Simplifying Direct Composites With New Material Technology

Over the past 40 to 45 years, we have seen a dramatic progression in dental adhesives since Buonocore introduced the technique of etching enamel with phosphoric acid to improve the adhesion to enamel. In fact, the first dental adhesives bonded resins to enamel only, with little or no dentin adhesion. Subsequent generations of dental adhesives have dramatically improved the bond strength to dentin and the sealing of dentin margins while retaining a strong bond to enamel. Since patients are increasingly demanding more metal-free dentistry, the use of dental resins as cements or direct restorations will continue to rise.

This article discusses the progression of dental adhesives to the most recent generation of dental adhesives in which all the components are contained in the composite resin restoration.

A BRIEF HISTORY
There has been an evolution during the past 45 years in the development of dental bonding systems with variations in chemistry, application, mechanism, techniques, and effectiveness. Let us quickly review dental adhesives according to a series of generations allowing us to understand the general characteristics of each group.

The first- and second-generation bonding agents used during the 1960s and 1970s did not recommend etching the dentin, and relied on adhesion to the attached smear layer. The
weak bond strength (2 MPa to 6 MPa) to the smear layer still allowed dentin leakage with clinical margin stain.

The third-generation systems of the 1980s introduced acid etching of dentin and a separate primer designed to penetrate into the dentin tubules as a method to increase bond strength. These systems increased the bond strength to dentin (12 MPa to 15 MPa) and decreased dentin margin failure. However, with time, margin staining caused clinical failure.

The fourth-generation adhesive systems of the early 1990s used chemistry that penetrated both etched/decalcified dentin tubules and dentin substrate forming a “hybrid” layer of collagen and resin. Fusayama and Nakabayashi described the penetration of resin into dentin to give high bond strengths, as well as a dentin seal. In fact, Kanca introduced the idea of “wet bonding” with these systems. Some of the products in this category include: All-Bond 2 (Bisco), OptiBond FL (Kerr), Adper Scotchbond Multipurpose (3M ESPE). These bonding agent systems have the longest track record, as far as research goes, and clinically they have performed very well. In fact, OptiBond FL, an 18-year-old product, even received product of the year from REALITY magazine. The bond strengths for these fourth-generation adhesives were in the low-to-mid 20 MPa range, and significantly reduced margin leakage compared to earlier systems.2 These systems were technique sensitive requiring a very exacting and controlled application of an acid etching gel on enamel and dentin, followed by 2 or more components on both enamel and dentin. Because of the complexity presented with multiple bottles and steps, dentists began requesting a more simplified adhesive protocol.

The fifth-generation bonding systems introduced during the mid 1990s combined the primer and the adhesive in one bottle, while still maintaining high bond strengths. Some of the products in this category include: ExciTE (Ivoclar Vivadent), OptiBond Solo Plus (Kerr), Prime & Bond NT (DENTSPLY Caulk), Adper Singlebond (3M ESPE). Unit-dose packaging introduced during the fifth-generation bonding agents provides fresh chemistry for each procedure. However, controlled etching, surface wetness, and resin placement continued to be a clinical challenge for some clinicians.

The sixth-generation bonding systems introduced in the late 1990s and early 2000s also known as the “self-etching primers” was a dramatic leap forward in technology. The separate acid etching step was eliminated by incorporating an acidic primer that was placed on the enamel and dentin after tooth preparation. Several variations involved either mixing the acidic primer and adhesive before placement on the dentin and enamel, or leaving the primer on the tooth and then placing the adhesive over the primer. Some products in this class are Clearfil SF Bond (Kuraray), Simplicity (Apex), Adper Prompt, L-Pop (3M ESPE). These systems were also reported to reduce the incidence of post-treatment sensitivity found in previous systems. However, the bond strength to dentin and enamel was reported to be lower than the fourth- and fifth-generation systems.

The seventh-generation bonding systems are the “all-in-one” adhesives that combine etch, prime, and bond in a single solution. Seventh-generation bonding systems were introduced in late 2002. Laboratory studies show the bond strengths and margin sealing to be equal to the sixth-generation systems. Some of the products in this category include i-Bond (Heraeus Kulzer), Xeno (DENTSPLY Caulk), G-Bond (GC America), Complete (COSMEDENT), and OptiBond All-in-One (Kerr).

INTRODUCING SELF-ETCHING/SELF-BONDING RESTORATIVE COMPOSITES
A new category of composite resin restorative materials, which include what could be referred to as an “eighth-generation” bonding system, has just become available for use. This new technology features a bonding agent which is contained within the composite resin restorative material. A self-etching, self-adhering flowable composite technology eliminates the need for a separate bonding application step with composites for direct restorative procedures. Utilizing previous adhesive technology (found in the OptiBond system [Kerr]), this new self-etching, self-bonding flowable composite resin system (Vertise Flow [Kerr]), simplifies the placement of direct composite restorations.

Discussion
Vertise flowable composite has a relatively low modulus and acts as an elastic gradient between the dentin and the stiffer microhybrid, thus moderating polymerization shrinkage stress at the margins. Its low viscosity also wets the internal surfaces of the prepared cavity and helps ensure a well-adapted first layer, without the fear of over-etching. This self-etch, self-bonding flowable composite technology eliminates the need for a separate bonding application step usually required when placing direct composites. I have personally found that this product simplifies the direct restorative procedure by incorporating the bonding agent into the flowable material.

In the case described above, the material selected for the composite restoration was the enamel form of Herculite Ultra (Kerr). It is slightly more translucent than the dentin or opaque forms, allowing it to blend in with the rest of the tooth surface. Even with these latest generations of composite materials, there is significant stress that is placed on the tooth/resin interface due to shrinkage of the resin, so it was important to place the composite restoration with an incremental technique. It was essential to cure each layer completely for 20 seconds before placing the next level of composite.

CONCLUSION
Currently, clinicians have a variety of aesthetic and functional materials from which to choose. As dentists, we are always looking for something that is quick and simple to use, yet very effective. The new self-etching, self-adhering composite system, clinically demonstrated in this case report, offers some great benefits; whether it is used as your main adhesive flowable restorative choice or as an adjunctive bonding agent. It is the author’s opinion that these newest aesthetic composites will become a proven part of every restorative dentist’s protocol.