Durable Adhesive Dentistry Is an Exact Science

Gary Alex, DMD (GA): Actually, adhesive dental procedures are widely used and routinely performed in restorative practices. Having said this, clinicians should be aware that it is one thing to place a bonded restoration and an entirely different thing to place one that will be durable over time. There are numerous factors that can be involved in why and where a bonded interface might fail. In the case of dentin, these include, but are not limited to, microleakage, nanoleakage, hydrolysis of the interface, incomplete penetration of primers/resins through acid-demineralized dentin, improper occlusion, operator error and/or poor clinical technique, poor product performance, inadequate polymerization, poor oral hygiene, and enzymatic breakdown of the adhesive interface. The late John Gwinnett, a highly respected academician, researcher, dentist, mentor, and teacher, taught his students to think of a bonded restoration as a chain-a series of links that, taken together, form a bonded assembly. And very much like a chain, our bonded restorations are only as strong and as durable as the weakest link.

ID: Why is bonding considered to be so technique-sensitive?

GA: The chemistries employed in adhesive systems can be sensitive to a multitude of factors, including the hydration state of the dentin and enamel prior to application (eg, dry, wet, moist), the application time, how the material is manipulated during application, and how long the adhesive is air-dried to evaporate the solvents after placement as well as factors related to light polymerization, such as light curing unit wavelength, intensity, collimation, technique, and duration. In addition, many adhesive systems are adversely affected when the working area is contaminated with blood or saliva. In short, durable adhesive dentistry is an exact science, and attention to the smallest details can be the difference between clinical success or failure.

ID: What considerations are most crucial when deciding which materials and protocols to utilize?

GA: There is no one-size-fits-all solution to any dental problem, and treatment decisions depend on numerous considerations. What is the specific clinical situation, and what are the potential solutions? What are the procedures and materials that the treating dentist is most comfortable using? What is the skill level of the treating dentist? How old is the patient? What can the patient afford? Should the restoration(s) be direct, indirect, or a combination of both? What is the occlusion like? Before deciding on a definitive treatment plan, dentists must evaluate many factors. But once the decision is made, they are obligated to be proficient at the plan's implementation. Dentists must also be flexible and able to "think on their feet" because the plan often has to be changed or modified as treatment progresses.

ID: What can dentists do to avoid potential pitfalls when bonding?

GA: We now have a number of excellent and chemically sound adhesive systems available. However, even good chemistry will not overcome poor clinical technique. If you want a better adhesive system, then become a better dentist. Meticulous attention to details such as control and isolation of the working area, proper conditioning and priming, proper solvent evaporation, and using a good curing light with a proper technique is critical if dentists want to avoid pitfalls and achieve success with adhesive dentistry.

ID: Bonding zirconia is somewhat of a polarizing topic. What are the arguments for each side?

GA: A misconception held by many dentists is that "you cannot bond to zirconia." The truth, however, is that you can bond very predictably and durably to zirconia surfaces using a combination of particle abrasion (ie, sandblasting), a phosphate ester primer (eg, 10-MDP), and an appropriate resin-based cement. Proper management of both the zirconia substrate and tooth tissues is crucial to achieving predictable and durable clinical outcomes. As a general rule, the intaglio surfaces of all zirconia restorations should be particle abraded and primed with a zirconia primer; however, this is not the case in every situation, and the use of a separate zirconia primer is contraindicated or not necessary with some materials. In this regard, manufacturers' instructions for use and other recommendations should be followed precisely for optimal results.

ID: What considerations are important when bonding multiple layers of materials?

GA: I assume that you are referring to bonding one layer of composite to another, which is often the case when placing direct composite restorations. First off, let me say that a composite restoration is very much like an iceberg. By that I mean that we can directly see and feel what's going on at the surface with our eyes and explorers, but what's really going on beneath that surface is something of a mystery. Layering a directly placed, light-polymerized composite is often necessary, even with bulk-fill composites, because the light energy is significantly attenuated as it traverses longer distances and into deep or thick layers (eg, the box of a deep class II). Insufficient energy may be delivered, resulting in decreased polymerization of the bonding agent and/or composite restorative. When dealing with deep preparations that are being restored with light-cure composites, a good rule of thumb is to increase curing times (assuming excessive heat generation is not an issue). Remember, there can be significant light attenuation even with high quality light-curing units.

ID: How about all-in-one adhesives? Are they "there" yet?

GA: Adhesive systems have progressed from the largely ineffective systems of the 1970s and early 1980s to the relatively successful total- and self-etching systems of today. The latest players in the adhesive marketplace are the so-called "universal adhesives." In order to develop a truly universal adhesive, very specific and synergistic functional and cross-linking monomers that are multifunctional in nature are required. They must be capable of reacting with a number of different substrates, be able to copolymerize with chemically compatible resin-based restoratives and cements, and have some hydrophilic character, yet at the same time, be as hydrophobic as possible once polymerized to discourage hydrolysis and water sorption over time. Although the current universal adhesives are not perfect, they offer a viable choice if they are correctly used. In theory, these systems have the potential to significantly simplify and expedite adhesive protocols and may indeed represent the next evolution in adhesive dentistry. I have written a detailed and comprehensive article on universal adhesives that I highly recommend to anyone seeking further information on this topic.¹

Gary Alex, DMD
Accredited Member
American Academy of Cosmetic Dentistry
Private Practice
Huntington, New York

1. Alex, G. Universal adhesives: the next evolution in adhesive dentistry? Compend Contin Educ Dent. 2015;36(1):15-26.