking ability of laminate veneers. 

Dent Res J (Isfahan). 2019; 16(3):193-199.

	2. Munoz-Viveros C. How to choose a cement for porcelain laminate veneers

	3. Chadwick RG, McCabe JF, Carrick TE. Rheological properties of veneer trial pastes relevant to clinical success. 

. 2008;204(6)E11. doi: 10.1038/bdj.2008.136.

	4. ALGhazali N, Laukner J, Burnside G, Jarad FD, Smith PW, Preston AJ. An investigation into the effect of try-in pastes, uncured and cured resin cements on the overall color of ceramic veneer restorations: an in vitro study

2010;38(suppl 2):e78-e89. doi:10.1016/j.jdent.2010.08.013

Why identifying appropriate cement choices and proper handling are key to successful results with veneers and other esthetic restorations.

What to look for when cementing thin-walled restorations

	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.

	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.” 

	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 silanization

-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.

	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.

 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.”

	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,” 

	2.  Guimarães, Heloísa A B et al. “Simplified Surface Treatments for Ceramic Cementation: Use of Universal Adhesive and Self-Etching Ceramic Primer.” 

4 tips for better results when cementing glass ceramics

	Musicians have been singing for decades about how nothing lasts forever and, unfortunately, the lyric masters’ wisdom applies to more than just love or success. Dental restorations also fall prey to the old adage, despite our best attempts to prevent it. 

	Restoration failure is a big concern: Replacement of failed restorations makes up almost 70 percent of restorative dentistry cases.

 Overall, approximately 10 percent of restorations fail, according to a study published in the 

Journal of the American Dental Association

 that examined more than 1,700 cases over a seven-year time period.

The causes of these failures vary, and any number of factors could be at play in any given restoration failure. 

	And while some of these contributing issues are out of a clinician’s control, others, like adhesive failure, can be addressed, if a clinician takes the proper steps.

	“The old saying about ‘insanity is doing the same thing over and over while expecting different results’ is especially true when it comes to bonding,” says Dr. John Flucke, DPR’s technology editor who practices in Lee’s Summit, Missouri. “When something fails, that failure needs to be analyzed from multiple directions to find the solution.”

	Analyzing that process and taking the appropriate steps to remedying any underlying bonding or adhesive issues can greatly increase the chance of restoration success. But where should clinicians start?


	There are several steps clinicians can take to identify what caused the restoration failure. Dr. Flucke emphasizes figuring out where the bond failed should be the first place clinicians look.

	“First of all, it’s important to see where the cement 

,” he says. “If it’s bonded to the tooth and not the crown, you know it was a failure at the crown interface. If it is bonded to the crown and not the tooth, you know it was a problem at the tooth interface.”

	By identifying which bonding site suffered failure, the clinician can make further determinations about the cause of the failure.

	“Just identifying this piece of the puzzle can tell you a lot about the problem,” Dr. Flucke concludes.

	Dr. Jeff Lineberry, a general dentist practicing in Mooresville, North Carolina, agrees, and adds that it’s important to look at external factors that may have contributed to the failure. 

	“The most common thing to look for is where it failed,” he reiterates. “Did it fail at the tooth/cement interface, or the cement/restoration interface? But were there other factors, such as parafunctional habits?”


	Identifying the interface where bonding has failed can give clinicians critical clues as to what may have caused this failure. While issues with cement are common sources, it’s important to rule out other external factors that may have triggered the failure.

	For example, parafunctional habits, abnormal forces and tooth condition can all contribute to restoration failure, and are often common culprits.

	“In my practice, the main cause of restoration failure would be due to parafunctional habits,” Dr. Lineberry says. “Most failures have been due to patients clenching or grinding. I attempt to get patients engaged in managing the habits, but it is very patient-specific as to whether they follow through on managing it or not.”

	“It’s a process of elimination,” adds Dr. Jennifer Sanders, a general dentist in Frenchtown, Montana. “A restoration has come off-why? Look for decay or abnormal forces or any other external factors. If it’s not any of these, then you can assume it is likely adhesive failure.” 


	Isolation can be one of the trickiest steps in adhesive dentistry, but it’s also one of the most critical. Ensuring the field stays clean and dry can be the difference between adhesive success and failure, since the whole bonding process is predicated on a moisture-free process. If adhesion has failed in the past, there’s a good chance it can be attributed to isolation issues.

	“Improper isolation is a major contributor to restoration adhesive failure,” says Dr. Sanders. “It’s critical to use care to isolate.”

Getting the most out of your dental composites

	Since preventing contaminants, moisture and saliva from invading the field is the holy grail of successful bonding, Dr. Flucke recommends getting all hands on deck for adhesive procedures.

	“Isolation is absolutely critical,” he says. “Whether by cotton or devices such as Isolite or DryShield, it’s incredibly important. I recommend four-handed and sometimes even six-handed dentistry. Even in situations where EFDAs can cement crowns on their own, it is better to have four hands in the process just for the isolation alone.” 

	If the proper protocols are followed, but isolation is still very difficult, Dr. Sanders advocates switching to a cement that is more moisture tolerant to help prevent future failure. “If it just isn’t working, I will often go to a different cement.”


	So, how can clinicians avoid adhesive failure in new restorations as well as replacements? In addition to good isolation and proper bonding technique, staying up to date on proper protocols and complying with manufacturers’ instructions for use (IFUs) are important steps for ensuring adhesive success. 

	“Following IFUs is critical for long-term success,” Dr. Flucke explains. “All adhesives have their place, and when the IFUs are followed, most work very well.”

	Additionally, working with an adhesive system you know well, with steps you understand, can help avoid confusion during the bonding process. But it’s important to be flexible; if a bond just isn’t holding, you may need to adopt a different system or cement. Dr. Flucke suggests the following for evaluating if you need to make a change:

		If there is plenty of tooth structure and the cement has debonded from the prep, contamination in the bonding process may be in play, and the same system can be re-implemented, but with more care.

		If the bond has failed at the crown-resin interface or has debonded more than once, it may be time to consider implementing another system.

	In the end, it’s about evaluating which bonding techniques and strategies are working and which ones aren’t. 

	“Review your notes after a case and see what could have been missed or done better,” says Dr. Sanders. “Then take the appropriate steps to very carefully cement again.”

	So, while bonds may not last forever, taking these steps can ensure they succeed more regularly.

	“Take some time and revisit what happened and why,” Dr. Lineberry says. “Did you not have proper isolation? Or maybe you didn’t follow the manufacturer’s protocol or maybe it wasn’t as good as you thought it was. Whatever it was, taking time to identify where the issue arose can help you prevent it from happening again.”

 Adhesive/Dentin Interface: The Weak Link in the Composite Restoration. 

	2. Bernardo, Mario et al. Survival and reasons for failure of amalgam versus composite posterior restorations placed in a randomized clinical trial. 

The Journal of the American Dental Association

, Volume 138, Issue 6, 775 – 783 (2007).

Picking up the pieces when a dental restoration fails

While a dentist’s job has traditionally been to treat oral health, Dr. Todd Fincher believes dental practitioners should consider more than just a patient’s mouth-they should also be dedicated to improving sleep, and therefore a patient’s overall health.
	
	“It all depends on how you want to treat your patients,” he says. “Do you want to treat your patients just being a dentist that just handles their oral conditions or do you want to be known as their dental healthcare professional that looks at more than just their mouth, looks at their whole-body health and not just their oral health?”
	
	Practicing in Greenwood and Columbus, Miss., for more than 30 years, Dr. Fincher decided five years ago that he didn’t want to overlook whole-body health in his practices. He noticed there was a great need for extended care like this in his area, but no one in the region was providing it. So, he began offering sleep-apnea treatment and was shocked to discover that 60 to 70 percent of the patients he sees had some form of sleep apnea.
	
	“Nobody in our area was offering this. Overall it’s just a huge resource that needs to be brought to patients’ attention,” Dr. Fincher says.

	But adding these services to his practice took more than just a medical understanding of sleep apnea-he needed a way to integrate it into his practice workflow. After trying a few different software options, his team discovered Devdent.
	
	“We were really unsuccessful getting the results that we needed with the software we tried before Devdent,” Dr. Fincher explains. “But we found that Devdent made their Imagn Sleep Software very intuitive-and, out of all the software on the market, it’s the easiest and most user-friendly.
	
	“The Imagn Sleep software gives you great medical history and dental history, a good screening tool, and then ways to track your steps through the progression into the follow-up,” he adds. “It’s a really great all-in-one type program. It’s very comprehensive-almost too comprehensive. I really don’t think they can improve the software, to be honest. It exceeds all my needs. It’s powerful.”

	Before implementing Imagn Sleep in his practice though, he wanted to ensure he could use it effectively. He headed to Salt Lake City for intensive training on the Devdent software and sleep appliances.
	
	“Their training is so comprehensive,” he says. “I trained in-person, and then scheduled on-site training for my team. Our trainer was extremely competent, and she comes back on a yearly basis to check in on us and help us re-up. We’ve also used the remote training and it’s excellent.”

	In addition to the easy-to-use software, Dr. Fincher has been impressed by the effectiveness of Devdent’s home sleep-apnea testing and oral appliances, such as the Zmachine® Synergy sleep testing and the RiPPLE appliance system. And he can speak from experienceÂ­Â­Â­-a few years ago, he tested himself and was surprised to learn he had moderate sleep apnea.
	
	“I use the RiPPLE and after starting treatment with it for my own sleep apnea, I felt better and better every day,” he says. “We’re at our 100th sleep appliance with Devdent now, and we have only had one unsuccessful treatment. So, we are 99 percent successful with our Imagn appliances. That’s how good it is.  I know firsthand how effective it can be. And if it’s good enough for me, I guarantee it’s good enough for my patients.”
	
	Dr. Fincher is buoyed by his practice’s success with Devdent’s oral appliances and appreciates the benefits it brings to his patients in his community. And he credits much of it to the efficacy of Devdent’s complete system.
	
	“Devdent gives us exactly what we need in software, as well as the screening, sleep appliances and training that goes along with it,” he says. “For people that are looking to get into sleep-apnea treatment, this is a great system that you’re going to get great results from if you take your training seriously and do it like you are trained to do.”

	The Devdent Complete Sleep System is a six-step system that includes the Imagn Sleep Software, which can be implemented into the digital workflow. The home sleep testing machine, Zmachine Synergy, allows for scoring and interpreting of data by yourself or a team of board-certified sleep technicians. The RiPPLE oral appliance features a slim design to suit every patient. Imagn Medical Billing, education, and team training complete the system.

How Devdent’s complete sleep system is helping patients sleep easier and improving oral-systemic health. 

Start treating more than the mouth with Devdent's Sleep system

	Although zirconia has been around for decades, it is only recently that its popularity has skyrocketed. Zirconia is an incredibly strong material with a flexural strength five times greater than other ceramics. With recent advances in esthetics and CAD/CAM technology, zirconia is now being applied for a wide variety of clinical indications including single crowns, implants, endodontic posts, and both anterior and posterior dental restorations.

	“I think when dentists were introduced to zirconia, we saw it as a strong but ugly material,” Dr. Jason Goodchild, director of clinical affairs at Premier Dental, says. “Meaning, with the strength of the material came poor esthetics, and we could only use it for posterior teeth or where esthetics were not crucial. That has totally changed and now we can have both through the evolution of translucent or esthetic zirconia materials.”

At first, zirconia was only indicated for crowns, but that has changed over time, says Dr. Rolando Nuñez, manager of clinical research at BISCO.

	“In the beginning, zirconia was indicated for crowns-they were opaque and looked dull. Nowadays, there are multiple applications, anything from veneers to implants and denture structures. So, the future looks very promising.”

	However, as esthetics improve and applications for zirconia increase, new challenges arise for clinicians. To ensure bonding success with zirconia restorations, there are several important things for clinicians to keep in mind-because the esthetics, composition, or makeup of a restoration are irrelevant if it doesn’t stay bonded to the tooth. 

	Bonding with zirconia can be problematic; since the majority of bonding protocols are based on bonding to glass, which zirconia is not, different steps need to be followed.

	“Zirconia is a ceramic, but it is not an etchable ceramic, nor does it contain silica,” Dr. Nuñez explains. “It cannot be etched or silinated. So, the bonding procedure is different than the one used for feldspathic porcelain or lithium disilicate.”

	In fact, not recognizing the different needs of zirconia can be a critical mistake.

	“One of the most common errors when bonding a zirconia crown is when a clinician treats the zirconia like it is lithium disilicate,” Dr. Nathaniel Lawson, director of the division of biomaterials at the University of Alabama at Birmingham School of Dentistry, says. “Feldspathic porcelain and glass ceramics (like lithium disilicate) were glass containing.  Therefore, some glass was selectively removed by etching with hydrofluoric acid.  This created surface texture. Then a silane primer was used to chemically bond to the remaining glass. This won’t work with zirconia.

	One of the biggest errors a clinician can make when bonding to zirconia is not preparing-and decontaminating-the crown adequately.

	“One of the most important factors is how you prepare the intaglio (inside surface) of the zirconia crown before it is definitively cemented,” Dr. Goodchild says. “Not adequately preparing the intaglio of the crown before cementation is a critical mistake.”

	Dental zirconia (or zirconium oxide) bonds to phosphates. A core problem is that saliva contains a significant amount of phosphate.  This means that the presence of saliva contaminates the surface of zirconia restorations and hinders the development of a strong bond due to the depletion of bonding sites. Essentially, Dr. Lawson explains, “phosphate-based bonding sites can be blocked by phospholipids present in the saliva.”

Naturally, during try in, the zirconia will be exposed to saliva. So, before clinicians perform final bonding, it’s critical to decontaminate the zirconia intaglio.

	“Simply rinsing out the saliva does not remove phosphate groups that are bonded to the zirconia,” explains Dr. Sarah Jebreil, a cosmetic dentist practicing in Newport Beach, Calif. Instead, she recommends a cleaning product such as ZirClean™ (BISCO Dental Products) or Ivoclean (Ivoclar Vivadent) to decontaminate the surface-both of which can also be used on lithium disilicate and porcelain as well as zirconia.

	“Placing a product like these into the restoration allows the saliva phosphates that were bonded to the crown to become bonded to the zirconia oxide in the ZirClean or Ivoclean,” she explains.

	Dr. Lawson identifies saliva contamination and a lack of understanding of proper decontamination as critical factors that have hindered the success of zirconia restorations in the past.

	“Initially, clinicians attempted to use phosphoric acid to remove the salivary phospholipids,” he says. “The issue was that phosphoric acid would also bind to the phosphate-binding site on zirconia. Therefore, an alternate cleaning method should be used. Some options include cleaning solutions, re-sandblasting, or potentially sodium hypochlorite.”

	Sandblasting or light particle abrasion can be effective ways to enhance bonding by creating a fresh zirconia surface to bond to (Dr. Nuñez recommends sandblasting with 50-micron aluminum oxide powder at 40 psi for 20 seconds). It is important to remember however, that if the zirconia is not first decontaminated, the restoration is destined to fail. Several studies have found that this combination of chemical and mechanical pretreatment is necessary to ensure long-lasting, effective bonds

	In addition to decontamination and sandblasting, zirconia primers are an excellent tool for increasing bond strength. Since conventional silane coupling formulas cannot bind to metal-oxide ceramics, ceramic primers have unique adhesive monomers that allow them to bond to zirconia.

	“Bonding to zirconia relies on alumina sandblasting to create surface texture,” Dr. Lawson says. “It also requires the use of a different primer, 10-Methacryloxy dihydrogen phosphate (MDP), to chemically bond to zirconia. The MDP primer works through a phosphate-based bonding site on the zirconia.”

	Skipping the use of a primer can have negative repercussions for the restoration, and Drs. Nuñez, Jebreil, and Goodchild all emphasize the importance of zirconia primers.

	“A potential missed opportunity during the bonding process is not utilizing a zirconia primer,” Dr. Goodchild explains. “These primers contain an acidic phosphate monomer and act to enhance the bond.”

And primer options are plentiful. Some, like BISCO’s Z-PRIME™ Plus, are comprised exclusive of phosphate and carboxylic monomers and exclude silane completely, as it does not increase zirconia adhesion.

 Other primers include the monomers for both glass ceramic (silane) and zirconia (MDP), reducing the need to buy multiple types of primer. There are also cements (such as Unicem 2, from 3M ESPE) that contain the primers for ceramics, so no additional primer application is necessary. Thanks to the variety of primers on the market, clinicians should have no problem finding one that integrates easily into their workflow.

	Lastly, as with any restoration, the strength of the bond is critical to success. This means selecting the appropriate cement or bonding agent.

How to simplify the zirconia-bonding process for successful restorations.